1999 Periodic
Carbon Monoxide Emission Inventory

for the
Maricopa County, Arizona Nonattainment Area

November 2001
Revised August 2002

Prepared and submitted by:
Maricopa County Environmental Services Department
Air Quality Division
1001 North Central Avenue, Suite 695
Phoenix, Arizona 85004

1999 Periodic Carbon Monoxide Emission Inventory
for Maricopa County, Arizona
Errata
Nonroad Equipment Emissions (Chapter 4)
A recent review of the calculations used to develop 1999 emissions estimates for nonroad mobile
sources indicated that a number of correction factors were inadvertently applied when "growing"
the emissions estimates based on earlier 1996 calculations. In addition, a few minor errors were
found in the underlying 1996 data, which when corrected, also affected the 1999 emissions
values for 2- and 4-stroke gasoline equipment and diesel equipment. Corrections made to the
1999 calculations are described below. Revisions made to the 1996 data are more fully
described in the errata for the 1996 emissions inventory.
•

•

Two correction factors used to develop the 1996 nonroad emission inventory was incorrectly
re-applied when developing the 1999 emission inventory. This "NEVES A/B inventory
ratio" and a 50% increase in VOC emissions to account for running and resting losses from
lawn and garden equipment were removed from the revised 1999 calculations.
A 2.4% reduction in the projected growth rate of lawn and garden equipment had been
applied in 1996 to account for the Phoenix municipal xeriscape ordinance. Since no further
reductions are expected, this correction factor was removed from the 1999 calculations.

Taking the above changes into account, the following table summarizes the differences in 1999
annual and daily nonroad engine CO emissions.
Original Calculations
Revised Calculations
Difference

Annual CO (tpy)
148,013.5
175,893.8
+27,880.3

Daily CO (tpd)
350.66
406.46
+55.80

To ensure consistency among chapters, the above corrections have already been incorporated
into the August 2002 version of the inventory, and are reflected in the tables and graphics in the
Executive Summary and Chapters 1 and 4.

TABLE OF CONTENTS

LIST OF TABLES..................................................................................................................................................... iv
LIST OF FIGURES................................................................................................................................................... iv
EXECUTIVE SUMMARY .........................................................................................................................................1
SECTION 1. BACKGROUND AND EMISSIONS SUMMARY ...........................................................................3
1.1 Background....................................................................................................................................................3
1.1.1 Type of Inventory, Pollutants, and Source Categories.........................................................................3
1.1.2 Geographic Area ..................................................................................................................................3
1.1.3 Demographic Profile............................................................................................................................3
1.1.4 Agencies and Groups that Prepared and are Responsible for the Inventory ........................................5
1.2 Emissions Summary.......................................................................................................................................5
1.3 References for Section 1 ................................................................................................................................6
SECTION 2. INDIVIDUAL STATIONARY POINT SOURCES..........................................................................7
2.1 Introduction and Scope ..................................................................................................................................7
2.2 Compiling the Point Source List....................................................................................................................8
2.3 Procedures for Estimating CO Emissions from Point Sources ....................................................................13
2.3.1 Example 1: Natural Gas-Fired Power Plant .......................................................................................13
2.3.2 Example 2: Secondary Aluminum Smelting Furnace .......................................................................15
2.4 Emission Reduction Credits.........................................................................................................................15
2.5 References....................................................................................................................................................16
SECTION 3. AREA SOURCES ..............................................................................................................................17
3.1 Introduction and Scope ................................................................................................................................17
3.2 Methodology and Approach ........................................................................................................................17
3.3 Procedures for Estimating CO Emissions from Stationary Area Source Fuel Combustion.........................18
3.3.1 Industrial Area Source Fuel Combustion...........................................................................................19
3.3.1.1 Natural Gas External Combustion ........................................................................................19
3.3.1.2 Natural Gas Internal Combustion..........................................................................................19
3.3.1.3 Fuel Oil Internal and External Combustion ..........................................................................20
3.3.2 Commercial/Institutional Area Source Fuel Combustion ..................................................................21
3.3.2.1 Natural Gas External Fuel Combustion ................................................................................22
3.3.2.2 Natural Gas Internal Fuel Combustion .................................................................................22
3.3.3 Residential Area Source Fuel Combustion ........................................................................................24
3.4 Procedures for Estimating CO Emissions from Waste Disposal, Treatment and Recovery ........................25
3.4.1 On-Site Incineration...........................................................................................................................25
3.4.2 Open Burning.....................................................................................................................................26
3.4.2.1 Burning of Agricultural Ditch Banks and Fence Rows.........................................................27
3.4.2.2 Burning of Tumbleweeds......................................................................................................27
3.4.2.3 Burning of Trees ...................................................................................................................28
3.4.2.4 Burning for Land Clearance..................................................................................................29
3.4.2.5 Pest Prevention......................................................................................................................29
3.4.2.6 Summary of CO Emissions from Managed Burning ............................................................30
3.5 Procedures for Estimating CO Emissions from Miscellaneous Area Sources – Other Combustion ..........30
3.5.1 Calculation of Emissions from Forest Fires.......................................................................................30
3.5.2 Calculation of Emissions from Fireplaces and Wood Stoves ............................................................31
3.5.2.1 Proportion of Residential Units With Wood-Burning Devices.............................................31
3.5.2.2 Density and Types of Wood Burned in Maricopa County ....................................................32
3.5.2.3 Volume and Quantity of Wood Burned in Maricopa County ...............................................33
1999 CO Emissions Inventory

i

Maricopa County, AZ

3.5.2.4 Annual CO Emissions from Fireplaces, Woodstoves, and Firepits ......................................34
3.5.2.5 CO Season Daily Emissions from Fireplaces and Wood Stoves ..........................................34
3.5.3 Calculation of Emissions from Structure, Motor Vehicle, and Vegetation Fires...............................35
3.6 Summary of All Area Source Emissions ...................................................................................................36
3.7 References for Section 3 ..............................................................................................................................37
SECTION 4. NONROAD MOBILE SOURCES....................................................................................................38
4.1 Introduction and Scope ................................................................................................................................38
4.2 Procedure for Estimating Emissions from Aircraft......................................................................................38
4.2.1 Emission Factors................................................................................................................................38
4.2.2 Summary of Aircraft Emissions.........................................................................................................39
4.2.3 Examples............................................................................................................................................40
4.2.3.1 Phoenix Sky Harbor Air Carrier ...........................................................................................41
4.2.3.2 Phoenix Sky Harbor Air Taxi ...............................................................................................41
4.3 Procedure for Estimating Emissions from Locomotives..............................................................................42
4.3.1 Line Haul Locomotives (AMS 22-85-002-005) ................................................................................42
4.3.2 Yard Locomotives (AMS 22-85-002-010).........................................................................................43
4.3.3 Summary of Locomotive Emissions ..................................................................................................44
4.4 Gasoline and Diesel Nonroad Equipment ....................................................................................................44
4.5 Summary of All Nonroad Mobile Source Emissions...................................................................................46
4.6 References for Section 4 ..............................................................................................................................46
SECTION 5. ONROAD MOBILE SOURCES ......................................................................................................48
5.1 Introduction..................................................................................................................................................48
5.2 VMT Estimation Procedure .........................................................................................................................48
5.3 Speed Estimation Procedure ........................................................................................................................50
5.4 CO Season VMT Factor...............................................................................................................................51
5.5.1 Emission Factor Model ......................................................................................................................53
5.5.2 Development of Model Inputs ...........................................................................................................54
5.5.2.1 Control Section .....................................................................................................................54
5.5.2.2 I/M Descriptive Input Record ...............................................................................................55
5.5.2.3 Alternative I/M Credit Files..................................................................................................56
5.5.2.4 ATP Descriptive Input Record..............................................................................................57
5.5.2.5 Pressure Test Descriptive Input Record ................................................................................57
5.5.2.6 Scenario Records ..................................................................................................................58
5.5.2.7 Local Area Parameter Record ...............................................................................................58
5.5.2.8 Oxygenated Fuels Descriptive Record..................................................................................59
5.5.3 Model Outputs ...................................................................................................................................60
5.5.5 Summary of Emission Factors ...........................................................................................................60
5.5.6 Emission Estimates ............................................................................................................................60
5.6 Summary of CO Emissions from Onroad Mobile Sources ..........................................................................65
5.7 Quality Assurance Process...........................................................................................................................65
5.7.1 VMT Estimates ..................................................................................................................................65
5.7.2 Emission Factor Estimates .................................................................................................................65
5.7.3 Quality Review of 1999 Periodic CO Emission Inventory ................................................................65
5.8 References for Section 5 ..............................................................................................................................67
SECTION 6. QUALITY ASSURANCE .................................................................................................................68
6.1 Introduction..................................................................................................................................................68
6.2 Purpose of an Emissions Inventory..............................................................................................................68
6.3 Quality Assurance Staff ...............................................................................................................................69
6.4 Implementation ............................................................................................................................................69
6.5 Review and Evaluation of Inventory Elements............................................................................................69
6.5.1 General Statement..............................................................................................................................69
6.5.2 Point Sources .....................................................................................................................................70
6.5.3 Area Sources ......................................................................................................................................71
1999 CO Emissions Inventory

ii

Maricopa County, AZ

6.5.4 Nonroad Mobile Sources ...................................................................................................................72
6.5.5 Onroad Mobile Sources .....................................................................................................................72
6.6 Summary Statement .....................................................................................................................................72
6.7 References for Section 6 ..............................................................................................................................73

1999 CO Emissions Inventory

iii

Maricopa County, AZ

LIST OF TABLES
Table 1–1. 1999 Demographic Profile of the CO Nonattainment Area .......................................................................5
Table 1–2. Maricopa County 1999 Periodic CO Emissions Inventory Contacts .........................................................5
Table 1–3. 1999 Season Daily CO Emissions for the Maricopa County Nonattainment Area....................................6
Table 1–4. Annual 1999 CO Emissions for the Maricopa County Nonattainment Area .............................................6
Table 2–1. Individual Point Source Categories of Carbon Monoxide .........................................................................7
Table 2–2. 1999 Annual and Season Daily CO Emissions from All Point Sources ....................................................9
Table 2–3. Point Source CO Emissions, by Category................................................................................................10
Table 3–1. CO Area Source Categories .....................................................................................................................17
Table 3–2. 1999 CO Emissions from Industrial Area Sources ..................................................................................21
Table 3–3. Suppliers and Total Distribution of Natural Gas to Commercial/Institutional Sources ...........................22
Table 3–4. Summary of CO Emissions from Stationary Area Source Fuel Combustion...........................................24
Table 3–5. Selected Emission Factors and Fuel Loading Factors for Open Burning of Agricultural Materials ........26
Table 3–6. Burn Permit Data Used to Estimate Material Quantities Burned Within the Nonattainment Area..........27
Table 3–7. Summary of CO Emissions From Managed Burning ..............................................................................30
Table 3–8. Density of Wood Types Used in Wood-burning Devices in Maricopa County .......................................32
Table 3–9. Wood Mix and Composite Wood Density (CWD) for Wood Species Used for Firewood......................33
Table 3–10. Total CO Emissions from Structure, Automobile, and Vegetation Fires...............................................36
Table 3–11. Summary of All Area Source CO Emissions .........................................................................................36
Table 4–1. General Airports and Operation Data ......................................................................................................39
Table 4–2. Aircraft Emission Factors ........................................................................................................................39
Table 4–3. Annual and Season Daily 1999 Aviation Emissions................................................................................40
Table 4–4. Summary of Annual 1999 Emissions from Class I Line Haul Locomotives ...........................................43
Table 4–5. Summary of 1999 Annual and Season Daily CO Emissions from Locomotives .....................................44
Table 4–6. Summary of all Nonroad Equipment Emissions Within the Nonattainment Area...................................46
Table 4–7. Summary of all Nonroad Mobile Source Emissions ................................................................................46
Table 5–1. 1999 HPMS VMT by Area and Facility Type for the CO/Ozone Nonattainment Area ...........................50
Table 5–2. Average Daily Speeds For the 1999 Periodic Emissions Inventory (in mph)...........................................51
Table 5–3. Average Daily VMT During 1999 Carbon Monoxide Season (November 1999–January 2000) ...........52
Table 5–4. CO Emissions by Vehicle Class, Area Type, and Facility Type..............................................................61
Table 5–5. Daily Onroad Mobile Source CO Emissions (in kg/day) by Vehicle Class, Area Type
and Facility Type – Winter ......................................................................................................................66

LIST OF FIGURES
ES–1. Source Category Contributions to Season Day CO Emissions .........................................................................2
1–1. Maricopa County CO Nonattainment Area Boundaries....................................................................................4

1999 CO Emissions Inventory

iv

Maricopa County, AZ

EXECUTIVE SUMMARY
This carbon monoxide (CO) inventory was developed based on requirements in the Clean Air Act Amendments of 1990 (CAAA), passed by Congress and signed into law by the President in November 1990. Title I of the
CAAA contains provisions on the required development of carbon monoxide emission inventories for designated
areas that failed to meet the National Ambient Air Quality Standards (NAAQS) for carbon monoxide. Maricopa
County was designated a CO nonattainment area on November 15, 1990, and was reclassified as serious effective
August 28, 1996. Maricopa County Environmental Services Department (MCESD) prepared this 1999 periodic CO
emission inventory to meet the requirements of Title I of the CAAA.
This inventory provides calculations of both annual and average season day CO emissions for 1999. The
average season day CO emissions mainly cover the period from November 1998 through January 1999. The sources
of emissions are categorized in four areas: 1) point sources; 2) area sources; 3) nonroad mobile sources and 4)
onroad mobile sources.
A total of 41 individual point sources are identified in this CO inventory. These point sources include a)
those sources that emit 50 tons1 or more per year of CO, b) those sources that were listed as a point source in the
1990, 1993, 1996 CO emission inventories, c) those sources that were listed as point sources in the ozone
inventories, both past and present, and have CO emissions greater than 5 tons per year and d) those point sources
that are the only source of CO in a category that would otherwise have been considered an area source. Individual
stationary point sources account for 0.8 percent of the total average season day CO emissions or 9.09 tons.
Stationary point sources contributed an estimated 1753 tons of CO in 1999.
Area sources are those stationary sources in the nonattainment area that are too small to be considered point
sources but may be significant in numbers and emit significant amounts of CO. Stationary area sources account for
approximately 2.1 percent of the total average season day CO emissions or 24.06 tons per day. Stationary area
sources contributed 5,840 tons of CO in 1999.
Nonroad mobile sources include aircraft, locomotives, diesel equipment, 4-stroke gasoline equipment, and
2-stroke gasoline equipment in the nonattainment area. Nonroad mobile sources account for 50.0 percent of the total
average season day CO emissions or 573.95 tons daily. Nonroad mobile sources contributed 195,042 tons of CO in
1999.
The Maricopa Association of Governments (MAG) calculated onroad mobile source emissions. Emission
factors for seven vehicle type categories are calculated using MOBILE5a, the latest in a series of models approved
by the EPA for the purposes of estimating motor vehicle emission factors for planning. Onroad mobile sources

1

As the English system of measurement is used primarily in this document, the term "ton" refers to an English (or
short) ton, equal to 2,000 pounds.
1999 CO Emissions Inventory

1

Maricopa County, AZ

accounted for 47.1 percent of the total average season day CO emissions, or 540.41 tons per day. Onroad mobile
source annual emissions were not calculated. A chart of this information can be seen with Figure ES–1.
This report is structured to include an overview of the inventory process, tables of summary data, data
documentation, and quality assurance steps taken. Each section of the inventory is an independent discussion, which
includes an introduction, scope, method and approach for estimating emissions, subsections with example
calculations, and summary.

Figure ES-1. Source Category Contributions to Season Day CO Emissions
(Percentage of total season-day CO emissions)

Area Sources
(24.1
Areatons/day,
Sources
2.1%)

Point
Sources
Point
Sources
(9.1 tons/day,
1.1%
0.8%)

2.9%

Onroad
Mobile
Nonroad
Sources
Sources
(540.4 tons/day,
41.1%
47.1%)

Onroad

Nonroad Mobile
Mobile
Sources
Sources
(574 tons/day,
50.0%)
54.8%

1999 CO Emissions Inventory

2

Maricopa County, AZ

SECTION 1. BACKGROUND AND EMISSIONS SUMMARY
1.1

Background

1.1.1

Type of Inventory, Pollutants, and Source Categories
This carbon monoxide (CO) inventory was developed based on federal requirements stated in the Clean Air

Act Amendments of 1990 (CAAA), passed by Congress and signed into law by the President in November 1990.
Title I of the CAAA contains provisions on the required development of ozone and carbon monoxide emission
inventories for designated areas that failed to meet the National Ambient Air Quality Standards (NAAQS) for ozone
and carbon monoxide. The Maricopa County CO nonattainment area was classified as moderate with a design value
of 12.6 ppm, and has since been reclassified to serious. Consequently, Maricopa County Environmental Services
Department (MCESD) prepared this 1999 periodic CO emissions inventory.
This inventory quantifies both annual and average season day CO emissions from stationary point, area,
nonroad mobile, and onroad mobile emission sources for 1999. The season day CO emissions cover the period from
November 1998 through January 1999 (MCESD, 2001).
1.1.2

Geographic Area
The Maricopa County CO nonattainment area is approximately 1,962 square miles, or approximately 20

percent of the total Maricopa County land area. The geographic boundaries of the nonattainment area are shown in
Figure 1–1.
1.1.3

Demographic Profile
A demographic profile of the Maricopa County CO nonattainment area was provided by the Maricopa

Association of Governments (MAG) and is included as Appendix 1–1. This demographic profile was derived from
the MAG update of the population and socioeconomic database for Maricopa County (MAG, 2000).
The square miles within the nonattainment area boundary were calculated by digitizing the boundary and
summing the area within the boundary using ArcInfo GIS software. There are 1,962 square miles within the CO
nonattainment area boundary. Definitions of the terms and a breakdown of population, households, and
employment within the nonattainment area boundary are found in Table 1–1.

1999 CO Emissions Inventory

3

Maricopa County, AZ

Figure 1–1. Maricopa County CO Nonattainment Area Boundaries

1999 CO Emissions Inventory

4

Maricopa County, AZ

Table 1–1. 1999 Demographic Profile of the CO Nonattainment Area
Parameter
Total Population
Total Households
Total Employment:
– Industrial Employment
– Office Employment
– Retail Employment
– Public Employment
– Other Employment
•
•
•
•
•
•
•

1.1.4

Value
2,957,147
1,124,469
1,414,767
313,613
396,106
325,133
189,263
190,652

"Total population" is the sum of resident population in households, resident population in group
quarters, transient population, and seasonal population.
"Total households" is the sum of occupied resident, transient, and seasonal housing units.
"Industrial employment" includes those jobs in the manufacturing and wholesale trade categories.
"Office employment" includes finance, consulting, real estate, and insurance. The medical industry is
not included.
"Retail employment" is associated with the retail trade sector of the economy, e.g., department store,
grocery store, and restaurant workers.
"Public employment" includes police, military, museums, schools, government, and libraries.
"Other employment" is all employment not included in the above categories. Examples include
medical, postal, transportation, utilities, and communication.

Agencies and Groups that Prepared and are Responsible for the Inventory
The agency directly responsible for preparing and submitting the Maricopa County nonattainment area

1999 Periodic Carbon Monoxide Emissions Inventory is the Maricopa County Environmental Services Department
(MCESD). Carbon monoxide emissions inventories for nonattainment area stationary (point and area) sources and
nonroad mobile sources (aircraft and locomotive) were prepared by MCESD. The nonroad equipment source
emissions were determined by the EPA in 1990 and were adjusted by MCESD in 1996; the 1996 emissions were
then grown to estimate 1999 emissions. The Maricopa Association of Governments (MAG) prepared the onroad
mobile source CO emissions inventory. All preparation and quality control contacts are listed in Table 1–2.
Table 1–2. Maricopa County 1999 Periodic CO Emissions Inventory Contacts
Task / Section:
Emission Inventory Preparation:
Stationary Point, Area, and Nonroad Mobile Sources

Name and Affiliation

Transportation Data
Onroad Mobile Sources and Modeling
Modeling
Quality Assurance / Quality Control:
Stationary Point, Area, and Nonroad Mobile Sources
Transportation Data/Onroad Mobile Sources and Modeling
External QA
1.2

Phone

Renee Kongshaug, MCESD
Bob Downing, MCESD
Ruey-in Chiou, MAG
Roger Roy , MAG
Peter Hyde, ADEQ

(602) 506-4057
(602) 506-6790
(602) 254-6300
(602) 254-6300
(602) 207-7642

Jo Crumbaker, MCESD
Ruey-in Chiou, MAG
Randy Sedlacek, ADEQ

(602) 506-6705
(602) 254-6300
(602) 207-2300

Emissions Summary
Average season day CO emissions in the Maricopa County nonattainment area for 1999 are shown in Table

1–3, while annual CO emissions are listed in Table 1–4.
1999 CO Emissions Inventory

5

Maricopa County, AZ

Table 1–3. 1999 Season Daily CO Emissions for the Maricopa County Nonattainment Area
Tons CO/
Season Day
9.09
24.06
573.95
540.41
1,147.51

Source Type
Stationary Point Sources
Area Sources
Nonroad Mobile Sources
Onroad Mobile Sources
Total:

Table 1–4. Annual 1999 CO Emissions for the Maricopa County Nonattainment Area
Source Type
Stationary Point Sources
Area Sources
Nonroad Mobile Sources
Onroad Mobile Sources

Tons CO/Year
1,753
5,840
195,042
(not calculated)

The remainder of this report is organized as follows: Section 2 addresses the stationary point source
categories addressed in this inventory. A list of all point sources and their emissions with sample calculations and
summary tables can be seen in section 2. Sample point source reports and calculations can be found in Appendix 2.
Section 3 provides a complete explanation of each area source category. Methods of determining emissions and
references are also provided. Supporting documentation and calculations can be found in Appendix 3. Section 4
addresses the nonroad mobile sources inventory. Aircraft activity, locomotives, and nonroad equipment are
included in this section. Nonroad emissions information, growth factors, and nonroad equipment calculations are
shown in Appendix 4. Section 5 describes the estimation of the onroad mobile source inventory, while MOBILE5a
computer inputs and descriptions can be found in Appendix 5. Section 6 describes the quality assurance program
used to ensure that the inventory is accurate and complete. Copies of completed QA checklists documenting errors
found and how these errors were corrected are given in Appendix 6.
1.3

References for Section 1

Maricopa Association of Governments. 1999 Demographic Profile for Maricopa County Ozone and
Carbon Monoxide Non-Attainment Areas. July 2000.
Maricopa County Environmental Services Department. 1990 Base Year Carbon Monoxide Emission
Inventory. August 1993.
Maricopa County Environmental Services Department. 1993 Periodic Carbon Monoxide Emission
Inventory. September 1996.
Maricopa County Environmental Services Department. 1996 Periodic Carbon Monoxide Emission
Inventory. December 1998.
US Government Office of the Federal Register, National Archives and Records Administration. Code of
Federal Regulations. 40 CFR, Volume 56, 56694. Nov. 6, 1991.
US Government Office of the Federal Register, National Archives and Records Administration. Code of
Federal Regulations. 40 CFR, Volume 61, 39343. July 29, 1996.

1999 CO Emissions Inventory

6

Maricopa County, AZ

SECTION 2. INDIVIDUAL STATIONARY POINT SOURCES
2.1

Introduction and Scope
Maricopa County Environmental Services Department (MCESD) is the lead agency responsible for

compiling this 1999 periodic CO emissions point source inventory. MCESD is also responsible for identifying all
point sources within the nonattainment area, documenting the methods used to calculate emissions from each source,
and calculating and presenting the results. For the purposes of this inventory, a point source is defined as a
stationary operation that meets one or more of the following criteria:
•

It emitted 50 short tons or more of carbon monoxide (CO) in 1999; OR

•

It was included as a point source in the 1990, 1993 or 1996 CO periodic emission inventories; OR

•

It was included as a point source in the 1990, 1993, or 1996 ozone periodic emission inventories and
has measurable CO emissions; OR

•

It is the only CO source (or one of a few) in a category that would otherwise have been considered an
area source.

This section describes the point source data collection techniques and emission estimation methods, and
provides summary tables of annual and season-day point source CO emissions. Table 2–1 shows the point source
categories to be addressed in a CO emission inventory (U.S. EPA, 1991), along with those that are present in the
non-attainment area and thus included in this inventory.
Table 2–1. Individual Point Source Categories of Carbon Monoxide
External Fuel Combustion:
Utility Boilers
Industrial Boilers
Commercial/Institutional Boilers
Other External Fuel Combustion

Included
Included
Included
Included

Stationary Internal Combustion:
Gas Turbines
Reciprocating Engines
Cogeneration

Included
Included
Included

Waste Disposal:
Municipal Waste Combustion:
Refuse-Derived Fuel
Mass Burn
Coal-fired
Other

Included
Not included, not in area
Not included, not in area
Not included, not in area

1999 CO Emissions Inventory

7

Maricopa County, AZ

Table 2–1. Individual Point Source Categories of Carbon Monoxide (continued)
Industrial Processes:
Iron and Steel Manufacturing
Coke Production
Coke Pushing
Coke Oven Doors
Coke Byproduct Plant
Coke Charging, Coal Preheater
Topside Leaks, Quenching
Battery Stacks
Sintering
Electric Arc Furnaces
Other Process Units
Petroleum Refineries
Mineral Products
Cement
Glass
Other
Miscellaneous:
Aircraft/Rocket Engine Firing and Testing
2.2

Not included, not in area
Not included, not in area
Not included, not in area
Not included, not in area
Not included, not in area
Not included, not in area
Not included, not in area
Not included, not in area
Included
Included
Not included, not in area
Not included, not in area
Not included, not in area
Included
Included

Compiling the Point Source List
Applying the criteria for identifying point sources described above resulted in a preliminary list of 223

businesses. After a telephone conversation with Larry Biland of U.S. EPA Region IX, it was agreed to exclude
sources that (1) emitted less than 5 English tons of CO in 1999, and (2) were not included in prior years' CO
emissions inventories. These smaller sources are considered as part of the area source category. Applying this
additional criteria narrowed the point source list to 41 individual sources, listed in Table 2–2.
Detailed process-level emissions information for each point source is collected annually by the Maricopa
County Environmental Services Department. Each point source is identified by a Maricopa County business
identification (ID) number internal to the County's computerized permit database, as well as business name, and
physical address as specified in Table 2–2. (Firms whose names have changed since being reported in earlier
inventories are noted in the table.) All point source data will be forwarded to the U.S. Environmental Protection
Agency for use in the National Emission Inventory (NEI) database. For questions concerning the identification of
point sources and their emissions calculations, contact Bob Downing at bdowning@mail.maricopa.gov, or (602)
506-6883.
MCESD identified point sources within the nonattainment area through its Environmental Management
System (EMS) permit database. Activity levels were determined from annual emission reports, MCESD source
inspection reports, or telephone contacts with sources. Table 2–3 lists the point sources by the categories
(determined by process-level Source Classification Codes) within which CO emissions were reported.

1999 CO Emissions Inventory

8

Maricopa County, AZ

Table 2–2. 1999 Annual and Season Daily CO Emissions from All Point Sources
Business
ID No.
1075
3313
961
1074

SIC
4952
4911
7996
4952

29919
40233

4953
9511

26
1437

5082
3672

3536
355

2051
3724

354
31617
3966
3300
744
1254
1414
1415
881
1151
223
1878
52382
212

3341
3674
3674
9711
3325
8062
1442
1442
3674
3674
3524
8661
4911
3674

98
1014
238
1030
3315
4175
3316
3317
101
249

4911
3251
3272
2752
4911
4226
4911
4911
2011
3721

232
234
201
260
213
403
20706

7011
2023
1442
1442
1442
3354
3086

Business Name
91st Ave. Wastewater Treatment Plant
APS West Phoenix Power Plant
Big Surf
City of Phoenix 23rd Ave. Wastewater
Treatment Plant
City of Phoenix 27th Avenue Landfill
City of Scottsdale / Water Services
Division
Empire Machinery Co.
Hadco Phoenix Inc. / Sanmina Phoenix
Division
Holsum Bakery Inc.
Honeywell International Inc.
(formerly AlliedSignal Engines)
Imsamet of Arizona
Intel Corp. Chandler Campus (Fab 6)
Intel Corp. Ocotillo Campus (Fab 12)
Luke Air Force Base
M.E. West Castings Inc.
Maricopa Medical Center
Mesa Materials Inc. (Mesa)
Mesa Materials Inc. (Phoenix)
Motorola Inc.
Motorola Logic & Analog Tech Group
MTD Southwest Inc.
North Phoenix Baptist Church
Ocotillo Power Plant
ON Semiconductor
(formerly Motorola Inc.)
Palo Verde Nuclear Generating Station
Phoenix Brick Yard
Pre-Cast Manufacturing Co.
Quebecor World-Phoenix Division
Santan Generating Plant
SFPP LP
SRP Agua Fria
SRP Kyrene Steam Plant
Sunland Beef Co.
The Boeing Company (formerly
McDonnell Douglas Helicopter Systems)
The Phoenician Resort
United Dairymen of Arizona
United Metro Materials Inc. Plant #1
United Metro Materials Inc. Plant #11
United Metro Materials Inc. Plant #12
VAW of America Inc.
Wincup Holdings Inc.
TOTAL CO EMISSIONS:

Address
5615 S. 91st Ave.
4606 W. Hadley St.
1500 N. McClintock Dr.
2301 W. Durango St.

City
Tolleson
Phoenix
Tempe
Phoenix

ZIP
85353
85043
85281
85009

Annual
CO
(tons/yr)
25.28
101.01
1.06
27.48

Winter
Day CO
(lbs/day)
136.6
1,202.0 *
0.0
125.5

2800 S. 27th Ave.
16800 N. Hayden Rd.

Phoenix 85027
Scottsdale 85261

30.76
11.49

169.0
63.1

1725 S. Country Club Dr.
5020 S. 36th St.

Mesa
Phoenix

85210
85040

22.14
8.15

117.2
52.2

408 S. 23rd Ave.
111 S. 34th St.

Phoenix
Phoenix

85009
85034

7.25
31.36

55.8
172.3

3829 S. Estrella Pkwy.
5000 W. Chandler Blvd.
4500 S. Dobson Rd.
14002 W. Marauder St.
5857 S. Kyrene Rd.
2601 E. Roosevelt St.
3410 N. Higley Rd.
7845 W. Broadway Rd.
1300 N. Alma School Rd.
2200 W. Broadway Rd.
550 N. 54th St.
5757 N. Central Ave.
1500 E. University Dr.
5005 E. McDowell Rd.

Goodyear
Chandler
Chandler
Glendale
Tempe
Phoenix
Mesa
Phoenix
Chandler
Mesa
Chandler
Phoenix
Tempe
Phoenix

85338
85226
85248
85309
85283
85008
85205
85043
85224
85202
85226
85012
85281
85008

94.17
7.31
6.05
14.12
47.67
1.42
15.99
11.67
7.27
16.80
23.78
1.96
82.79
12.47

496.7
59.4
40.3
110.0
359.3
24.2
73.8
53.9
46.7
100.6
183.8
15.1
1,054.1 *
87.1

5801 S. Wintersburg Rd.
1814 S. 7th Ave.
301 W. Broadway Rd.
1850 E. Watkins St.
1005 S. Val Vista Dr.
49 N. 53rd Ave.
7302 W. Northern Ave.
7005 S. Kyrene Rd.
651 S. 91st Ave.
5000 E. McDowell Rd.

Tonopah
Phoenix
Phoenix
Phoenix
Gilbert
Phoenix
Glendale
Tempe
Tolleson
Phoenix

85354
85007
85041
85034
85296
85043
85303
85283
85353
85215

20.96
39.31
1.42
31.97
336.71
5.51
488.74
39.03
8.91
1.82

115.1
216.0
7.4
180.4
3,425.5 *
30.3
6,737.6 *
1,619.5 *
51.3
14.0

6000 E. Camelback Rd.
2036 S. Hardy Dr.
2875 S. 7th Ave.
3640 S. 19th Ave.
11920 W. Glendale Ave.
249 S. 51st Ave.
7980 W. Buckeye Rd.

Phoenix
Tempe
Phoenix
Phoenix
Glendale
Phoenix
Phoenix

85251
85282
85041
85009
85307
85043
85048

33.06
26.79
55.51
16.03
15.02
11.88
11.34
1,753.46

186.1
158.4
355.8
64.2
84.9
76.2
57.3
18,178.7

* Daily CO emissions from peaking power plants were calculated using data for a peak CO season day.

1999 CO Emissions Inventory

9

Maricopa County, AZ

The following is a list of sources that were included in the 1996 CO point source inventory, but that ceased
operations before or during 1999:
Business
ID No.
SIC Business Name
807
4911 Grove Cogeneration Plant
173
3325 Magotteaux-Chandler Inc.
808
4911 Scottsdale Princess Cogen Plant

Address
10853 N. Black Canyon Hwy.
24053 S. Arizona Ave.
7575 E. Princess Dr.

City
ZIP
Phoenix
85029
Chandler 85248
Scottsdale 85255

Pinal County, Arizona was contacted for information about major sources within 25 miles of the
metropolitan Phoenix non-attainment area boundaries. No sites in Pinal County met the criteria for inclusion as a
point source in this inventory. In addition, the Arizona Department of Environmental Quality was contacted to
identify any state-permitted source within the metropolitan Phoenix nonattainment area that should be included as a
point source; none were identified.
Table 2–3. Point Source CO Emissions, by Category
Business
Category
ID
SIC
EXTERNAL COMBUSTION:
Utility Boilers:
3313
4911
52382
4911
98
4911
3316
4911
3317
4911
Utility Boilers Total:
Industrial Boilers:
26
5082
1437
3672
3536
2051
355
3724
31617
3674
3966
3674
744
3325
1415
1442
1414
1442
881
3674
1151
3674
223
3524
212
3674
1014
3251
1030
2752
101
2011
249
3721
234
2023
201
1442
260
1442
213
1442
403
3354
20706
3086
Industrial Boilers Total:

1999 CO Emissions Inventory

Business Name

CO emissions
tons/yr
lbs/day

APS West Phoenix Power Plant
Ocotillo Power Plant
Palo Verde Nuclear Generating Station
SRP Agua Fria
SRP Kyrene Steam Plant

0.07
61.18
7.04
447.72
24.17
540.18

0.0
714.7
38.7
4,869.7
844.2
6,467.3

Empire Machinery Co.
Hadco Phoenix Inc. / Sanmina Phoenix
Holsum Bakery Inc.
Honeywell International Inc.
Intel Corp. Chandler Campus (Fab 6)
Intel Corp. Ocotillo Campus (Fab 12)
M.E. West Castings Inc.
Mesa Materials Inc. (Mesa)
Mesa Materials Inc. (Phoenix)
Motorola Inc.
Motorola Logic & Analog Technical Group
MTD Southwest Inc.
ON Semiconductor
Phoenix Brick Yard
Quebecor World-Phoenix Division
Sunland Beef Co.
The Boeing Company
United Dairymen of Arizona
United Metro Materials Inc. Plant #1
United Metro Materials Inc. Plant #11
United Metro Materials Inc. Plant #12
VAW of America Inc.
Wincup Holdings Inc.

1.45
8.15
7.25
5.97
6.82
6.05
5.31
1.34
1.97
7.06
16.55
0.08
11.90
0.05
31.97
8.91
1.56
26.79
0.43
0.99
0.90
9.08
11.34
171.91

5.1
52.2
55.8
32.8
44.4
40.3
34.3
6.2
9.1
38.8
90.9
1.4
65.4
0.3
180.4
51.4
12.0
158.4
2.8
6.3
5.3
58.2
57.3
1,009.1

10

Maricopa County, AZ

Table 2–3. Point Source Emissions by Category (continued)
Business
Category
ID
SIC
Business Name
EXTERNAL COMBUSTION:
Commercial/Institutional Boilers:
1075
4952 91st Ave. Wastewater Treatment Plant
1074
4952 City of Phoenix 23rd Ave. Wastewater
Treatment Plant
3300
9711 Luke Air Force Base
1254
8062 Maricopa Medical Center
1878
8661 North Phoenix Baptist Church
232
7011 The Phoenician Resort
Commercial/Institutional Boilers Total:
EXTERNAL COMBUSTION TOTAL:
INTERNAL COMBUSTION:
Turbines:
1075
4952
3313
4911
1074
4952
3300
52382
98
3315
3316
3317
Turbines Total:

9711
4911
4911
4911
4911
4911

91st Ave. Wastewater Treatment Plant
APS West Phoenix Power Plant
City of Phoenix 23rd Ave. Wastewater
Treatment Plant
Luke Air Force Base
Ocotillo Power Plant
Palo Verde Nuclear Generating Station
Santan Generating Plant
SRP Agua Fria
SRP Kyrene Steam Plant

Reciprocating Engines:
1075
4952
961
7996
1074
4952

91st Ave. Wastewater Treatment Plant
Big Surf
City of Phoenix 23rd Ave. Wastewater
Treatment Plant
40233
9511 City of Scottsdale / Water Services Div.
26
5082 Empire Machinery Co.
31617
3674 Intel Corp. Chandler Campus (Fab 6)
3300
9711 Luke Air Force Base
1254
8062 Maricopa Medical Center
881
3674 Motorola Inc.
1151
3674 Motorola Logic & Analog Technical Group
1878
8661 North Phoenix Baptist Church
212
3674 ON Semiconductor
98
4911 Palo Verde Nuclear Generating Station
238
3272 Pre-Cast Manufacturing Co.
Reciprocating Engines Total:
Cogeneration:
232
7011 The Phoenician Resort
Cogeneration Total:
INTERNAL COMBUSTION TOTAL:

1999 CO Emissions Inventory

11

CO emissions
tons/yr

CO emissions
lbs/day

3.64
0.12

33.1
1.3

5.06
0.96
0.06
4.06
13.89
725.98

44.5
5.3
0.5
26.8
111.5
7,587.9

0.01
100.93
15.39

0.1
1202.0
44.2

0.75
21.61
0.73
336.71
41.01
14.86
532.01

4.1
339.4
4.0
3,425.5
1,868.3
775.6
11,466.3

0.02
1.06
7.70

0.6
0.0
55.7

11.49
20.68
0.49
0.91
0.46
0.20
0.25
1.90
0.56
13.18
1.42
56.76

63.1
112.1
15.0
5.0
19.0
7.9
9.7
14.6
21.7
72.4
7.4
384.6

29.00
29.00
617.78

159.4
159.4
12,010.3

Maricopa County, AZ

Table 2–3. Point Source Emissions by Category (continued)
Business
Category
ID
SIC
WASTE DISPOSAL:
Refuse-Derived Fuel:
1075
4952
1074
4952

CO emissions
tons/yr

CO emissions
lbs/day

21.61
4.27

102.8
24.4

30.76
56.65

169.0
296.2

INDUSTRIAL PROCESSES:
Electric Arc Furnaces:
354
3341 Imsamet of Arizona
744
3325 M.E. West Castings Inc.
Electric Arc Furnaces Total:

94.17
9.00
103.17

496.7
69.1
565.8

Other Process Units:
744
3325 M.E. West Castings Inc.
4175
4226 SFPP LP
403
3354 VAW of America Inc.
Other Process Units Total:

33.36
5.51
2.80
41.67

256.0
30.3
18.0
304.3

10.33
14.02
39.26
0.26
55.08
15.04
14.12
148.11

47.7
64.7
215.7
2.0
353.1
57.9
79.7
820.8

292.95

1,690.8

25.39
7.41
23.70
56.50

139.5
56.4
182.3
378.2

29919
4953
WASTE DISPOSAL TOTAL:

Mineral Processes:
1415
1442
1414
1442
1014
3251
249
3721
201
1442
260
1442
213
1442
Mineral Processes Total:

Business Name
91st Ave. Wastewater Treatment Plant
City of Phoenix 23rd Ave. Wastewater
Treatment Plant
City of Phoenix 27th Avenue Landfill

Mesa Materials Inc. (Mesa)
Mesa Materials Inc. (Phoenix)
Phoenix Brick Yard
The Boeing Company
United Metro Materials Inc. Plant #1
United Metro Materials Inc. Plant #11
United Metro Materials Inc. Plant #12

INDUSTRIAL PROCESSES TOTAL:
MISCELLANEOUS PROCESSES:
Aircraft/Rocket Engine Firing and Testing:
355
3724 Honeywell International Inc.
3300
9711 Luke Air Force Base
223
3524 MTD Southwest Inc.
MISCELLANEOUS PROCESSES TOTAL:
TOTAL, ALL PROCESSES:2

2

1753.41

18,180.0

Totals are different from Table 2-2 due to rounding.

1999 CO Emissions Inventory

12

Maricopa County, AZ

2.3

Procedures for Estimating CO Emissions from Point Sources
Emission estimates for the point sources are determined from the annual emission inventory reports

submitted by the sources. EPA emission factor documents AP-42 (EPA, 1995 et seq.), AIRS 450/4-90-003 (EPA,
March 1990), and individual source tests are used to quantify emissions. Appendix 2–1 provides sample 1999
process-level emission inventory reports submitted by a source, while Appendix 2–2 includes a sample of emission
factors calculated using site-specific source test results.
Control efficiencies were determined by source tests when available and by AP-42 general factors
otherwise however no point sources had CO controls. The CO point sources in Maricopa County are not subject to
CO limitations, so no rule effectiveness factors were applied.
MCESD calculated the average season day CO emissions by adjusting the annual emissions to the
December, January, and February seasonal output percentages and then dividing them by the operating days per year
adjusted for the season. (The time frame is different than the normal winter season, because the emissions are
reported in quarters, starting with December 1998–February 1999.) The seasonal percentages and the operating
days per year were provided by each source. This calculation was done for all sources except the utilities. The
utilities are peaking power plants, which means the units operate on demand so the fuel combustion data for specific
days are the best representation of a daily emission estimate. The 1999 peak winter day was requested for worstcase scenario purposes. This data was provided by each facility and the calculation is illustrated in Example 1.
The annual and daily 1999 CO emissions estimates are presented in Table 2–3, which follows the two
examples. The two examples were provided to show the method used to calculate average season day CO
emissions. Example #1 illustrates the calculation of the actual season day CO emissions for a power plant. Example
#2 illustrates the calculation of average season day CO emissions for a non-combustion process from a metal
industry facility.
2.3.1

Example 1: Natural Gas-Fired Power Plant

SRP Agua Fria
7302 W. Northern Ave.
Phoenix, AZ
General Facility Information:
Salt River Project (SRP) operates a peaking electric generating plant with three gas/oil-fired boilers and
three turbines. The plant is brought on-line when extra generating capacity is needed during periods of peak
demand. To provide a reasonable calculation, SRP provided its operating schedule for a peak day in 1999 and 2000
for the CO season day during which the most electricity was generated. On this day, three boilers and three gas
turbines operated with an assumed 100% load. The AP-42 emission factors for gas-fired utility boilers are 84 lbs
CO/million cubic feet (MMCF) of gas, and 84 lbs CO/million cubic feet of gas for turbines. These factors are
1999 CO Emissions Inventory

13

Maricopa County, AZ

applied to the daily fuel consumption. AP-42 emission factors for diesel-fired equipment are also used to calculate
annual CO emissions. Totals for boilers and turbines are added to obtain the total SRP Agua Fria point source CO
emissions. SRP Agua Fria provided the following information:
1.

Peak Winter Day fuel consumption under 100% load (HFC):
Boilers:
57.97 MMCF
Gas Turbines:
22.24 MMCF

2.

Annual Fuel Consumption:
Boilers:
10,659.8 MMCF of natural gas + 4,970 gallons #2 diesel fuel oil
Turbines:
713.3 MMCF of natural gas + 260 gallons #2 diesel fuel oil
AP-42 Emission Factors:
Boilers, natural gas
Boilers, #2 fuel oil
Turbines, natural gas
Turbines, #2 fuel oil

(SCC 10100601)
(SCC 10100501)
(SCC 20100201)
(SCC 20100101)

= 84 lbs CO/MMCF
= 5 lbs CO/Mgal
= 84 lbs CO/MMCF
= 3.37 lbs CO/Mgal

Annual CO Emissions Calculation:
Natural Gas:
Boilers
= 10,659.8 MMCF × 84 lbs/MMCF
= 895,425 lbs/yr
Turbines
= 713.3 MMCF × 84 lbs/MMCF
= 59,917 lbs/yr
Total
= (895,425 + 59,917) = 955,342 lbs CO/yr
= 477.7 tons CO/yr
#2 Diesel:
Boilers

= 4.79 Mgal × 5 lbs/Mgal
= 24 lbs/yr
= 0.26 Mgal × 3.37 lbs/Mgal
= 0.9 lbs/yr
= (24 + 0.9) = 24.9 lbs CO/yr
= 0.01 tons CO/yr

Turbines
Total

Total Annual Emissions = Natural Gas + Diesel
= 955,342 lbs/yr + 24.9 lbs/yr
= 955,366.9 lbs/yr
= 477.7 tons CO/yr
CO Season Day Emissions Calculation:
Turbine Emissions = 22.24 MMCF × 84 lbs/MMCF
Turbine Emissions = 1,868 lbs/CO day
Boiler Emissions
Boiler Emissions

= 57.97 MMCF × 84 lbs/MMCF
= 4,869 lbs/CO day

Total CO Season Day Emissions = Total boilers + Total turbines
= 1,868 + 4,869
= 6,737 lb CO/day
= 3.37 tons CO/day

1999 CO Emissions Inventory

14

Maricopa County, AZ

2.3.2

Example 2: Secondary Aluminum Smelting Furnace

Imsamet of Arizona
3829 S. Estrella Pkwy.
Goodyear, AZ
General Facility Information:
This secondary foundry facility has two electric arc furnaces (EAFs) and two heat treat furnaces. Carbon
monoxide emissions of 21.5 lbs/hr of operation were calculated from stack tests conducted on the electric arc
furnaces in 1992. Production activity from this facility stayed essentially constant throughout the year; thus
emissions calculations are based on 8760 hours of operation annually.
Annual CO Emissions Calculation:
Source Emissions = Annual activity level × Emission factor = Total lbs CO/year
= 8760 hr/yr × 21.5 lbs CO/hr
= 188,340 lbs CO/yr
= 94.17 tons CO/yr
CO Season-day Emissions Calculation:
Source Emissions = Annual activity level × Emission factor
number of activity days
= 8760 hr/yr × 21.5 lbs CO/hr
365 days/yr
= 516 lbs CO/day
= 0.26 tons CO/day

2.4

Emission Reduction Credits
Two facilities that closed out their equipment during 1999 notified Maricopa County to request that their

emissions continue to be listed in the emission inventory for possible future use as emission reduction credits. The
emission reduction credits for carbon monoxide are as follows:
The Scottsdale Princess Cogeneration – 106 tons of pollutants
Anderson Clayton Oilseed Plant – 5.5 tons of pollutants
Therefore, the total emission reduction credits in 1999 are 111.5 tons.

1999 CO Emissions Inventory

15

Maricopa County, AZ

2.5

References

Maricopa County Environmental Services Department (MCESD), 1996. 1993 Base Year Carbon
Monoxide Emission Inventory. August 1996.
Maricopa County Environmental Services Department (MCESD), 1999. 1996 Periodic Carbon Monoxide
Emission Inventory. September 1999.
U.S. Environmental Protection Agency (US EPA), 1990. AIRS Facility Subsystem Source Classification
Codes and Emission Factor Listing for Criteria Air Pollutants. EPA-450/4-90-003. March 1990.
U. S. Environmental Protection Agency, 1991. Emission Inventory Requirements for Carbon Monoxide
State Implementation Plans. U.S. EPA/Office of Air Quality Planning and Standards, Rep. EPA 450/4-991-011,
March 1991.
U. S. Environmental Protection Agency, 1995. Compilation of Air Pollutant Emission Factors, Vol. I & II.
AP-42. 1995 et seq.

1999 CO Emissions Inventory

16

Maricopa County, AZ

SECTION 3. AREA SOURCES
3.1

Introduction and Scope
The EPA Emission Inventory Improvement Program produced a table (EPA, August 1999) of area source

categories which was evaluated for the CO periodic emissions inventory. Maricopa County regulations prohibit
residential incineration and open burning at industrial, commercial/institutional, and residential sources, therefore
these categories were excluded. Small-scale combustion sources identified in the EPA procedures document (EPA,
May 1991) are not addressed in the inventory because suitable emission factors are not available for estimation
purposes, activity data are very difficult and expensive to obtain, and the categories are determined to be negligible
contributors to emissions.
3.2

Methodology and Approach
Area source emissions are divided into three categories: fuel combustion, waste disposal, and

miscellaneous area sources. The Maricopa County Environmental Services Department (MCESD) prepared the area
source emission estimates for all area sources and provided quality assurance. Potential and included area sources
can be seen in Table 3–1. EPA emission factor documents are used to quantify emissions.
Table 3–1. CO Area Source Categories
Category / Subcategory
Stationary Source Fuel Combustion:
Utility
Industrial
Commercial/Institutional
Residential

all are point sources
included
included
included

Waste Disposal, Treatment and Recovery:
On-Site Incineration:
Industrial
Commercial/Institutional
Residential
Open Burning:
Industrial
Commercial/Institutional
Residential

included
included
included
not included, illegal
permitted only
not included, illegal
not included, illegal
not included, illegal

Miscellaneous Area Sources:
Other Combustion:
Forest Wildfires
Charcoal Grilling
Structure Fires
Fire Fighting Training
Fireplaces and Woodstoves
Aircraft/Rocket Engine
Firing and Testing

1999 CO Emissions Inventory

17

Comment

included
not quantified, optional
included
included
included
all are point sources

Maricopa County, AZ

One of five emission estimation approaches is used to calculate the area source emissions. Some area
source emissions were determined by summing the calculated emissions of individual contributing point sources.
Other source categories were calculated based on per capita, commodity consumption-related, or level-of-activity
approaches.
3.3

Procedures for Estimating CO Emissions from Stationary Area Source Fuel Combustion
The majority of fuel combustion in Maricopa County is natural gas. Small quantities of fuel oil, including

blends and waste are used by some industrial sources. The contribution of liquid petroleum gas (LPG) to total CO
emissions is considered insignificant in this area.
Maricopa County Environmental Services Department (MCESD) contacted four natural gas distribution
companies to collect natural gas distribution data. Three of the distribution companies are retail distribution
companies, while one is wholesale. A list of all four natural gas companies, contacts and distribution data can be
seen in Appendix 3–1. The data collected were used to estimate emissions by providing levels of natural gas used
by each stationary source in the nonattainment area.
Sales data from the wholesale distributor were obtained as a quality assurance check on the retail data. The
wholesale distributor reported supplying the three retail suppliers with approximately 39.2 billion cubic feet of
natural gas in 1999. This correlates with the total distribution to consumers reported by the three local retail
companies. The small difference found can be explained by two factors: 1) the identification of the nonattainment
area by the respective companies was approximate; and 2) other small, non-commercial sources of natural gas are
being utilized by the local natural gas retailers (e.g., the City of Mesa buys and sells digester gas from the City of
Phoenix 91st Avenue Wastewater Treatment Plant).
Each natural gas distribution company provided their seasonal distribution percentages based on the EPA
designated seasons of December–February, March–May, June–August, and September–November. The December–
February data are used to estimate total fuel consumption during the CO season and to calculate the emissions. It is
assumed that all natural gas sold is ultimately used in a combustion process, although each distribution company
does lose a minimal amount to leakage, damaged lines, and venting of lines during repairs.
MCESD requested distribution data showing the types of sources receiving the natural gas from the three
retail suppliers. This information allowed all sources to be categorized as either Industrial, Commercial/
Institutional, or Residential. The methods used to calculate the emissions from each source category were identical
to those used and presented in the 1990 Base Year CO Emissions Inventory (MCESD, 1993). The 1999 annual and
average season day CO emissions are presented in Table 3–4 following the example calculations.

1999 CO Emissions Inventory

18

Maricopa County, AZ

3.3.1

Industrial Area Source Fuel Combustion
3.3.1.1 Natural Gas External Combustion
Table 3–2 provides annual and season daily totals for the industrial fuel combustion category. Total natural

gas sales for the industrial user category is 10,016.1 million cubic feet (MMCF). This includes the transport
category provided by the retail distributors, which is the amount the distributors “transport” for those industrial
sources that buy gas directly from the natural gas wholesaler. From this amount, natural gas used by the point
sources listed in Section 1 (4,062.2 MMCF for external combustion and 158.5 MMCF used for internal combustion)
was subtracted out to avoid double counting. Therefore, a total of 5,795.4 MMCF was used by industrial area
sources.
It was assumed that natural gas for area sources is used for internal and external combustion in the same
ratio as for point sources. From the data above: (4,062.2 / [4,062.2 + 158.5] ) = 96%. Thus 96%, or 5,563.6
MMCF of natural gas was used in area source external combustion. MCESD chose the combustion rate category of
10–100 × 106 Btu/hr (SCC 10200602) to be representative of industrial area source natural gas external combustion.
The CO emission factor for this equipment is 84.0 lb/MMCF (EPA, July 1998). The 1999 CO emissions from
industrial area source natural gas external combustion are thus:
5,563.6 MMCF × 84 lb CO/MMCF = 467,341 lbs/yr = 233.7 tons/yr
3.3.1.2 Natural Gas Internal Combustion
For internal combustion area sources, it was estimated that:
5,795.4 MMCF for all area sources – 5,563.6 MMCF for area source external combustion = 231.8 MMCF
of natural gas was used. MCESD chose SCC 20200202 as representative of industrial area source internal
combustion, with CO emission factor of 399 lb/MMCF (EPA, July 1998). The 1999 CO emissions from industrial
area source natural gas internal combustion are thus:
231.8 MMCF × 399 lb CO/MMCF = 92,488 lbs/yr = 46.2 tons/yr
Therefore the total annual CO emissions from industrial area source natural gas combustion are as follows:
467,341 lbs + 92,488 lbs = 559,829 lbs or 279.9 tons/yr
The procedure for calculating 1999 season daily CO emissions for industrial external and internal
combustion is described below. To determine CO season emissions for industrial area sources, the total amount of
natural gas distributed in the December–February period was divided by the total amount of natural gas distributed
in 1999:

1999 CO Emissions Inventory

19

Maricopa County, AZ

2,604.2 MMCF × 100% = 26%
10,016.1 MMCF
According to Table 5.8–1 of the EPA procedures document (EPA, May 1991), fossil fuel use for industrial
area sources occurs throughout a six-day week. Season daily CO emissions are determined as follows:
Season Daily CO emissions
Annual Emissions (lb) × Seasonal Factor
(lb/day, external)
= Operation (days/week) × Season (weeks/yr)
= 467,342 lb × 0.26= 1,558 lb/day = 0.78 tons/day
6 × 13
Season Daily CO emissions
Annual Emissions (lb) × Seasonal Factor
(lb/day, internal)
= Operation (days/week) × Season (weeks/yr)
=

92,488 lb × 0.26= 308 lb/day = 0.15 tons/day
6 × 13

Therefore the total industrial area source natural gas season daily CO emissions are as follows:
1,558 lbs + 308 lbs = 1,866 lbs or 0.93 tons/day
3.3.1.3 Fuel Oil Internal and External Combustion
It was estimated that 5.45 million gallons of diesel and 2.46 million gallons of fuel oil were burned in
boilers, heaters, and engines in Maricopa County in 1999. These total amounts are based on a review of all 1999
emission inventories, with the assumption that an additional 5% was used by those sources that either:
•

were operating without a permit,

•

were permitted by the state but operating within the non-attainment area (certain portable sources), or

•

had a county permit, but were not surveyed in 1999 (some very small sources).
Area source fuel oil use was 164,770 gallons, primarily in boilers and heaters (external combustion); while

diesel use was 4,969,020 gallons primarily used in industrial and commercial engines (internal combustion). These
totals were calculated by subtracting fuel use reported by point sources listed in Section 1 from the total estimated
diesel and fuel oil usage. To calculate CO emissions, the total fuel used is multiplied by the relevant emission factor
for industrial equipment burning residual oil or diesel, obtained from AP-42 (EPA, 1998). For the external and
internal combustion CO emission factors, MCESD chose industrial external combustion boilers (SCC 10200501) at
5 lbs CO /1000 gallons and reciprocating international combustion engines (SCC 20200102) at 130 lbs CO/1000
gallons, respectively.
Fuel Oil External Combustion:
1999 Total CO Emissions = Total Fuel Used × CO Emission Factor
= 164,770 gallons × 5 lb/1000 gallons
= 824 lbs or 0.4 tons/yr

1999 CO Emissions Inventory

20

Maricopa County, AZ

Diesel Fuel Internal Combustion:
1999 Total CO Emissions = Total Fuel Used × CO Emission Factor
= 4,969,020 gallons × 130 lb/1000 gallons
= 645,973 lbs or 323.0 tons/yr
According to Table 5.8–1 of the EPA Procedures Document (EPA, May 1991), fossil fuel use for industrial
area sources is uniform throughout the year, six days per week. Average season daily CO emissions were
determined as follows:
Fuel Oil (External):
Season Daily
CO Emissions (lb/day)

Annual Emissions (lb)
= 6 days/week × 52 weeks/yr
= 824 / 312 = 2.64 lbs/day or 0.001 tons/day

Diesel (Internal):
Season Daily
CO Emissions (lb/day)

=

Annual Emissions (lb)
6 days/week × 52 weeks/yr

= 645,973 / 312 = 2070 lbs/day or 1.03 tons/day
Table 3–2 is a summary of the area source emissions in the industrial category.
Table 3–2. 1999 CO Emissions from Industrial Area Sources

Fuel Combustion Category
Natural Gas (External Combustion)
Natural Gas (Internal Combustion)
Fuel Oil (External and Internal Combustion)
Total:

3.3.2

1999 Annual
CO Emissions
(tons/yr)
233.7
46.2
323.4
603.3

1999 Season Day
CO Emissions
(tons/day)
0.78
0.15
1.03
1.96

Commercial/Institutional Area Source Fuel Combustion
This category of fuel consumption comprises natural gas burned in heating equipment, reciprocating

engines, and turbine engines. MCESD assumes that area source natural gas usage for boilers (and similar heating
equipment) and for engines is equivalent to the ratio of point source natural gas usage between boilers and engines.
The total natural gas usage reported as Commercial/Institutional is 14,202 million cubic feet. Point source fuel use
(243.93 MMCF for boilers and 163.19 MMCF for engines) was subtracted from this total to derive a value of 13,795
MMCF used by area sources. The ratio of internal to external combustion for area sources is assumed to be the
same as that for point sources (40.1% internal, 59.9% external combustion). Thus:
13,795 MMCF × 40.1% = 5,531.8 MMCF used for internal combustion
13,795 MMCF × 59.9% = 8,263.2 MMCF used in external combustion equipment

1999 CO Emissions Inventory

21

Maricopa County, AZ

3.3.2.1 Natural Gas External Fuel Combustion
A total of 8,263.2 MMCF was estimated to be used in external combustion area sources. This total is
multiplied by the CO emission factor of 84 lb/MMCF for SCC 201000201 (EPA, July 1998) to determine the annual
emissions.
1999 CO Emissions from Commercial/Institutional Heating = 8,263.2 MMCF × 84 lb/MMCF
= 694,109 lbs or 347.1 tons/yr
Calculation of the CO season daily emissions for commercial/institutional heating uses the DecemberFebruary natural gas distribution figures shown in Table 3-3.

Table 3–3. Suppliers and Total Distribution of Natural Gas to Commercial/Institutional Sources
(Area and Point Sources)

Supplier
Southwest Gas Corp. to "Commercial"
City of Mesa to "Commercial"
Black Mountain Gas Co. to "Commercial"
Total:

Million Cubic Feet (MMCF)
Annual
Dec.–Feb.
12,467.6
3,230.25
1,621.0
518.72
113.5
34.05
14,202.1
3,783.02

The total season consumption is divided by the annual consumption to determine the seasonal adjustment
factor for commercial/institutional external combustion as follows:
December-February cubic feet = 3,783.02 MMCF = 0.27
Total cubic feet
14,202.1 MMCF
According to Table 5.8–1 of the procedures document (EPA, May 1991), fossil fuel in the
commercial/institutional category was used throughout a six-day week. Therefore, the season daily CO emissions
from heating are calculated as follows:
Season Daily
=
Annual Emissions (lb)
CO Emissions (lb/day)
Operation (days/wk) × Season (weeks/yr)
= 694,109 lbs × 0.27
6 × 13
= 2,403 lbs/day or 1.20 tons/day

3.3.2.2 Natural Gas Internal Fuel Combustion
Area source commercial/institutional natural gas internal combustion was estimated to be 5,531.8 MMCF
in 1999 as explained above. It was assumed that natural gas for area sources is used for internal and external
combustion in the same ratio as for point sources. The total natural gas used by reciprocating engine point sources
1999 CO Emissions Inventory

22

Maricopa County, AZ

was 173.51 MMCF, or 54.4% of the total internal combustion engines. Thus, the area source usage of 5,531.8
MMCF was multiplied by 54.4% to get 3,009.3 MMCF of natural gas used by area source reciprocating engines.
This was multiplied by the CO emission factor to calculate annual emissions.
Reciprocating engine
emission factor used = 423 lb/MMCF* (EPA, July 2000)
*
Average of the four CO emission factors given for 2-stroke and 4-stroke lean burn engines,
SCC 20200252 and SCC 20200254.
Total 1999 CO emissions
from reciprocating engines = 3,009.3 MMCF × 423 lb/MMCF
= 1,272,934 lbs or 636.5 tons/yr
Seasonal operations in this category were distributed over a seven-day week and assumed to be constant
throughout the year. Therefore the average daily CO season emissions are calculated as follows:
Season Daily
= Annual Emissions (lb) × Seasonal Factor
CO Emissions (lb/day)
Operation (days/wk) × Season (weeks/yr)
= 1,272,934 lbs × 0.25
7 × 13
= 3,497 lbs/day or 1.75 tons/day
The natural gas used in reciprocating engines was subtracted from total natural gas usage for the category
to derive natural usage for turbine engines:
5,531.8 MMCF total – 3,009.3 MMCF in reciprocating engines = 2,522.5 MMCF burned in turbine engines
Turbine engine
emission factor

= 84 lb/MMCF (EPA, April 2000).

Total 1999 CO emissions
from turbine engines
= 2,522.5 MMCF × 84 lb/MMCF
= 211,890 lbs or 105.9 tons/yr
The seasonal adjustment factor for natural gas combustion in turbine engines is 25%, as determined above
for reciprocating engines. Seasonal operations in this category were distributed over a seven-day week. Therefore
the season daily CO emissions are calculated as follows:
Season Daily
= Annual Emissions (lb) × Seasonal Factor
CO Emissions (lb/day)
Operation (days/wk) × Season (weeks/yr)
= 211,890 lbs × 0.25
7 × 13
= 582.1 lbs/day or 0.30 tons/day
Internal combustion area source CO emissions (both natural gas reciprocating and turbine engines) are
shown below:
1999 CO Emissions Inventory

23

Maricopa County, AZ

Total 1999 CO Emissions = 636.5 + 105.9 = 742.4 tons/yr
Season Day CO Emissions = 1.75 + 0.30 = 2.05 tons/day
3.3.3

Residential Area Source Fuel Combustion
Other than wood, the only significant fuel for residential use in Maricopa County is natural gas. Natural

gas sales for the residential category of 14,475 million cubic feet (MMCF) were multiplied by an AP-42 CO
emission factor of 40 lb/MMCF to determine CO emissions for the year. MCESD applied the CO emission factor
for external combustion boilers (residential furnaces; EPA, July 1998). Total 1999 annual residential CO emissions
are calculated below:
1999 CO Emissions from
Residential Fuel Combustion = 14,475 MMCF × 40 lb/MMCF
= 579,000 lbs/yr or 289.5 tons/yr
The three natural gas companies provided natural gas distribution according to season. The total natural
gas distribution for residential use during the winter season (December to February) was 4,044 MMCF. The
seasonal adjustment factor was determined as follows:
December–February = 4,044 MMCF = 0.28
Annual Total
14,475 MMCF
According to Table 5.8–1 of the procedures document (EPA, May 1991), residential fuel combustion is equally
distributed throughout the week, so average daily CO-season emissions are determined as follows:
Season Daily
= Annual Emissions (lb) × Seasonal Factor
CO Emissions (lb/day)
Operation (days/wk) × Season (weeks/yr)
= 579,000 lbs × 0.28
7 × 13
= 1,778 lbs/day or 0.89 tons/day
Table 3–4. Summary of CO Emissions from Stationary Area Source Fuel Combustion
Stationary Area Source
Fuel Combustion Category
Industrial External Combustion
Industrial Internal Combustion
Commercial/Institutional External Combustion
Commercial/Institutional Internal Combustion
Residential External Combustion
Total:

1999 CO Emissions Inventory

24

1999 Emissions
(tons/yr)
234.7
366.4
347.1
742.4
289.5
1,980.1

CO Season Day
(tons/day)
0.78
1.17
1.20
2.05
0.89
6.09

Maricopa County, AZ

3.4

Procedures for Estimating CO Emissions from Waste Disposal, Treatment and Recovery
CO emissions from waste disposal, treatment, and recovery processes are grouped into two parts: (1)

emissions from on-site incineration sources; and (2) emissions from industrial, commercial/institutional, and
residential open burning. On-site incineration emissions are addressed below while open burning emissions are
included in Section 3.4.2.
3.4.1

On-Site Incineration
This category is separated into three classifications of on-site incineration: industrial, commercial/

institutional, and residential. Industrial incinerators are defined as incinerators used to burn materials from all
manufacturing establishments in SIC groups 20–39 and which are not classified as point sources. Industrial and
commercial/institutional incinerators are located at crematories and veterinarian facilities. Commercial/institutional
incinerators burn refuse and paper products from wholesale and retail trade establishments, service establishments,
and medical waste from hospitals and laboratories. Residential incinerators burn refuse and paper products from
homes and apartment complexes with less than 20 units.
All incinerators are required to be permitted by Maricopa County Environmental Services Department
(MCESD). A total of 29 commercial/institutional incinerators operated in Maricopa County during 1999. There
was no home or apartment complex in Maricopa County with less than 20 units that operated an incinerator.
The data used to calculate emissions from incinerators were obtained from 1999 emission reports which
were submitted to Maricopa County Environmental Services Department (Appendix 3–2). MCESD requires sources
to submit annual reports on emissions from processes and/or materials used at each source. For those sources
without 1999 emissions reported, the most recent reported data were used.
Annual carbon monoxide emissions for each source are determined by multiplying the total amount of
materials burned by the CO emission factor (EPA, October, 1996). Emission factors for incineration were obtained
from AP-42, Chapter 2: Solid Waste Disposal, 2.1 Refuse Combustion (EPA, Oct. 1996). Emissions were
determined by summing the total annual tons incinerated, and then using the following calculation:
Annual CO Emissions
from Onsite Incineration = Annual Tons Burned × Emission Factor
= 1,845 tons × 10 lbs/ton
= 18,450 lbs/yr or 9.23 tons/yr
Maricopa County Environmental Services Air Pollution Control Regulations Rule 313 does not require
controls for CO; so rule penetration and rule effectiveness are not reflected in the CO emission calculations.
Therefore, the total annual CO emissions from incinerators are 9.23 tons/year. Based on the average of the
operating schedules shown on each source's emissions report, the seasonal adjustment factor of 0.25 is used in the

1999 CO Emissions Inventory

25

Maricopa County, AZ

formula. An average operating schedule of 5 days a week is used. The calculation below illustrates 1999 CO
season daily emissions.
Season Daily
= Annual Emissions (lb) × Seasonal Factor
CO Emissions (lb/day)
Operation (days/wk) × Season (weeks/yr)
= 18,450 lbs × 0.25
5 × 13
= 71.0 lbs/day or 0.04 tons/day
3.4.2

Open Burning
This section includes emissions from controlled open burning which are regulated by the Maricopa County

Air Pollution Control Rules and Regulations. Permits are used to regulate the type of burning, manner, days and
times. MCESD issues permits primarily for purposes of agricultural ditch bank and fence row burning, tumbleweed
burning, land clearance, fire hazard/training, pest prevention, and trees (air curtain destructors). Amounts of
material burned in 1999 are estimated using the burn permits issued. To determine total CO emissions in this
category, calculations are made for each type of burning and then added together. Fire training is included in the
following section with structure fires.
CO emission factors are given in pounds of CO per ton of vegetation burned. The EPA fuel loading factors
provide an estimate of tons of specific vegetation produced per acre (amount produced is considered the amount
burned). Emission factors and fuel loading factors were obtained from AP-42 Table 2.5–5 (EPA, Jan. 1995). An
excerpt of the factors used is reprinted in Table 3–5.
Table 3–5. Selected Emission Factors and Fuel Loading Factors for Open Burning of Agricultural Materials
CO Emission Factor
Fuel Loading Factor
Refuse Category
(lb CO/ton)
(waste production, ton/acre)
Weeds: Unspecified
85
3.2
Tumbleweeds
309
0.1
Orchard Crops: Citrus *
81
1.0
Orchard Crops: Unspecified
52
1.6
Field Crops: Unspecified
117
2.0
*
The weight of citrus trees (the fuel-loading factor) is estimated to be 500 lbs/tree (MCESD, Aug. 1993).
A summary of the burn permit data is shown in Table 3–6. The calculation of emissions from the burning
of ditch banks and fence rows is included for illustration.

1999 CO Emissions Inventory

26

Maricopa County, AZ

Table 3–6. Burn Permit Data Used to Estimate Material Quantities Burned Within the Nonattainment Area
Type of Burning
Ditch Banks and Fence Rows
Tumbleweeds
Air Curtain Destructors
Land Clearance
Pest Prevention

Amount of Burning
Annual (1999)
CO Season
5,935,448 ft
(not allowed)
2,155 piles
32 piles
4,044 trees
1,040 trees
6397.16 acres
66.12 acres
59 piles
24 piles
55 acres
55 acres

3.4.2.1 Burning of Agricultural Ditch Banks and Fence Rows
According to air quality investigators at MCESD, ditch bank and fence row widths are five to ten feet and
four feet respectively. These permits are issued for one year and burning occurs at least twice a year. Since there is
no data kept regarding actual width, an average of seven feet was assumed for an equal prevalence of ditch banks
and fence rows. It was assumed that the total permitted length was within the nonattainment area, or within 25
miles, so the entire length was used in the calculation.
To calculate the amount of material burned on ditch banks and fence rows, MCESD estimated the area
burned and multiplied that by the fuel loading factor (see Table 3–6 above) which relates acres to tons of material.
The acres of ditch banks and fence rows burned are estimated as follows:
Lengths specified in permits total

= 5,935,448 ft

Acres specified

= (5,935,448 ft length × 7 ft width × 2 burns/yr × (1acre / 43,560 ft2)
= 83,096,272 / 43,560
= 1,907.63 acres

The following formula is used to convert the acres of ditch banks and fence rows burned to tons of
unspecified weeds burned:
Total tons burned = 1,907.63 acres × 3.2 tons/acre = 6,104.4 tons/yr
Total 1999 CO from Ditch Bank and Fence Row burning = 6,104.4 tons × 85 lb CO/ton
= 518,874 lb CO = 259.44 tons CO/yr
Since ditch bank and fence row burning is not allowed from November to February each year, the daily
emissions during the CO season are zero.
3.4.2.2 Burning of Tumbleweeds
Permittees are required to pile tumbleweeds before burning. Tumbleweed burn permittees specify the
amount burned in piles. A pile of tumbleweeds fifteen feet in diameter and five feet high was estimated by the
Maricopa County/University of Arizona Cooperative Extension Service to weigh 200 lb (MCESD, 1993). This is
the same as the AP-42 fuel-loading factor for 1 acre.

1999 CO Emissions Inventory

27

Maricopa County, AZ

In 1999, it was estimated that 2,155 piles or acres of tumbleweeds were burned in the Maricopa County
nonattainment area from burn permit data. Using the AP-42 fuel-loading factor of 0.1 ton/acre for Russian thistle
(tumbleweed), the total weight burned is calculated as follows:
2,155 acres × 0.1 tons/acres = 215.5 tons
Emissions are calculated according to the following formula:
= tons burned × emission factor

Annual Tumbleweed emissions

Total 1999 CO emissions from tumbleweed = 215.5 tons/yr × 309 lb CO/ton burned
= 66,590 lbs/yr or 33.3 tons/yr
Tumbleweed burn permits are valid for one month. Daily season emissions were determined using the
permits issued between December and February. Of the 2,155 acres for which permits were issued in 1999, 32 acres
were permitted in the winter. Burning was considered to have occurred evenly during the two issuance months. In
the same manner as above, the total weight burned is estimated at (32 acres × 0.1 tons/acres = 3.2 tons burned) and
CO season emissions from tumbleweed burning are calculated as follows.
CO season emissions from burning tumbleweeds = tons burned × emission factor
= 3.2 tons × 309 lb CO/ton = 989 lb CO/yr
Burning is normally allowed only on the five weekdays. Season daily emissions were calculated according to the
following example:
Season Daily Emissions (lb) = Seasonal Emissions (lb) =
989 lb CO = 16.48 lb/day or 0.01 tons/day
season operation days
60 days/CO season

3.4.2.3 Burning of Trees
The Maricopa County/University of Arizona Extension Service Agricultural Agents (MCESD, 1993)
estimated the weight of citrus trees to be 500 lb/tree, assuming trees were mature, partially dried and included trunk,
limbs and bulk of roots. In 1999, three burn permits were issued for 4,044 trees. Using the fuel-loading factor
provided by the agricultural agents, the total weight burned is calculated as:
500 lb/tree × 4,044 trees / (2000 lb/ton) = 1,011 tons
No CO emission factors are available for air curtain destructor burning of trees. Citrus tree emission factor
from AP-42’s Open Burning section was used.
CO Emissions from burning trees = tons of wood × emission factor
= 1,011 tons × 81 lb CO/ton = 81,891 lbs/yr or 40.9 tons/yr

1999 CO Emissions Inventory

28

Maricopa County, AZ

Since burn permits for trees are valid for only one month, CO season daily emissions are estimated based
on the permits issued during the winter season. Only one permit was issued in 1999 during December, for 1,040
trees. It is assumed the trees were burned in one month.
Season daily emissions from burning trees =

260 tons × 81 lb CO/ton
5 days/week × 4 weeks/month

= 1053.0 lb/day or 0.53 tons/day

3.4.2.4 Burning for Land Clearance
Land clearance burning is comprised of burning assorted brush, grasses and some tree waste. Tree limbs
and trunks larger than 6" in diameter are required to be removed. The natural vegetation of the area is desert, so it
was assumed the vegetation burned was equal to "unspecified weeds" for choosing fuel-loading and emission
factors. Based on 1999 burn permit information, 6397.16 acres were burned for land clearance, plus 59 piles.
Assuming a pile is equivalent to an acre, as with tumbleweed, the total burned is 6,456.16 acres. Using the AP-42
fuel-loading factor of 3.2 tons/acre for "unspecified weeds," the weight burned was calculated in tons.
Tons of "unspecified weeds" burned for land clearance = 6,456.2 acres × 3.2 tons/acre = 20,660 tons
Total 1999 CO emissions from burning for land clearance = tons burned × emission factor
= 20,660 tons × 85 lb CO/ton
= 1,756,075 lb CO/yr or 878.0 tons CO/yr
Land clearance burning permits are valid for one month. Six land clearance burn permit for a total of 90.12
acres were issued during the CO season in 1999. They were issued between December and February, so it was
assumed the burns occurred within those 3 months.
Tons of CO from burning for land clearance = tons burned × emission factor
= 90.12 acre × 3.2 tons/acre × 85 lb CO/ton
3 months × 5 days/week × 4 weeks/month
= 408.54 lb CO/ day or 0.20 tons CO/day

3.4.2.5 Pest Prevention
Pest prevention burning is comprised of assorted agricultural crops. One permit for 55 acres was issued in
1999. Since the crop wasn’t described, an average fuel-loading factor from “unspecified field crop” and
“unspecified orchard crop” of 1.8 tons/acre was used.
55 acres × 1.8 tons/acre = 99 tons

1999 CO Emissions Inventory

29

Maricopa County, AZ

The emission factor used to calculate emissions from pest prevention burning was averaged from the
above-mentioned categories. The permit, only valid for one month, was issued during the CO season, so assumed all
emissions are in one month.
Total CO emissions from burning for pest prevention = tons burned × emission factor
= 99 tons × 84.5 lb/ton
= 8,365.5 lb/yr = 4.2 tons/yr
1999 CO season daily emissions pest prevention =
8,365.5 lb CO
5 day/wk × 4 wk/month
= 418.28 lb CO/day or 0.21 tons/day

3.4.2.6 Summary of CO Emissions from Managed Burning
Total CO emissions from open burning are obtained by summing the emissions from each type of burning.
The results are shown in Table 3–7.
Table 3–7. Summary of CO Emissions From Managed Burning
Type of Burning
Ditch banks and fence rows (unspecified weeds)
Tumbleweeds
Air Curtain Destructors (citrus trees)
Land clearance (unspecified weeds)
Pest Prevention (unspecified crops)
Totals:

3.5
3.5.1

Annual 1999
CO Emissions (tons/yr)
259.4
33.3
40.9
878.0
4.2
1,215.8

1999 Season Daily CO
Emissions (lbs/day)
0.0
0.01
0.53
0.20
0.21
0.95

Procedures for Estimating CO Emissions from Miscellaneous Area Sources – Other Combustion
Calculation of Emissions from Forest Fires
The Arizona State Land Department provided the number of wildfires that occurred in and around

Maricopa County in 1999. Thirty-three wildfires occurred, burning a total of 192 acres. EPA CO emission factor,
1570 kg/hectare or 1,397.82 lb/acre is used to calculate the emissions (EPA, 1996). The emission factor includes the
fuel-loading factor.
Annual CO emissions = 192 acres × 1,397.82 lb/acre = 268,380 lbs CO/yr
= 134.2 tons CO/yr
Assuming that the fires occurred evenly throughout the year for obtaining CO season day emissions:
CO daily emissions = 268,380 lbs/yr × 0.25
7 × 13

1999 CO Emissions Inventory

= 737.3 lbs CO/day or 0.37 tons CO/day

30

Maricopa County, AZ

3.5.2

Calculation of Emissions from Fireplaces and Wood Stoves
EPA CO emission factors for burning wood in fireplaces and wood stoves are given for tons of wood

burned. To determine CO emissions during 1999 for the Maricopa County nonattainment area, MCESD kept
constant the emissions that were estimated for 1996. This was done due to the Maricopa County Wood Burning
Ordinance that had been put into place September 30, 1994. Although it was anticipated that the ordinance would
create a decrease in emissions, there was no concrete evidence to draw data from. Therefore, it was concluded the
most conservative course would be to assume the emissions stayed constant. For clarity, how emissions were
calculated in the 1996 emission inventory is described below. A few minor errors were discovered in the 1996
inventory, and they were corrected to reflect more accurate emission estimations below. The method for estimating
residential wood consumption described in the procedures document (EPA, May, 1991) was used to estimate CO
emissions in this category.
3.5.2.1 Proportion of Residential Units With Wood-Burning Devices
Survey data collected in Maricopa County in 1996 was used to calculate emissions from residential
woodburning (MAG, 1997). Of the 1,483 surveys, 461 or 31.1% reported having woodburning devices and 295 or
64% used wood. The survey purpose included gathering data on what types of wood are burned and wood-burning
device activity.
Number of Fireplaces:
According to the 1994 demographic data provided by MAG, there were 1,005,529 residential housing units
in the Maricopa County nonattainment area. The survey in 1996 indicated that of the residences surveyed, there
were 398 reported fireplaces out of 461 woodburning devices, or 86.3% (MAG, 1997). Of that 398, 255 or 64.1%
use wood in their fireplaces. The number of residential fireplaces contributing emissions for 1999 is estimated using
the following series of calculations:
# of woodburning devices = 1,005,529 houses × 0.311 fraction houses with woodburning devices
= 312,720 woodburning devices
# of fireplaces

= 312,720 devices × 0.863 fireplaces
= 269,877

# of active fireplaces

= 269,877 fireplaces × 0.641 fraction that burns wood = 172,991

Number of Wood Stoves:
The number of wood stoves was determined similarly. Out of the 461 returned surveys that had
woodburning devices, 16, or 3.5%, had woodstoves and 10 (62.5%) used them to burn wood. The number of
residential woodstoves is estimated using the following series of calculations:
# of woodburning devices = 1,005,529 × 0.311 fraction houses with woodburning devices
= 312,720 woodburning devices

1999 CO Emissions Inventory

31

Maricopa County, AZ

# of woodstoves

= 312,720 devices × 0.035
= 10,945

# of active woodstoves

= 10,945 woodstoves × 0.625 fraction that burns wood = 6,841

Number of Barbecue (BBQ) / Firepits:
The number of BBQ/firepits was determined similarly. Out of the 461 returned surveys that had
woodburning devices, 47, or 10.2%, had firepits and 30 (63.8%) used them to burn wood. The number of residential
firepits is estimated using the following series of calculations:
# of woodburning devices = 1,005,529 houses × 0.311 fraction houses with woodburning devices
= 312,720 woodburning devices
# of firepits

= 312,720 devices × 0.102
= 31,897

# of Active Firepits

= 31,897 firepits × 0.638 fraction that burns wood = 20,351

3.5.2.2 Density and Types of Wood Burned in Maricopa County
Types of wood burned in Maricopa County were also collected during the 1996 survey. Types of wood and
the composite density were calculated and the information is provided in Table 3–8. The weighted average density
was calculated as follows:
Weighted Average Density = (144 × 42.33) + (105 × 29.48) + (103 × 18.8) + (13 × 31.6) + (2 × 40)
367
The composite densities listed for hardwood and softwood are a weighted average of densities listed in Table 3–9.
Table 3–8. Density of Wood Types Used in Wood-burning Devices in Maricopa County
Wood Type
Hardwood (Mesquite and Gambel Oak)
Softwood (Junipers and Ponderosa Pine)
Processed Logs
Miscellaneous (broken furniture and scrap;
used density of Junipers and Ponderosa Pine)
Pellets
Weighted Average Density:

Number of Uses
from Survey
141
105
103
13
2

Composite Density
(lb/ft3)
42.33
29.48
18.8
31.6
40
31.66

The US Forest Service (USFS, 1993) provided MCESD with the following mix of tree species harvested
for firewood in Arizona and sold in the Maricopa County area. The mix and composite wood density of the various
types of wood burned in Maricopa County are shown in Table 3–9. Composite wood density (CWD) combines the
percentage of each type of firewood and its density into a single factor, and is calculated according to the following
formula:
CWD = Σ [ (% wood speciesi ) × (densityi ) ]
1999 CO Emissions Inventory

32

Maricopa County, AZ

Table 3–9. Wood Mix and Composite Wood Density (CWD) for Wood Species Used for Firewood

Tree Species
Both Junipers (Mean)
Ponderosa Pine
Mesquite
Gambel Oak
Pinon Pine and other misc. species

% of Total
Wood
Burned
60 %
20 %
10 %
5%
5%

Density
(lb/ft3)
30.2
26.3
43.7
39.6
31.6

Composite Wood
Density (lb/ft3)
18.1
5.3
4.4
2.0
1.6

3.5.2.3 Volume and Quantity of Wood Burned in Maricopa County
The frequency and quantity of wood burned in fireplaces in the Maricopa County nonattainment area was
also gathered in the 1996 survey (MAG, 1997). Survey respondents were asked the frequency they use their woodburning devices and the number of logs burned for each use. Using the mean range of the survey results for an
average, there are 11.3 uses per household per year and 3.1 logs are burned per use. The estimated number of cords
of wood burned in residential fireplaces in the Maricopa County nonattainment area in 1999 was calculated as:
Quantity of Wood
Burned in Fireplaces
Mass of Wood
Burned in Fireplaces

= 172,991 active fireplaces × 11.3 uses/yr × 3.1 logs/use × 0.17 ft3/log
= 1,030,179 ft3/yr
= 1,030,179 ft3 × 31.57 lb/ft3
= 32,522,751 lbs wood/yr
= 16,261.38 tons wood/yr

Similarly, the amount of wood burned in woodstoves was calculated. Using the mean range of the survey
results for an average, there are 12.8 uses per household per year and 2.3 logs are burned per use.
Quantity of Wood
Burned in Woodstoves = 6,841 active woodstoves × 12.8 uses/yr × 2.3 logs/use × 0.17 ft3/log
= 34,237 ft3
Mass of Wood
Burned in Woodstoves = 34,237 ft3 × 31.57 lb/ft3
= 1,080,862 lbs wood/yr
= 540.43 tons wood/yr
Additionally, the amount of wood burned in firepits was calculated. Using the mean range of the survey
results for an average, there are 7.6 uses per household per year and 2.5 logs are burned per use.
Quantity of Wood
Burned in Firepits
Mass of Wood
Burned in Firepits

1999 CO Emissions Inventory

= 20,351 active firepits × 7.6 uses/yr × 2.5 logs/use × 0.17 ft3/log
= 65,734 ft3
= 65,734 ft3 × 31.57 lb/ft3
= 2,075,222 lbs wood/yr
= 1,037.61 tons wood/yr
33

Maricopa County, AZ

3.5.2.4 Annual CO Emissions from Fireplaces, Woodstoves, and Firepits
The carbon monoxide emission factor for residential fireplaces is 252.6 pounds CO per ton of wood fuel
taken from the updated Section 1.9 of AP-42 (EPA, January 1995), dated October of 1996. Since the amount of
wood burned in fireplaces is estimated to be 17,877.63 tons annually, the total tons of CO from fireplaces is:
Tons of CO from fireplaces = 16,261.38 tons of wood × 252.6 lb/ton
2,000 lb/ton

= 2,053.81 tons CO/yr

The carbon monoxide emission factor for conventional residential wood stoves was calculated as a
weighted average. The weighted average emission factor was based on 80% as conventional, noncatalytic, catalytic,
and masonry stoves and 20% as certified and exempt pellet stoves. The percentages were taken from the survey.
The following calculation shows how the emission factor was calculated by weighted average using AP-42 emission
factors for the various wood stove units (EPA, Oct. 1996).
Wood Stoves CO Emission Factor = 0.8 × [(230.8 + 140.8+ 104.4 + 149)/4] + 0.2 × [(39.4 + 52.2)/2)]
Wood Stoves CO Emission Factor = 125 + 9.16 =134.16 lb/ton
Tons of CO from conventional wood stoves = 540.43 tons × 134.16 lb/ton = 36.25 tons/yr
2,000 lb/ton
For firepits, the emission factor used for fireplaces was used to estimate emissions. It was assumed these
two devices generate similar emissions as they both lack controls.
Tons of CO from firepits = 1,037.61 tons of wood × 252.6 lb/ton = 131.05 tons/yr
2,000 lb/ton

3.5.2.5 CO Season Daily Emissions from Fireplaces and Wood Stoves
It is assumed that 90 percent of the wood burned in Maricopa County is burned in the months of November
through February (121 days). These months represent the holiday season and the coldest months of the year. As
mentioned earlier the use of fireplaces and wood stoves is primarily for aesthetic purposes.
Determining the CO season typical daily CO emissions requires that a Seasonal Adjustment Factor (SAF)
be calculated. This SAF and daily CO emissions are determined based on Section 5.8 and 5.9 of the Procedures
document (EPA, May 1991). Calculations are shown below.
SAF = Peak CO Season Activity) × 12 months
Annual Activity × Peak CO Season months
= 90% × 12 months
100% × 4 months
= 2.7
1999 CO Emissions Inventory

34

Maricopa County, AZ

Fireplace and Woodstove CO Emissions for a Typical CO Season Day
=

Fireplace and Woodstove Annual Emissions × (SAF) / Annual Activity

=

(2,053.81 tons/yr + 36.25 tons/yr) × 2.7 / [(7 days/week) (52 weeks/yr)]

=

15.50 tons CO/day

CO Season Daily Emissions from Firepits
It is assumed that firepits are used evenly throughout the year therefore the annual emissions are divided by
365. The calculation is as follows:
CO Season Daily Emissions = 131.05 tons / 365 = 0.36 tons/day

3.5.3

Calculation of Emissions from Structure, Motor Vehicle, and Vegetation Fires
This section includes emissions from structure, motor vehicle, and vegetation fires. Data was compiled by

a survey to all fire departments in the nonattainment area. A complete list was obtained from the Arizona Department of Emergency Services. The request letter and the survey form that was addressed to the directors of these fire
departments are included in Appendix 3–3. The data requested included the number of structural, vehicle, and
vegetation fires. All of the data supplied were provided on the surveys sent out to the respective fire departments.
Eighteen permits obtained for fire training were included in the number of structure fires. Not all fire departments
returned the survey, so data from a previous survey (1996,1994, 1993, or 1990 in that order of preference) was used.
It is important to note that these emissions may be overstated because the fire data may only represent a partial burn.
The CO emission factor applied to the structure fires can be seen in Table 3–10 below (EPA, July 1999).
Estimates of the material burned are obtained by multiplying the number of structure fires by a fuel-loading factor of
1.15 tons of material per fire (EPA, July 1999).
The automobile fire CO emission factor was developed in California Air Resources Board’s Methods For
Assessing Area Source Emissions (CARB, 1997). It includes a combination of average car body weight and
components, and assumes that 60% of the fires included tires. With the assumption that a car’s components weigh
500 lbs, the following emissions were calculated:
CO Emissions (Body of Automobile) = 4901 fires/yr × 2.5 lbs CO/fire = 12,253 lbs CO/yr
CO Emissions (Components) = 500 lbs/avg. car × 4,901 fires/yr × 60%
= 91,894 lbs CO

The emission factor used for vegetation burned is 85 lb CO/ton with an AP-42 fuel loading factor of 3.2
tons/acre for “unspecified weeds” (EPA, 1995). Vegetation burned includes fences, alley, trash, and yard fires of
accidental occurrence that the fire department has records on. An average size of the fire is unknown so it was
assumed to be equal to a tenth of an acre. The number of fires in the vegetation category was multiplied by 0.1.
1999 CO Emissions Inventory

35

Maricopa County, AZ

No seasonal data are available to estimate a seasonal factor. Fires are assumed to occur equally throughout
a seven-day week. Therefore, the total emissions per year are divided by 365 to estimate a typical day in the CO
season.

Table 3–10. Total CO Emissions from Structure, Automobile, and Vegetation Fires

Type of Fire
Structure
Automobile
Vegetation
Total

3.6

Number of
Fires
3,769
4,901
6,967
15,637

Fuel Loading
Factors
1.15 tons/structure
500 lbs
(avg. wt of car)
3.2 tons/acre
–––––

CO Emission
Factors
60 lb/ton
2.5 lbs/car
125 lbs/ton
85 lb/ton
–––––

Annual CO
Emissions
(tons/yr)
130.0
52.1

Peak CO
Season Emissions
(tons/day)
0.36
0.14

94.7
276.8

0.24
0.74

Summary of All Area Source Emissions
A summary of emissions contributed by area sources is provided in Table 3–11.
Table 3–11. Summary of All Area Source CO Emissions
Report
Section
Area Source Fuel Combustion Category
Stationary Source Fuel Combustion:
3.3.1
Industrial External Natural Gas Combustion
Industrial Internal Natural Gas Combustion
Industrial External Fuel Oil Combustion
Industrial Internal Fuel Oil Combustion
3.3.2
Commercial/Institutional
External Combustion
Internal Combustion
3.3.3
Residential; External Combustion
Waste Disposal, Treatment And Recovery:
3.4.1
On-Site Incineration
3.4.2
Open Burning
Miscellaneous – Other Combustion:
3.5.1
Wildfires
3.5.2
Fireplaces, Wood Stoves, and BBQ/Firepits
3.5.3
Structure, Motor Vehicle, and Vegetation Fires
TOTALS

1999 CO Emissions Inventory

36

Annual CO
Emissions
(tons/yr)

Season Day
CO Emissions
(tons/day)

233.7
46.2
0.4
323.0

0.78
0.15
0.00
1.03

347.1
742.4
289.5

1.20
2.05
0.89

9.2
1,215.9

0.04
0.95

134.2
2,221.1
276.8
5,839.5

0.37
15.86
0.74
24.06

Maricopa County, AZ

3.7

References for Section 3

California Air Resources Board. Emissions Inventory Procedural Manual, Volume III: Methods for
Assessing Area Source Emissions. October 1997.
Maricopa Association of Governments. 1994 Regional PM10 Emission Inventory for the Maricopa County
Nonattainment Area. 1997.
Maricopa Association of Governments. Maricopa County Demographic Information, Ozone and CO NonAttainment Areas, Year 1999. July, 2000.
Maricopa County Environmental Services Department. 1990 Base Year Carbon Monoxide Emission
Inventory. August 1993.
Maricopa County Environmental Services Department. 1996 Carbon Monoxide Periodic Emission
Inventory. October 1999.
U.S. Environmental Protection Agency. AIRS Facility Subsystem Source Classification Codes and
Emission Factor Listing for Criteria Air Pollutants. EPA-450/4-90-003. March 1990.
U. S. Environmental Protection Agency. Compilation of Air Pollutant Emission Factors, Vol. I & II, AP-42,
1995.

U. S. Environmental Protection Agency. Compilation of Air Pollutant Emission Factors, 5th Edition Vol. I &
II, AP-42 Supplements A, B, C, D, and E, October 1996- July 2000.
U.S. Environmental Protection Agency. Introduction to Area Source Emission Inventory Development,
Vol. III, EIIP, August 1996.
U.S. Environmental Protection Agency. Procedures for the Preparation of Emission Inventories for Carbon
Monoxide and Precursors of Ozone, Vol. I. EPA-450/4-91-016. May 1991.
U.S. Environmental Protection Agency. Emission Inventory Requirements for Carbon Monoxide State
Implementation Plans. EPA-450/4-91-011. March 1991.

1999 CO Emissions Inventory

37

Maricopa County, AZ

SECTION 4. NONROAD MOBILE SOURCES
4.1

Introduction and Scope
The nonroad mobile source inventory includes emissions from aircraft, locomotives, diesel equipment, 4-

stroke gasoline equipment, and 2-stroke gasoline equipment. This inventory does not account for aircraft activity at
unpaved airports because the activity is considered insignificant. Coal-burning locomotives are not included because
there are none in the nonattainment area. Emissions from snowplows and snowmobiles were not included because
the Phoenix area does not receive enough snow. Only recreational marine vessels were included, since there aren’t
any navigable bodies of water suitable for goods transportation.
Aircraft emissions were calculated using survey information provided by the airports and incorporating
these data into the EPA’s FAA Aircraft Engine Emissions Database (FAEED). Survey information was also used
for calculating locomotive emissions. Emission estimates for diesel equipment, 4-stroke and 2-stroke gasoline
equipment sources were developed using the Energy and Environmental Analysis, Inc. study prepared for EPA's
Office of Mobile Sources (OMS). Nonroad gasoline equipment includes recreational vehicles, construction equipment, industrial/commercial equipment, lawn and garden equipment, and farm equipment. Nonroad diesel equipment includes construction equipment, industrial/commercial equipment, and farm equipment. These emissions
estimates were adjusted to reflect growth and conditions specific to the Phoenix nonattainment area as explained in
section 4.4. Nonroad emission calculations include 1999 annual and average daily CO.
4.2

Procedure for Estimating Emissions from Aircraft
Emission factors for estimating aircraft emissions were determined using the FAA Aircraft Engine

Emissions Database (FAEED). Airport operations data for 1999 were collected from the airports through surveys
sent by mail. All airports except Stellar Aviation responded, therefore 1996 operation numbers were used for Stellar
Aviation. Table 4–1 shows those general aviation airports included in this inventory and the number of 1999
operations (defined as a landing or a take-off). An LTO is a landing and a take-off cycle, and is used in FAEED to
calculate emissions. Therefore, to obtain LTOs, the number of airport operations is divided by two. The operations
data provided by the airports are included in Appendix 4-1.
4.2.1

Emission Factors
The alternative fleet-average method, outlined in Procedures for Emission Inventory Preparation Volume

IV: Mobile Sources (EPA, 1992) was used to calculate emissions for all types of aircraft. The emission factors are
shown below in Table 4–2. When there was more than one type of engine for a specific aircraft, the engine having
maximum CO emissions at idle was used. Emission factors were then back calculated by taking emission estimates
from FAEED and dividing by LTO cycles. For this method, the emission factors for all unique engines in a certain
aircraft type category were averaged since they were reported together in FAEED.

1999 CO Emissions Inventory

38

Maricopa County, AZ

Table 4–1. General Airports and Operation Data
Airport
Chandler Municipal Airport
Stellar Aviation
Glendale Municipal Airport
Phoenix Goodyear Airport
Luke Air Force Base
Mesa Falcon Field Airport
Deer Valley Airport
Scottsdale Airport
Phoenix Sky Harbor
Williams Gateway Airport
Total

1999 Operations
221,018
60,000
130,055
136,278
168,520
263,988
290,791
230,571
557,458
236,278
2,294,957

1999 LTOs
110,509
30,000
65,028
68,139
84,260
131,994
145,396
115,286
278,729
118,139
1,147,480

Specific air carrier operations in 1999 and aircraft type information for 1998 from Sky Harbor was used for
these emission factors. The air taxi emission factor was determined using aircraft type information in FAEED for
long- and medium-range jets and averaging the emission factors. General aviation emission factors were determined
using the aircraft type information in FAEED for the five different categories of general aviation: single-engine
piston, multi-engine piston, single-engine turboprop, multi-engine turboprop, and helicopters. General military
emission estimates were determined as a fleet average using all military aircraft in FAEED except fighter jets. As
most of the Luke Air Force Base airport operations are F-16’s, those military operation emissions were calculated
using FAEED data for F-16’s. No emission factors were available for the business jet category, so the air carrier
emission factor was used, and these emissions were included under general aviation.
Table 4–2. Aircraft Emission Factors
Aircraft Type
(AMS 22-75-050-000)
Air Carrier
Air Taxi
General Aviation Single-Engine Piston
General Aviation Single-Engine Turboprop
General Aviation Multiple-Engine Piston
General Aviation Multiple-Engine Turboprop
General Military
Military F-16s
Helicopters

4.2.2

Emission Factor
(lbs CO/LTO)
17.25
36.32
25.55
7.87
89.72
18.92
83.87
21.06
5.43

Summary of Aircraft Emissions
The FAEED model was used to generate the emission factors for this inventory. Table 4–3 presents the

annual and daily emissions estimated by aircraft type and airport. For calculating general aviation emissions, the
percentage of each type of aircraft was estimated from information provided by the airports in the MAG Aviation
Air Quality Survey for Airports (MAG, 1994).

1999 CO Emissions Inventory

39

Maricopa County, AZ

Sky Harbor winter activity (October through December) was 26.1% of its total annual activity. Other
airport winter activity was calculated according to percentage of fourth quarter activity, which was provided in the
surveys. Example calculations follow the table.
Table 4–3. Annual and Season Daily 1999 Aviation Emissions

Airport
Chandler Municipal Airport
Deer Valley Airport
Glendale Municipal Airport
Phoenix Goodyear Airport
Luke Air Force Base
Mesa Falcon Field Airport

Phoenix Sky Harbor

Scottsdale Airport
Stellar Aviation
Williams Gateway Airport

Aircraft Type
Air Taxi
General Aviation
Military
General Aviation
Military
Air Taxi
General Aviation
Air Carrier
General Aviation
Military
Air Carrier/Taxi
General Aviation
Military
Air Carrier
Air Taxi
General Aviation
Military
Air Carriers
Air Taxi
General Aviation
Military
Air Taxi
General Aviation
Military
General Aviation
Air Carriers
Air Taxi
General Aviation
Military

Totals

4.2.3

Annual CO
Emissions
(tons/yr)
13.0
1,818.5
1.9
2,294.0
11.4
10.5
515.0
4.8
1,076.7
2.5
22.6
105.8
799.4
0.2
30.1
1,823.6
208.2
1,508.2
388.9
750.4
93.4
65.6
2,109.6
9.6
406.4
4.7
41.9
2,734.6
934.9
17,786.5

Season Day CO
Emissions
(lbs/day)
73
10,242
11
13,964
70
57
2,799
28
6,156
14
125
587
4,432
1
174
10,556
1,205
8,557
2,207
4,258
530
368
11,832
54
2,209
25
223
14,565
4,979
100,292

Examples
Example 1: Phoenix Sky Harbor provided operations data for 1999 and aircraft type information from

1998.
Type
Total Air Carrier
General Aviation
Military

1999 Operations
475,627
77,375
4,456

Air taxi and helicopter operations were included with the air carrier operations. The three monthly reports
provided by the airport separated out air taxi operations. The average percentage of air taxi operations from these
1999 CO Emissions Inventory

40

Maricopa County, AZ

reports was 19%; therefore there are 90,369 air taxi operations. In addition, 7.5%, or 35,672 of reported total air
carrier operations are helicopter operations. Unlike the other airports, the information Phoenix Sky Harbor provided
was sufficient to create an air carrier aircraft-specific model using FAEED. Results are shown in Appendix 4–2.
For the general aviation category, aircraft type information from the MAG Aviation Survey conducted in
1994 was used to split the category into business jets, single-engine piston, multi-engine piston, single-engine
turboprop, and multi-engine turboprop based on percentage of LTOs of each type of aircraft. Operations for 1999
were then further split as follows:
Type
Air Carrier
Air Taxi
Helicopters
General Aviation:
–Business Jet
–Single-engine Piston
–Multi-engine Piston
–Single-engine Turboprop
–Multi-engine Turboprop
Military

1999 Operations
349,586
90,369
35,672
77,375
464
57,412
13,618
0
5,881
4,456

1999 LTO Cycles
174,793
45,184
17,836
38,688
232
28,706
6,809
0
2,941
2,228

4.2.3.1 Phoenix Sky Harbor Air Carrier
Emissions were calculated using the FAEED model by entering data on LTO cycles by aircraft type using
1999 air carrier operations (minus helicopter) and 1998 aircraft type supplied by Phoenix Sky Harbor (Appendix 4–
3). The total air carrier emissions calculated by FAEED was 3,794,209 lb/yr. Dividing 349,586 air carrier
operations from 439,955 total operations, is 79.5%. Multiplying the total emissions by 79.5%, 3,016,396 lbs/yr are
air carrier emissions. Therefore, 20.5% or 777,813 lbs are air taxi emissions. The season day emissions were
calculated by multiplying FAEED output by the 26.1% winter seasonal percentage and dividing by 92 days in the
season.
Phoenix Sky Harbor Air Carrier Emissions from FAEED
Pollutant
lbs/yr
tons/yr
lbs/season day
CO
3,016,396
1,508.2
8,557
For other airports with air carrier operations, an average emission factor was calculated based on the Phoenix Sky
Harbor total air carrier emissions and dividing by LTO cycles:
3,794,209 lb/yr ÷ 219,981 LTOs3 = 17.25 lb CO/LTO
4.2.3.2 Phoenix Sky Harbor Air Taxi
Air taxi emission factors were calculated from FAEED by averaging all long- and medium-range jets in the
database and then dividing by the number of unique engines. Emission factors are shown in Table 4–2. Emissions

1999 CO Emissions Inventory

41

Maricopa County, AZ

for all airports except Phoenix Sky Harbor were calculated by multiplying air taxi LTO cycles by the emission
factors. As discussed above, Sky Harbor taxi and carrier operations were reported together. Therefore, of the total
air carrier emissions calculated by FAEED, 20.5% or 777,813 lbs CO/yr, were air taxi emissions. The season daily
emissions were calculated by multiplying the annual emissions by the winter seasonal percentage (26.1% for
Phoenix Sky Harbor) and dividing by 92 days in the season.
Phoenix Sky Harbor Air Taxi Emissions from FAEED
Pollutant
CO

lbs/yr
777,813

tons/yr
388.9

lbs/season day
2,207

Emissions for General Aviation included helicopters, and used the emission factors derived from FAEED. Military
emissions were calculated using the FAEED emission factor for general military and the reported LTOs.

4.3

Procedure for Estimating Emissions from Locomotives
Chapter 6 of EPA's Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources (EPA,

1992), was followed when estimating locomotive emissions. Railroad operations were separated into three
categories: 1) Class I line haul; 2) Class II and Class III line haul; and 3) yard operations. No Class II or Class III
line haul (locally operated railroads), were operating within the nonattainment area boundaries of Maricopa County
in 1999. Carbon monoxide emissions were calculated from Class I line haul and yard operations data and EPA
emission factors (EPA, 1992, Tables 6–1 and 6–2). Total locomotive emissions in the inventory area were
calculated by summing the emissions for both categories.
Railroads operating within the nonattainment boundaries of the Maricopa County are:
1)

Union Pacific Railroad Company (UP)
Ms. Deb Schafer (402) 271-2358
Room 930
1416 Dodge Street
Omaha, NE 68179

2)

Burlington Northern & Santa Fe Railway Company (BNSF)
Mr. John Chavez (909) 386-4082
740 E Carnegie Drive
San Bernardino, CA 92408-3571

4.3.1

Line Haul Locomotives (AMS 22-85-002-005)
Class I line haul locomotives carry mainly interstate freight and most of the passenger service. Emissions

are calculated by multiplying the amount of fuel consumed by these locomotives in the inventory area by the
appropriate emission factors (EPA, 1992, Table 6–1). UP provided 1999 Gross Tons (GT) and a Fuel Consumption

3

This number is slightly different from the 219,977 LTOs for air carriers and air taxis due to rounding.

1999 CO Emissions Inventory

42

Maricopa County, AZ

Index for all trains scheduled to operate in the nonattainment area of Maricopa County (Appendix 4–4). The
following calculations show how the line haul locomotive emissions were derived.
BNSF provided a Fuel Consumption Index (FCI) of 734 GTM/gal. GTM = Gross Ton Miles.
1999 Gal. Diesel per Line Segment = GT × Length of segment (miles)
FCI
= 37,570,000 GT × 49.0 miles = 2,508,079 gallons diesel/yr
734 GTM/gallon
1999 BNSF line haul locomotive emissions are:
Emissions lbs/year = (annual fuel consumption) × (emission factor)
CO lbs/year = (2,508,079 gallons) × (0.0626 lbs/gallon)
= 157,006 lbs/year
= 78.5 tons/year
The Union Pacific Railway Company (UP) determined fuel consumption and calculated emissions
following the same method as above. Traffic density and fuel consumption index were provided by UP (Appendix
4–4). The 1999 fuel consumption as reported by UP for line haul locomotives in Maricopa County is calculated as
follows:
1999 Gallons of Diesel per Line Segment: = 68,380,000 GT × 413 miles = 39,114,875 gallons diesel/yr
722 GTM/gallon
1999 UP line haul locomotive emissions are:
CO lbs/yr = (39,114,875 gallons) × (0.0626 lbs/gallon)
= 2,448,591 lbs/yr
= 1224.3 tons/yr
Season day emissions were obtained by dividing annual totals by 365. Table 4–5 shows the line haul
locomotive estimates by company for both the year and season day in 1999.
Table 4–4. Summary of Annual 1999 Emissions from Class I Line Haul Locomotives
Company
Union Pacific Railroad Company
Burlington Northern & Santa Fe Railway Company
Totals

4.3.2

CO
tons/yr
1,224.3
78.5
1,302.8

CO
lbs/day
6,709
430
7,139

Yard Locomotives (AMS 22-85-002-010)
Emission calculations for yard locomotives are based on the number of yard/switch locomotives in

operation during 1999. Yard/switch locomotives are primarily responsible for moving railcars within a particular
railway yard. The national average of annual carbon monoxide emissions per yard locomotive (EPA, 1992) is
1999 CO Emissions Inventory

43

Maricopa County, AZ

multiplied by the total number of yard locomotives in operation to calculate emissions in tons per year. UP verified
that four yard locomotives operated in 1999. BNSF verified that twelve yard locomotives operated in 1999.
Therefore, the total number of yard locomotives in Maricopa County is sixteen. Emission calculations for these
sixteen yard locomotives are shown below.
Emissions lbs/year = (# of yard/switch locomotives) × (emission factor lbs/yard locomotive)
CO emissions = 16 locomotives × 7,375 lbs CO
locomotive
= 118,000 lbs/yr
= 59.0 tons/yr
Season day emissions were obtained by dividing the annual total by 365.

4.3.3

Summary of Locomotive Emissions
Total annual and season daily emissions from locomotives in the Maricopa County nonattainment area are

shown in Table 4–5.
Table 4–5. Summary of 1999 Annual and Season Daily CO Emissions from Locomotives
CO
(tons/yr)
1,302.8
0
59.0
1,361.8

Locomotive Type
Line haul, Class I
Line haul, Classes II and III
Yard operations
Total

4.4

CO
(lbs/day)
7,139
0
323
7,462

Gasoline and Diesel Nonroad Equipment
Emissions for this category were calculated by growing 1996 emissions data using EPA’s Economic

Growth Analysis System (E-GAS). These growth factors came from the Economic Growth Analysis System
(EGAS), which was developed for the Reasonable Further Progress (RFP) inventory. EGAS, an EPA economic and
activity forecast model, provides credible growth factors for developing projected emission inventories. The 1999
annual and average season day emissions listed in Appendix 4–7 for each source category were calculated by
multiplying the 1996 calculated emissions with appropriate growth factors. The factors take into account our
specific region and county, and required the input of time, from 1996 to 1999. Arizona agricultural statistics were
used to develop factors for agricultural equipment. See Appendix 4–8 for growth factors used listed by engine type.
The following general equation was used to calculate 1999 emissions:
1999 Emissions = 1996 Emissions × EGAS Growth Factor
Maricopa County Environmental Services Department has taken these emission estimates and made the
following modifications:

1999 CO Emissions Inventory

44

Maricopa County, AZ

1. subtracted emissions applied to the nonattainment area from sources that do not operate in Maricopa County
(snowmobiles and snowblowers);
2. adjusted the engine type split for 2-stroke vs. 4-stroke lawn mowers;
3. adjusted the seasonal activity for all nonroad equipment.
For some of the nonroad equipment, further adjustments to the emission estimates were applied based on
control measures. Oxygenated fuel effects were quantified for gasoline-powered equipment. This was a committed
measure of the MAG 1999 Serious Area CO Plan, “Winter Fuel Reformulated Gasoline with 3.5 Percent Oxygen
Content November 1 through March 31” (MAG, 1999). MAG ran EPA’s CO COMPLEX model, and ascertained a
4.14% reduction in CO emissions from the nonroad gasoline-powered equipment, which was applied to the
emissions. Reductions to nonroad emissions based on new diesel engine standards were considered, however these
new standards did not affect CO emissions in 1999 (EPA, 1998). The benefit assessment for the non-handheld
nonroad engine rule stated that the rule had minimal effect on the CO inventory in nonattainment areas (EPA, 1996).
Therefore, no effects were quantified in the 1999 CO emissions inventory for these two rules.
Another adjustment occurred with the 1996 emissions inventory. With respect to lawn mowers, local data
collected by ADEQ for use in the REOP showed that the 5% to 95% split between 2-stroke and 4-stroke engines
based on the VEOP that was used in the 1996 emissions inventory was inaccurate. In Maricopa County, surveyed
residents indicated the split is 15% 2-stroke to 85% 4-stroke (ADEQ, 1997). The 1996 emissions were adjusted to
reflect this new split, as the 1996 emissions estimates were the basis for the 1999 emissions.
Seasonal data from NEVES were replaced for all nonroad equipment categories. For agricultural
equipment, seasonal percentages were determined using local statistics on crop acreage and tractor activity
(Appendix 4–9). The crop acres were obtained from the 1999 Arizona Agricultural Statistics (AASS, 2000). Data
on tractor activity for various crops were taken from both the 1993–1994 Arizona Vegetable Crop Budgets (U of A,
1993) and the 1994–1995 Arizona Field Crop Budgets (U of A, 1994) since more recent budgets did not contain the
same detailed information. Taking the harvested acres of the principal crops grown in Maricopa County, a weighted
seasonal activity average was calculated using monthly tractor activity per acre. This calculation included 271,400
acres of principal crops for which the following equation was used:

%Winter Activity =

∑ crop acreage × (no. of tractor passes/ac re per season × no. tractor passes/ac re per year)
total crop acreage

For all nonroad equipment other than agricultural equipment, seasonal percentages were taken from
monthly activity fractions listed in the California Air Resources Board (CARB) Documentation of Input Factors for
the New Off-road Mobile Source Emissions Inventory Model (EEA, 1992). The activity levels are provided in
Appendix 4–10. MCESD chose to use these seasonal percentages because they more closely resemble the limited
data available for Maricopa County. For example, the CARB seasonal percentage of lawn and garden equipment

1999 CO Emissions Inventory

45

Maricopa County, AZ

activity for the winter season is 19.1%. In comparison, the NEVES study indicates that only 6% of the lawn and
garden activity occur in the winter based on an analysis of agricultural activity from areas of the country of quite
different climates. The following equation was used to adjust emissions to the new seasonal activity levels.
Emissions_new = (Emissions_old × 0.191) / 0.06
where: Emissions_old

= 1990 NEVES emissions estimates using 6% season adjustment

Emissions_new = 1990 NEVES emissions estimates using 19.1% season adjustment.
This seasonal adjustment was applied to all engines in the NEVES lawn and garden category. The
emission estimates for nonroad equipment are listed in Tables 4–6.
Table 4–6. Summary of all Nonroad Equipment Emissions Within the Nonattainment Area
CO
tons/yr
13,956.1
143,377.2
18,560.6
175,893.8

Type of Equipment
Diesel
4-Stroke Gasoline
2-Stroke Gasoline
Totals

4.5

CO
tons/day
37.64
425.85
56.58
520.07

Summary of All Nonroad Mobile Source Emissions
Table 4-7 provides a summary of all nonroad mobile source emissions.
Table 4–7. Summary of all Nonroad Mobile Source Emissions
CO
tons/yr
17,786
1,362
175,894
195,042

Type of Equipment
Aircraft Activity
Locomotives
Nonroad Equipment
Totals

4.6

CO
lbs/day
100,292
7,462
1,040,140
1,147,894

References for Section 4
Arizona Agricultural Statistics Service. 1999 Arizona Agricultural Statistics. 2000.
Arizona Department of Environmental Quality. Voluntary Early Ozone Plan. 1996.
Arizona Department of Environmental Quality. Reanalysis of the Voluntary Early Ozone Plan. 1997.

Environmental Protection Agency. 40 CFR Part 90: Class I and II Non-handheld New Nonroad Phase 1
Small Spark-Ignition Engines: Revised Carbon Monoxide (CO) Standard; Final Rule. November 13, 1996.
Environmental Protection Agency. 40 CFR Parts 9, 86 and 89: Control of Emissions of Air Pollution From
Nonroad Diesel Engines; Final Rule. October 23, 1998.

1999 CO Emissions Inventory

46

Maricopa County, AZ

Energy and Environmental Analysis, Inc. Methodology to Calculate Nonroad Emission Inventories at the
County and Sub-County Level, Draft Final Report. Arlington, VA. July 1992.
Energy and Environmental Analysis, Inc. Nonroad Engine Emission Inventories for CO and Ozone
Nonattainment Boundaries Phoenix Area. Arlington, VA. 1992.
Maricopa Association of Governments (MAG), “Aviation Air Quality Survey for Airports.” Unpublished
survey data, 1994.
Maricopa Association of Governments. MAG 1999 Serious Area Carbon Monoxide Plan for the Maricopa
County Nonattainment Area. June 1999.
Maricopa County Environmental Services Department. 1996 Periodic CO Emission Inventory. September,
1999.
Maricopa County Environmental Services Department. 1990 Modeling Attainment Demonstration. October
1994.
Radian Corporation. VOC/PM Speciation Data System, version 1.32a. Research Triangle Park, NC.
Santa Fe Railway Company correspondence from John Chavez (April 2001).
Union Pacific Railway Company correspondence from Deb Schaefer (May 2001).
U.S. Environmental Protection Agency, Office of Air and Radiation. Nonroad Engine and Vehicle
Emission Study Report. Washington, D.C. November 1991.
U.S. Environmental Protection Agency. Office of Mobile Sources. Procedures for Emission Inventory
Preparation, Volume IV: Mobile Sources, EPA-450/4-81-026d (revised), Chapters 5 & 6. Ann Arbor, MI 1992.

1999 CO Emissions Inventory

47

Maricopa County, AZ

SECTION 5. ONROAD MOBILE SOURCES

5.1

Introduction
The Maricopa Association of Governments (MAG) prepared the onroad mobile source emission estimates

for the 1999 Periodic Carbon Monoxide Inventory for the Maricopa County Nonattainment Area. This
documentation is divided into nine subsections: Introduction, VMT Estimation Procedure, Speed Estimation
Procedure, CO Season VMT Factor, Emission Factor Estimation Procedure, Summary of CO Emissions From
Onroad Mobile Sources, Quality Assurance Process, References, and Appendices.
Onroad mobile source emission estimates have been calculated for carbon monoxide (CO) for the 1999
Periodic CO Inventory. These onroad mobile source estimates are for the 1872 square-mile CO nonattainment area
within Maricopa County. Emission estimates were calculated for the following vehicle types: light duty gas
vehicles (LDGV), light duty gas truck of gross vehicle weight under 6000 pounds (LDGT1) or over 6000 pounds
(LDGT2), heavy duty gas vehicles (HDGV), light duty diesel vehicles and trucks (LDDV and LDDT), heavy duty
diesel vehicles (HDDV), and motorcycles (MC). Emission factors for these vehicle types were calculated using
MOBILE5a, the current version in a series of models developed by the U.S. Environmental Protection Agency
(EPA) for the purpose of estimating motor vehicle emission factors. The resulting emission factors were multiplied
by the estimates of vehicle miles of travel (VMT) to generate emission estimates.

5.2

VMT Estimation Procedure
MAG prepared the 1999 vehicle miles of travel (VMT) estimates for the carbon monoxide nonattainment

area. The source of data for these estimates is the revised 1999 Highway Performance Monitoring System (HPMS)
data (see Appendix 5-1) submitted to the U.S. Department of Transportation, Federal Highway Administration
(FHWA) by the Arizona Department of Transportation (ADOT) in April 2001. ADOT initially submitted 1999
HPMS data to FHWA in August 2000. A revised version, incorporating improved traffic counts on the state
highway system, was submitted in April 2001. The contact person for the VMT estimates is Cathy Arthur (602-2546300).
Each year, MAG coordinates the collection of HPMS data, including the annual average daily traffic
(AADT) estimates for HPMS sample sections which are utilized to develop HPMS VMT estimates. ADOT
provides the AADT for the state highway system routes including interstates, urban freeways, and principal arterials
in Maricopa County. ADOT merges the Maricopa County data with information from other Arizona counties to
create the statewide HPMS data set submitted to FHWA each year.

1999 CO Emissions Inventory

48

Maricopa County, AZ

Arizona’s HPMS database file contains a number of data elements that describe general roadway
characteristics and use for every non-local roadway within the state. All non-local roadways have been divided into
section records that are 0.3 to 10 miles in length, in accordance with HPMS criteria. Such roadway segments are
called HPMS “universe” section records. HPMS contains additional data elements that provide more detailed
operational and performance information on a randomly-selected subset of the file’s 10,000+ universe records.
These more detailed records containing additional highway attributes are known as “sample panels” or “sample
sections.” The VMT estimates which ADOT submits to FHWA each year are generated from HPMS universe data
for all interstates, urban freeways, and principal arterials. Sample section data are expanded to estimate VMT on all
other non-local systems.
VMT on local streets in the urbanized portion of the modeling area is estimated using traffic counts
collected on 50 randomly-selected local streets in June-July of 1994. These counts resulted in an AADT of 587 for
local roads in the urbanized area. To calculate VMT, this AADT was applied to local road mileage in 1994 obtained
from the Maricopa County street centerline coverage. In 1994, an AADT of 150 was assumed for local roads which
are inside the PM-10 (particulates of size ten microns or less) nonattainment area, but outside the urbanized area
boundary. Since 1994, the AADTs on local streets have been increased annually on the basis of the rate of
population growth in Maricopa County; the number of center line miles of local streets is updated annually by the
local jurisdictions in Maricopa County. VMT for the CO nonattainment area, based on the revised 1999 HPMS data
ADOT submitted to FHWA in April 2001, is summarized by area type and facility type in Table 5-1. Area types are
a function of population and employment density as described in Table 5-1. Facility types represent the
characterizations of different roadway types such as capacity, design, and purpose (i.e. serving regional or
neighborhood traffic).
The revised 1999 HPMS System Length and Daily Vehicle Travel for Individual Urbanized Areas (in
Appendix 5-1) was submitted to FHWA by ADOT in April 2001. This table reported a 1999 average daily VMT for
the Phoenix urbanized area of 55.072 million. In comparison, the 1999 urbanized area VMT for the CO
nonattainment area used in the periodic emissions inventory is 54.521 million. The one percent difference between
these estimates is attributable to small sections of the Phoenix urbanized area (i.e. Apache Junction) which are not
located in the CO nonattainment area. The HPMS System Length and Daily Travel, Donut Area Data for Individual
NAAQS Nonattainment Areas, (in Appendix 5-1), reported a revised 1999 VMT for the “donut” area of 5.174
million. The “donut” area is an HPMS term referring to the area inside the PM-10 nonattainment area, but outside
the Phoenix urbanized area boundary. The VMT for the CO nonattainment area is 72 percent of the HPMS “donut”
area VMT or 3.725 million. The factors (i.e. 99 percent for the urbanized area and 72 percent for the donut area)
used to determine the allocation of HPMS VMT to the CO nonattainment area were derived from the report,
Maricopa Association of Governments Highway Performance Monitoring System Update, January 1995. These
same factors were also used to derive VMT for the CO tracking area in Chapter Three of the MAG 1999 Serious
Area Carbon Monoxide Plan for the Maricopa County Nonattainment Area, June 1999. It is important to note that
the 1999 HPMS daily VMT for the CO nonattainment area is within one percent of the 1999 VMT estimated by the

1999 CO Emissions Inventory

49

Maricopa County, AZ

MAG travel demand models for the Serious Area CO Plan. The total 1999 daily VMT for the urbanized and
“donut” areas in the CO nonattainment area is 58.247 million, as shown in Table 5-1.
The VMT by facility type in Table 5-1 was derived from the 1999 HPMS data, while the distribution by
area type was derived from 1998 traffic counts. These counts were assigned to a 1998 highway network using MAG
travel demand models. The output of this assignment was evaluated using Geographic Information Systems (GIS)
to obtain VMT by area type and facility type for the Phoenix urbanized and “donut” areas. The area type
distributions from the MAG traffic assignment were applied to the 1999 HPMS VMT estimates by facility type for
the urbanized and “donut” areas to create Table 5-1.
Although HPMS includes vehicle mix data for urban and rural areas of Arizona, there are insufficient
classification stations in the Phoenix urbanized area to justify use of this information in calculating VMT by vehicle
class. In addition, the HPMS vehicle class data do not discriminate between gas and diesel vehicles. Therefore,
MOBILE5a model defaults, representing the fraction of total VMT for each vehicle class, were applied to VMT
estimates for each facility type and area type in Table 5-1.
Table 5–1. 1999 HPMS VMT by Area and Facility Type for the CO/Ozone Nonattainment Area
(Annual Average Daily Traffic)
AREA TYPE *
Facility Type

1
1,277,694

2
8,275,357

3
5,740,120

4
2,197,672

5
686,975

Total
18,177,818

Principal Arterial /
Minor Arterial

509,464

9,637,550

10,924,791

5,331,263

2,272,805

28,675,873

Collector

261,621

2,943,882

1,374,465

652,983

823,809

6,056,760

Local

59,642

1,823,506

2,191,031

1,088,309

173,623

5,336,111

Total:

2,108,421

22,680,295

20,230,407

9,270,227

3,957,212

58,246,562

Interstate/Freeway

* Area Type = f(DENSITY of a planning district) where:
DENSITY = (Population + 2 × Employment) / Area
For Area Type 1, DENSITY = 20,001+
For Area Type 2, DENSITY = 10,001–20,000
For Area Type 3, DENSITY = 5,001–10,000
For Area Type 4, DENSITY = 1,001–5,000
For Area Type 5, DENSITY = 0–1,000
** Collectors are minor streets that connect a neighborhood to a half-mile or mile arterial.

5.3

Speed Estimation Procedure
MAG prepared the average daily speeds for the 1999 periodic carbon monoxide emissions inventory. The

average daily speeds were obtained from an EXPLORA emissions model run for 1999. EXPLORA integrates travel

1999 CO Emissions Inventory

50

Maricopa County, AZ

demand modeling output and FORTRAN-based emissions processing programs into a planning tool that may be
applied at the subregional or regional level to examine transportation and related air quality issues.
The peak and off-peak speeds used in the EXPLORA volume to capacity (V/C) versus speed table were
derived from the MAG study, 1993 Study of Travel Speed and Delay in the MAG Region, January 1995. The peak
and off-peak speeds obtained from this study were coded into the link records for each road or street segment for
which speed data were collected. A program called SPDVAL was then run to obtain the peak and off-peak speeds
by area type and facility type. Freeways and arterials were the only two facility types with a sufficient sample size
to obtain speeds by area type.
These peak and off-peak freeway and arterial speeds were used to revise the EXPLORA V/C versus speed
table. Speeds for other minor facility types were derived from the MAG study, 1986 Phoenix Urbanized Area
Travel Speed Study, October 1986. MAG plans to conduct a new speed study in FY 2002. It is anticipated that the
results of this speed study will be incorporated into the next periodic inventory analysis.
1999 link-based traffic volumes and capacities output by the MAG travel demand model were input to
EXPLORA to obtain average daily speeds by area type and facility type. The final speeds used in constructing the
1999 periodic emissions inventory are presented in Table 5-2.
Table 5–2. Average Daily Speeds For the 1999 Periodic Emissions Inventory (in mph)
Facility Type

AREA TYPE *
3
4
57.1
61.3

Interstate/Freeway

1
52.1

2
6.8

5
63.3

Principal Arterial / Minor Arterial

27.0

28.0

30.4

33.8

42.0

Collector

24.0

24.3

25.6

28.1

27.7

Local

15.0

20.0

5.0

25.0

30.0

*Area Type = f(DENSITY of a planning district) where:
DENSITY = (Population + 2 × Employment) / Area
For Area Type 1, DENSITY = 20,001+
For Area Type 2, DENSITY = 10,001–20,000
For Area Type 3, DENSITY = 5,001–10,000
For Area Type 4, DENSITY = 1,001–5,000
For Area Type 5, DENSITY = 0–1,000

5.4

CO Season VMT Factor
The Maricopa Association of Governments (MAG) developed the CO season VMT factor for the carbon

monoxide periodic emission inventory. Since the VMT utilized in the periodic emissions inventory is based on
annual average daily traffic (AADT), it is necessary to examine the relationship between AADT and monthly traffic
variations and correct for any differences.
1999 CO Emissions Inventory

51

Maricopa County, AZ

The carbon monoxide season for the Maricopa County nonattainment area occurs from October through
April. The peak CO season reflects the three consecutive months when peak CO concentrations occur. For
consistency with the 1996 Base Year Carbon Monoxide Inventory, the three consecutive months selected were
November 1999 through January 2000, in accordance with EPA guidance.
The CO season VMT factor was developed from 1993 automated traffic recorder (ATR) data collected at
five sites located in the CO nonattainment area. Although there were eight active ATRs, only five collected twelve
months of continuous data in 1993. The 1993 traffic count factors for the winter months for each ATR are provided
below. These represent the ratio of the average monthly counts to the annual average counts.
Traffic Count Factors by Month
November
0.99555

ATR 24 - Grand Ave @ Glendale Ave

December
0.95513

January
0.99076

ATR 30 - Indian School @ 47th Dr

0.96552

1.03016

1.00377

ATR 31 - Central Ave @ Montebello

1.02748

1.01715

0.93712

ATR 32 - Lincoln Dr @ 23rd St

1.01324

1.02714

0.97627

ATR 34 - Squaw Peak Pkwy @ Crittendon

1.01396

0.99365

0.95205

Averages:

1.00315

1.00465

0.97199

The average (arithmetic mean) of the monthly factors across all five stations is 0.99326. When this factor
is applied, the resultant 1999 average daily VMT by facility type for the CO season is illustrated in Table 5-3.
Although shopping trips increase during November and December, the reduction in work and school trips during the
holidays more than offset this increase.
Table 5–3. Average Daily VMT During 1999 Carbon Monoxide Season (November 1999–January 2000)
Area Type *
Facility Type
1
2
3
4
5
Total
Interstate/Freeway

1,269,082

8,219,581

5,701,432

2,182,860

682,345

18,055,300

Principal Arterial /
Minor Arterial

506,030

9,572,593

10,851,158

5,295,330

2,257,486

28,482,598

Collector

259,858

2,924,040

1,365,201

648,582

818,257

6,015,937

Local

59,240

1,811,216

2,176,263

1,080,974

172,453

5,300,146

Total:

2,094,210

22,527,430

20,094,054

9,207,746

3,930,540

57,853,980

* Area Type = f(DENSITY of a planning district) where:
DENSITY = (Population + 2 × Employment) / Area
For Area Type 1, DENSITY = 20,001+
For Area Type 2, DENSITY = 10,001–20,000
For Area Type 3, DENSITY = 5,001–10,000
For Area Type 4, DENSITY = 1,001–5,000
For Area Type 5, DENSITY = 0–1,000

1999 CO Emissions Inventory

52

Maricopa County, AZ

5.5

Emission Factor Estimation Procedure

5.5.1

Emission Factor Model
CO vehicle exhaust emission factors were calculated using MOBILE5a. MOBILE5a is a current version in

a series of models developed by EPA for the purpose of estimating motor vehicle emission factors for carbon
monoxide. The resulting emission factors were combined with VMT estimates to produce emission estimates for
carbon monoxide. The MOBILE5a runs were executed by the Maricopa Association of Governments. The contact
person for the MOBILE5a emission estimates is Roger Roy (602-254-6300).
The following three MOBILE5a runs were executed for carbon monoxide for a typical day (24-hour
period) during the three-month period of November through January:
1.

Enhanced inspection/maintenance (I/M240) program in place with no exemption for current +4 model
year vehicles. For the purposes of this analysis, the current +4 model years reflect the current model
(2000) and the previous four model years (1996-1999).

2.

I/M240 program with exemption for current +4 model year vehicles.

3.

No I/M program in place.

The emission factors estimated with these runs were combined to reflect the actual proportions of vehicles
subject to the specified levels of inspection. The term "I/M vehicles" denotes vehicles which are required to
undergo an emission test and/or inspection under the Arizona Vehicle Inspection/Maintenance Program. It is
important to note that participation in the I/M program is required for all vehicles registered in the nonattainment
area, with the exception of certain model year and vehicle types. However, it is assumed that of the vehicles which
are of an age and type subject to an I/M program only 91.7 percent of the vehicles operating within the
nonattainment area participate in the I/M program. The remaining 8.3 percent do not participate in the program.
These percentages reflect the implementation of the control measures “Tougher Registration Enforcement” and
“Expansion of Area A Boundaries”, described in the MAG 1999 Serious Area Carbon Monoxide Plan for the
Maricopa County Nonattainment Area, MAG, June 1999. In the absence of any additional data, this percentage split
is assumed to apply directly to VMT as well. Specifically, the base fraction of vehicles participating in the I/M
program in the Serious Area CO Plan (89.6 percent) is increased by 2.0 percent reflecting the full implementation of
“Tougher Registration Enforcement” and by 0.1 percent reflecting partial implementation of “Expansion of Area
A”.
In order to accurately reflect the state of the I/M program in the modeling area, several MOBILE5a runs
were performed and the emission factors from those runs were weighted together. Two MOBILE5a runs which
reflected I/M and one which reflected no I/M were performed. The weighting of one I/M and one non-I/M run is

1999 CO Emissions Inventory

53

Maricopa County, AZ

explained in the previous paragraph. The weighting of two I/M runs is the result of a limitation to the MOBILE5a
model. MOBILE5a does not accurately model a change in the variable “last model year tested” if the change in the
“last model year tested” value occurred within the current I/M cycle.
This limitation is relevant because the current +4 model year vehicles were exempted from the I/M
program beginning in August 1998. This modeling effort reflects the three-month period of November 1999
through January 2000. During the middle of these three months, December 1999, the exemption of current +4
vehicles from testing had been implemented 16 months earlier in the current 24-month cycle. For this reason, the
change had effectively propagated through two-thirds (16 months/24 months) of the I/M240 fleet. The exemption of
the recent model years was modeled through a weighting of two MOBILE5a runs, one reflecting the exemption of
the current +4 model years (in this case, model years 1996-2000) and one which did not include that exemption.
Refer to Appendix 5-2 for portions of the actual input and output files and a spreadsheet showing the
emission factor calculations.

5.5.2

Development of Model Inputs
The inputs to MOBILE5a are grouped into eight categories: Control Section, I/M Descriptive Input,

Alternative I/M Credit Files, ATP Descriptive Input, Pressure Test Descriptive Input, Scenario Records, Local Area
Parameter, and Oxygenated Fuels Descriptive Record. The input values used in the above described MOBILE5a
runs are specified and explained below.

5.5.2.1 Control Section
1.

TAMFLG=1 indicates that MOBILE5a default tampering rates were used as recommended in the User's

Guide.
2.

SPDFLG=1 indicates that user-supplied speeds were applied to all vehicle types. Refer to item 3 in the

Scenario Records section for development of input.
3.

VMFLAG=1 indicates that MOBILE5a default VMT mix (national average) was used; this is due to the

difficulty in obtaining accurate mileage accumulation rates by vehicle class. This parameter specifies the fraction of
total VMT that is accumulated by each of the eight vehicle classes.
4.

MYMFLG=3 indicates that user supplied registration distributions and MOBILE5a annual mileage

accumulation rates were used, as recommended by the User's Guide. The vehicle registration distributions
incorporated into this analysis are derived from registration data for 1999 provided by the Arizona Department of
Transportation.

1999 CO Emissions Inventory

54

Maricopa County, AZ

5.

NEWFLG=1 indicates that MOBILE5a default basic exhaust rates were used, as recommended by the

User's Guide.
6.

IMFLAG=1 and 3 means that one of two flags was set in the three MOBILE5a runs that were executed.

Two runs assumed that two I/M programs were in place, and the other run assumed that no I/M program was in
place. The emission factors obtained from the runs were then weighted together.
7.

ALHFLG=1 indicates that no additional correction factors were input. Correction factors were not required

per the User's Guide.
8.

ATPFLG=1 or 5 were input to indicate that one run involved no anti-tampering program and no pressure

test and two runs included both an anti-tampering program and pressure test.
9.

RLFLAG=5 indicates that refueling emissions were zeroed-out. Refueling emissions do not contribute to

CO emissions.
10.

LOCFLG=1 indicates that a separate Local Area Parameter (LAP) record was entered for each scenario of

the MOBILE5a runs. The area type for which emission factors were being calculated was specified within each
LAP record.
11.

TEMFLG=1 indicates that MOBILE5a internally calculated the temperatures to be used in the correction of

emission factors based upon the minimum and maximum daily temperatures provided in the LAP record. This
option is recommended by the Users' Guide. Note: The ambient temperature input within each scenario record is
overridden by the temperature internally calculated by the model.
12.

OUTFMT=6 means outputs were in a spreadsheet format to facilitate subsequent calculations.

13.

PRTFLG=2 indicates that calculations were performed for CO emission factors only.

14.

IDLFLG=1 indicates that no idle emission factors were calculated. Idle emission factors are not necessary

for this inventory.
15.

NMHFLG=4; note: this flag is not applicable for carbon monoxide runs.

16.

HCFLAG=3; note: this flag is not applicable for carbon monoxide runs.

5.5.2.2 I/M Descriptive Input Record
The I/M240 inputs used for the 1999 periodic inventory are consistent with those used for the projected
modeling inventory in the Serious Area CO plan for the 2000 base case (MAG, 1999) with minor adjustments made
to the waiver rates and last model year tested.
1.

PROGRAM START YEAR=77

1999 CO Emissions Inventory

55

Maricopa County, AZ

2.

STRINGENCY LEVEL=28% indicates that 28 percent of pre-1981 model year passenger cars or pre-1984
light duty trucks are expected to fail the initial I/M test in a given testing cycle.

3.

FIRST MODEL YEAR=67 or 81 for the basic I/M or I/M240 program.

4.

LAST MODEL YEAR=20 or 95

5.

WAIVER RATE for PRE-1981 MODEL YEAR VEHICLES=1% indicates that one percent of pre-1981
model year vehicles which fail the initial I/M test will receive a waiver.

6.

WAIVER RATE for 1981 and LATER MODEL YEAR VEHICLES=2% indicates that two percent of
1981 and later model year vehicles which fail the initial I/M test will receive a waiver.

7.

COMPLIANCE RATE=97% indicates that 97 percent of the vehicles registered in the modeling area
complete the I/M process to the point of either passing the I/M test or receiving a valid waiver.

8.

PROGRAM TYPE=1 for centralized program.

9.

INSPECTION FREQUENCY=1 or 2 for annual inspection frequency for the basic I/M or biennial
frequency for the I/M240 program.

10.

VEHICLE TYPES SUBJECT TO INSPECTIONS= 2222 or 2221 indicates that LDGV, LDGT1, LDGT2,
and HDGV are all subject to inspection for the basic I/M program but that HDGVs are exempt from the
I/M240 program.

11.

TEST TYPE=3 or 4 for a loaded idle basic I/M test or a transient I/M240 test.

12.

CUTPOINTS=1 or 2 indicates that MOBILE5a default cutpoints were used for the basic I/M program but
that non-default cutpoints were used for the I/M240 test.

13.

ALTERNATE I/M CREDITS INPUT BY USER=11 or 22 indicates that MOBILE5a default credits were
used for Tech I-II and Tech IV+ vehicles for the basic I/M program but that alternate I/M credits were used
for the I/M240 program.

14.

USER SUPPLIED CUTPOINTS=2.00 30.0 3.00 indicates the cutpoints in grams per mile chosen for
HC, CO, and NOx respectively. These cutpoints are used only for the enhanced I/M240 program.

5.5.2.3 Alternative I/M Credit Files
Since the I/M240 cutpoints in use in the nonattainment area are not a standard set of cutpoints built into the
MOBILE5a program, an alternative set of cutpoints was developed by Radian International for use in onroad
1999 CO Emissions Inventory

56

Maricopa County, AZ

modeling. These alternative cutpoint credit files were further adjusted by MAG using the EPA Remote Sensing
Utility to account for the implementation of a remote sensing program, which was still in place during the period
modeled. A remote sensing program is a form of vehicle emissions inspection which measures instantaneous
vehicle emissions during actual driving conditions. The credit files listed below are in ASCII format and contain a
very large and nondescript array of numbers used to apply emissions reductions credits.
TECH I-II VEHICLES CREDIT FILE= f:\mobile5a\tech12.1me
TECH IV+ VEHICLES CREDIT FILE= f:\mobile5a\imdata.1me

5.5.2.4 ATP Descriptive Input Record
The anti-tampering program (ATP) inputs are consistent with those used for the base case Serious Area CO
SIP inventory for 2000.
1.

PROGRAM START YEAR=87 indicates that the ATP program began in 1987.

2.

FIRST MODEL YEAR=75 indicates that the ATP program includes vehicles of model year 1975 and later.

3.

LAST MODEL YEAR=80 indicates that vehicles of model year 1981+ are exempt from the ATP program
because they are subject to the I/M240 program.

4.

VEHICLE TYPES SUBJECT TO INSPECTIONS= 2222 indicates that LDGV, LDGT1, LDGT2 and
HDGV are all subject to inspection.

5.

PROGRAM TYPE=1 for centralized program.

6.

INSPECTION FREQUENCY=1 for annual inspection frequency.

7.

COMPLIANCE RATE=97%

8.

INSPECTIONS PERFORMED=22111222 indicates that the following ATP inspections are performed: air
pump system, catalyst, evaporative control system, PCV system, and gas cap tests; and that the EGR
system, fuel inlet restrictor, and tailpipe lead deposit tests are not performed.

5.5.2.5 Pressure Test Descriptive Input Record
The pressure test inputs are consistent with those used for the base case Serious Area CO SIP inventory for 2000.
1.

PROGRAM START YEAR=96 indicates that the pressure test began in 1996.

2.

FIRST MODEL YEAR=81 indicates that the pressure test includes vehicles of model year 1981 and later.

1999 CO Emissions Inventory

57

Maricopa County, AZ

3.

LAST MODEL YEAR=20 or 95

4.

VEHICLE TYPES SUBJECT TO INSPECTIONS= 2221 indicates that LDGV, LDGT1, and LDGT2 are
all subject to inspection. HDGV are exempt from the pressure test.

5.

PROGRAM TYPE=1 for centralized program.

6.

INSPECTION FREQUENCY=2 for biennial inspection frequency.

7.

COMPLIANCE RATE=97%
5.5.2.6 Scenario Records

1.

REGION=1 indicates the geographic area modeled was low altitude.

2.

CALENDAR YEAR=00; was input because the applicable three-month period for this inventory is
November, December, 1999 and January, 2000. To be consistent with the User's Guide, the calendar year
2000 was chosen to model conditions representative of the applicable period.

3.

SPEED; a scenario utilizing the speed for each combination of facility and area type was executed (see
Table 5-2). Speed values were input for interstates/freeways, principal/minor arterials, collectors, and local
roads. These speed values were derived from the 1993 Study of Travel Speed and Delay in the MAG
Region.

4.

AMBIENT TEMPERATURE= 63.7 degrees Fahrenheit; the ambient temperature was calculated from data
provided by MCESD (see Appendix 5-3) in accordance with the temperature guidance and input in each
scenario. It is important to note that this temperature is not actually utilized by the model due to
TEMFLG=1. Refer to item 11 in the Control Section for additional information.

5.

OPERATING MODES=20.6, 27.3, 20.6; the MOBILE5a (FTP) standard operating mode fractions were
used as recommended by the User's Guide. These values represent percent cold-start/non-catalyst VMT
(PCCN), percent cold-start/catalyst VMT (PCCC), and percent hot-start/catalyst VMT (PCHC)
respectively. The other relevant operating mode conditions of stabilized/catalyst VMT, stabilized/noncatalyst VMT, and hot-start/non-catalyst VMT are derived internally by MOBILE5a using PCCN, PCCC,
PCHC.

6.

MONTH OF EVALUATION=Blank indicates that January was the month being evaluated.

5.5.2.7 Local Area Parameter Record
1.

SCENARIO NAME; An area type and facility type were indicated for each scenario (speed).

1999 CO Emissions Inventory

58

Maricopa County, AZ

2.

ASTM VOLATILITY CLASS was left blank because the RFGFLG (Item 8 below) was set to indicate no
reformulated gasoline. Rather, actual monitored fuel data for the modeling period was input to the model,
as described in number eight.

3.

MINIMUM and MAXIMUM DAILY TEMPERATURE=45 and 73 degrees Fahrenheit; for consistency,
the same daily minimum and maximum temperatures used in preparing the 1990 Base Year CO Inventory
were also used for the 1999 periodic inventory. The temperatures were calculated by the Maricopa County
Environmental Services Department (MCESD) using EPA-recommended procedures (see Appendix 5-3).

4.

"PERIOD 1" RVP= 8.43; to determine these inputs, RVP data were obtained from the Arizona Department
of Weights and Measures for the applicable period (see Appendix 5-4).

5.

"PERIOD 2" RVP = 8.43; the RVP for period 2 is the same as for period 1, with a start year of 2020. The
period 2 RVP is in effect being dummied out because only one calendar year is being modeled.

6.

OXYFLG=2 indicates the effects of oxygenated fuels were modeled in order to represent actual conditions
that existed in the applicable period.

DSFLAG=2 indicates that locally derived diesel sales fractions were used. The diesel sales fractions immediately
follow the Oxygenated Fuels Descriptive Records.
RFGFLG was left blank, indicating that the reformulated gasoline flag was set to indicate no reformulated gasoline.
Rather than permitting MOBILE5a to set the local gasoline RVP and oxygenate content to reflect default values for
Federal RFG, measured gasoline RVP and oxygenate data, provided by the Arizona Department of Weights and
Measures for the appropriate time period, were input to MOBILE5a.

5.5.2.8 Oxygenated Fuels Descriptive Record
1.

MTBE BLEND MARKET SHARE= 0%; The MTBE market share fraction for the applicable period was
obtained from the Arizona Department of Weights and Measures.

2.

ALCOHOL BLEND MARKET SHARE=100%; The ethanol market share fraction for the applicable
period was obtained from the Arizona Department of Weights and Measures.

3.

AVERAGE OXYGEN CONTENT OF ETHER BLEND FUELS=0.0%; to determine this input, testing
data were obtained from the Arizona Department of Weights and Measures for the applicable period (see
Appendix 5-4).

4.

AVERAGE OXYGEN CONTENT OF ALCOHOL BLEND FUELS=3.4%; to determine this input, testing
data were obtained from the Arizona Department of Weights and Measures for the applicable period (see

1999 CO Emissions Inventory

59

Maricopa County, AZ

Appendix 5-4). Note that these data do not reflect the entire CO season, but only the period considered in
this modeling effort, November 1999 through January 2000.
5.

RVP WAIVER SWITCH=1 indicating a 1 psi exemption was not utilized. This is because actual RVP data
was input to the model.

5.5.3

Model Outputs
MOBILE5a was executed with the inputs described above to obtain composite emission factors in grams

per mile (g/mi) for exhaust CO. These values were obtained for the eight vehicle classes described in the
Introduction for the various speeds as described in item three of the Scenario Records section. The emission factors
generated for the 1999 carbon monoxide season are presented in the following section. Representative output runs
are contained in Appendix 5-2. These values were subsequently used in developing emission estimates.

5.5.5

Summary of Emission Factors

Refer to Appendix 5-2 for the emission factors developed for CO for each facility and area type.

5.5.6

Emission Estimates
MOBILE5a was used to generate CO emission factors for vehicle class, facility, and area type. Daily VMT

for the CO season (Table 5-3) was then multiplied by the VMT mix by vehicle class and the appropriate CO
emission factor (Appendix 5-2) to estimate CO emissions on a kilogram per day (kg/day) basis. An example
calculation is given below:
700,491
(DVMT)

×

3,379
(CO emissions
in kg/day)

0.634
(VMT
Mix)
×

×

1 lb
0.4536 kg

7.609
(CO Emission
Factor, in g/mi)
=

÷

1,000
(grams / kg)

=

3,379
(CO emissions
in kg/day)

7,449
(CO emissions
in lbs/day)

Table 5-4 shows daily VMT data, associated speed estimates, MOBILE5a emission factors, and the
calculated onroad emissions for each vehicle class, facility type, and area type.

1999 CO Emissions Inventory

60

Maricopa County, AZ

Table 5–4. CO Emissions by Vehicle Class, Area Type, and Facility Type
Facility
Type

Vehicle
Class

INTERSTATE,
FREEWAY,
& EXPRESSWAY

LDGV
with VMT
mix of
60.5%
LDGT1
with VMT
mix of
17.6%
LDGT2
with VMT
mix of
8.6%
HDGV
with VMT
mix of
3.8%
LDDV
with VMT
mix of
0.2%
LDDT
with VMT
mix of
1.4%
HDDV
with VMT
mix of
7.4%
MC
with VMT
mix of
0.5%

1999 CO Emissions Inventory

Area Speed
Type (mi/hr)
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3
1
52.1
2
56.8
3
57.1
4
61.3
5
63.3

Emission
Factor
(grams/mi)
4.611
5.572
5.732
7.973
9.040
6.352
7.836
8.084
11.546
13.196
7.705
9.708
10.041
14.714
16.939
11.947
13.236
13.344
15.279
16.521
0.751
0.791
0.795
0.863
0.908
0.724
0.763
0.766
0.833
0.876
5.334
5.620
5.646
6.134
6.454
7.126
10.215
10.730
17.937
21.369

61

DVMT
(miles)
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345
1,269,082
8,219,581
5,701,432
2,182,860
682,345

Emissions
(lb/day)
7,800.0
61,042.9
43,557.3
23,197.6
8,221.8
3,130.9
25,016.3
17,900.7
9,789.1
3,497.1
1,855.8
15,143.9
10,865.1
6,095.4
2,193.6
1,271.5
9,123.2
6,380.0
2,796.9
945.3
4.2
28.7
20.0
8.3
2.7
28.4
193.8
134.9
56.2
18.5
1,105.4
7,543.6
5,256.8
2,186.6
719.2
99.8
926.4
675.0
432.0
160.9

Emissions
(kg/day)
3,538.1
27,689.1
19,757.6
10,522.5
3,729.4
1,420.2
11,347.4
8,119.8
4,440.3
1,586.3
841.8
6,869.3
4,928.4
2,764.9
995.0
576.7
4,138.3
2,894.0
1,268.7
428.8
1.9
13.0
9.1
3.8
1.2
12.9
87.9
61.2
25.5
8.4
501.4
3,421.8
2,384.5
991.8
326.2
45.3
420.2
306.2
196.0
73.0

Maricopa County, AZ

Table 5–4. CO Emissions by Vehicle Class, Area Type, and Facility Type (continued)

Facility
Type

Vehicle
Class

PRINCIPAL
ARTERIALS
&
MINOR
ARTERIALS

LDGV
with VMT
mix of
60.5%
LDGT1
with VMT
mix of
17.6%
LDGT2
with VMT
mix of
8.6%
HDGV
with VMT
mix of
3.8%
LDDV
with VMT
mix of
0.2%
LDDT
with VMT
mix of
1.4%
HDDV
with VMT
mix of
7.4%
MC
with VMT
mix of
0.5%

1999 CO Emissions Inventory

Area Speed
Type (mi/hr)
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0
1
27.0
2
28.0
3
30.4
4
33.8
5
42.0

Emission
Factor
(grams/mi)
8.768
8.426
7.694
6.836
5.354
11.062
10.668
9.825
8.834
7.156
13.358
12.886
11.875
10.688
8.673
15.742
15.163
13.983
12.740
11.301
1.122
1.080
0.994
0.899
0.769
1.082
1.042
0.958
0.867
0.742
7.974
7.677
7.061
6.385
5.463
13.083
12.562
11.428
10.077
7.931

62

DVMT
(miles)
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486
506,030
9,572,593
10,851,158
5,295,330
2,257,486

Emissions
(lb/day)
5,914.2
107,511.5
111,284.5
48,247.2
16,111.6
2,174.2
39,663.0
41,406.6
18,168.8
6,274.8
1,282.8
23,409.5
24,454.8
10,740.9
3,715.6
668.0
12,172.0
12,724.0
5,657.2
2,139.3
2.5
45.6
47.6
21.0
7.7
16.9
308.2
321.2
141.8
51.8
658.9
12,000.9
12,512.3
5,521.4
2,014.0
73.0
1,326.8
1,368.3
588.8
197.6

Emissions
(kg/day)
2,682.7
48,767.2
50,478.7
21,884.9
7,308.2
986.2
17,991.2
18,782.0
8,241.3
2,846.2
581.9
10,618.5
11,092.7
4,872.1
1,685.4
303.0
5,521.2
5,771.6
2,566.1
970.4
1.1
20.7
21.6
9.5
3.5
7.7
139.8
145.7
64.3
23.5
298.9
5,443.6
5,675.6
2,504.5
913.5
33.1
601.9
620.7
267.1
89.6

Maricopa County, AZ

Table 5–4. CO Emissions by Vehicle Class, Area Type, and Facility Type (continued)

Facility
Type

Vehicle
Class

COLLECTOR

LDGV
with VMT
mix of
60.5%
LDGT1
with VMT
mix of
17.6%
LDGT2
with VMT
mix of
8.6%
HDGV
with VMT
mix of
3.8%
LDDV
with VMT
mix of
0.2%
LDDT
with VMT
mix of
1.4%
HDDV
with VMT
mix of
7.4%
MC
with VMT
mix of
0.5%

1999 CO Emissions Inventory

Area Speed
Type (mi/hr)
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7
1
24.0
2
24.3
3
25.6
4
28.1
5
27.7

Emission
Factor
(grams/mi)
9.963
9.830
9.292
8.393
8.526
12.427
12.277
11.662
10.630
10.784
14.997
14.816
14.077
12.840
13.024
17.851
17.612
16.652
15.108
15.331
1.271
1.255
1.187
1.076
1.093
1.226
1.210
1.145
1.038
1.054
9.034
8.915
8.435
7.649
7.763
14.843
14.651
13.864
12.511
12.715

63

DVMT
(miles)
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257
259,858
2,924,040
1,365,201
648,582
818,257

Emissions
(lb/day)
3,450.8
38,313.8
16,909.0
7,256.0
9,299.0
1,254.2
13,942.5
6,183.4
2,677.9
3,427.2
739.6
8,221.9
3,647.3
1,580.5
2,022.5
389.0
4,318.6
1,906.4
821.7
1,052.0
1.5
16.2
7.2
3.1
3.9
9.8
109.3
48.3
20.8
26.6
383.4
4,256.9
1,880.5
810.1
1,037.3
42.6
472.7
208.8
89.5
114.8

Emissions
(kg/day)
1,565.3
17,379.1
7,669.9
3,291.3
4,218.0
568.9
6,324.3
2,804.8
1,214.7
1,554.6
335.5
3,729.5
1,654.4
716.9
917.4
176.4
1,958.9
864.8
372.7
477.2
0.7
7.3
3.2
1.4
1.8
4.5
49.6
21.9
9.4
12.1
173.9
1,930.9
853.0
367.5
470.5
19.3
214.4
94.7
40.6
52.1

Maricopa County, AZ

Table 5–4. CO Emissions by Vehicle Class, Area Type, and Facility Type (continued)

Facility
Type

Vehicle
Class

LOCAL

LDGV
with VMT
mix of
60.5%
LDGT1
with VMT
mix of
17.6%
LDGT2
with VMT
mix of
8.6%
HDGV
with VMT
mix of
3.8%
LDDV
with VMT
mix of
0.2%
LDDT
with VMT
mix of
1.4%
HDDV
with VMT
mix of
7.4%
MC
with VMT
mix of
0.5%

1999 CO Emissions Inventory

Area Speed
Type (mi/hr)
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0
1
15.0
2
20.0
3
25.0
4
25.0
5
30.0

Emission
Factor
(grams/mi)
14.486
12.096
9.534
9.534
7.808
17.669
14.835
11.938
11.938
9.956
21.780
17.907
14.409
14.409
12.033
29.310
21.768
17.080
17.080
14.160
2.039
1.540
1.217
1.217
1.007
1.967
1.486
1.174
1.174
0.971
14.491
10.944
8.650
8.650
7.155
23.728
17.833
14.220
14.220
11.606

64

DVMT
(miles)
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453
59,240
1,811,216
2,176,263
1,080,974
172,453

Emissions
(lb/day)
1,143.8
29,201.9
27,654.5
13,736.3
1,794.8
406.5
10,435.9
10,090.5
5,012.1
666.9
244.9
6,155.5
5,951.4
2,956.1
393.8
145.6
3,306.2
3,117.1
1,548.3
204.8
0.5
12.3
11.7
5.8
0.8
3.6
83.2
78.9
39.2
5.2
140.2
3,237.0
3,074.1
1,526.9
201.5
15.5
356.4
341.5
169.6
22.1

Emissions
(kg/day)
518.8
13,246.0
12,544.1
6,230.8
814.1
184.4
4,733.7
4,577.0
2,273.5
302.5
111.1
2,792.1
2,699.5
1,340.9
178.6
66.0
1,499.7
1,413.9
702.3
92.9
0.2
5.6
5.3
2.6
0.3
1.6
37.7
35.8
17.8
2.3
63.6
1,468.3
1,394.4
692.6
91.4
7.0
161.7
154.9
76.9
10.0

Maricopa County, AZ

5.6

Summary of CO Emissions from Onroad Mobile Sources
Table 5-5 summarizes the calculated CO emissions by vehicle class, area, and facility type. Total CO

emissions from daily onroad mobile sources for the Maricopa County nonattainment area for the 1999 carbon
monoxide season are estimated to be 490,261 kilograms per day or 1,080,822 pounds per day.
NOTE: Consistent with the 1990 base year inventory, only seasonal emissions were calculated for this portion of the
inventory. In consultation with Mary Ann Warner-Selph, EPA Emissions Inventory Branch, it was determined that
annual emission estimates were unnecessary for the 1990 base year inventory.

5.7

Quality Assurance Process

5.7.1

VMT Estimates
Normal quality assurance (QA) procedures, including extensive automated consistency checks, were used

by ADOT in developing the 1999 HPMS data. A revised version of the 1999 data, incorporating improved traffic
count data, was submitted to the Federal Highway Administration in April 2001. Additionally, as recommended in
the Appendix B Level II Quality Review Checklist of the Quality Review Guidelines for 1990 Base Year Emission
Inventories, July 1992, VMT per gallon of gasoline consumed was calculated as a check of the VMT estimates as
described in Appendix 5-5.

5.7.2

Emission Factor Estimates
The QA process performed on the MOBILE5a analyses included accuracy, completeness, and

reasonableness checks. For accuracy and completeness, a system was used that included a two-layer, independent
reviewer set-up. All hard copy and computer-based data entries as well as all calculations procedures were checked
independently for accuracy and completeness by two different reviewers. Any errors found were corrected and the
changes were then rechecked by the reviewers.
The entire onroad mobile source portion of the 1999 periodic CO inventory was reviewed by MAG staff
that did not directly participate in its development. All comments were addressed.

5.7.3

Quality Review of 1999 Periodic CO Emission Inventory
The draft onroad mobile source portion of the 1999 periodic carbon monoxide inventory was reviewed

using published EPA quality review guidelines for base year emission inventories (EPA Document 450/4-91-022,
September 1991). The procedural review (Levels I, II, and III) included checks for completeness, consistency, and
the correct use of appropriate procedures.

1999 CO Emissions Inventory

65

Maricopa County, AZ

Table 5–5. Daily Onroad Mobile Source CO Emissions (in kg/day) by Vehicle Class,
Area Type and Facility Type – Winter
FACILITY
TYPE
INTERSTATE,
FREEWAY,
& EXPRESSWAY

LDGV
3,538.1
27,689.1
19,757.6
10,522.5
3,729.4
65,236.6

1
2
3
4
5
TOTAL

2,682.7
48,767.2
50,478.7
21,884.9
7,308.2
131,121.7

986.2
17,991.2
18,782.0
8,241.3
2,846.2
48,847.0

581.9
10,618.5
11,092.7
4,872.1
1,685.4
28,850.6

303.0
5,521.2
5,771.6
2,566.1
970.4
15,132.4

1
2
3
4
5
TOTAL

1,565.3
17,379.1
7,669.9
3,291.3
4,218.0
34,123.7

568.9
6,324.3
2,804.8
1,214.7
1,554.6
12,467.3

335.5
3,729.5
1,654.4
716.9
917.4
7,353.7

176.4
1,958.9
864.8
372.7
477.2
3,850.0

1
2
3
4
5
TOTAL

518.8
13,246.0
12,544.1
6,230.8
814.1
33,353.9
263,835.9

184.4
4,733.7
4,577.0
2,273.5
302.5
12,071.2
100,299.4

111.1
2,792.1
2,699.5
1,340.9
178.6
7,122.3
59,725.9

66.0
1,499.7
1,413.9
702.3
92.9
3,774.9
32,063.7

LDDV
1.9
13.0
9.1
3.8
1.2
29.0

LDDT
12.9
87.9
61.2
25.5
8.4
195.8

HDDV
501.4
3,421.8
2,384.5
991.8
326.2
7,625.7

MC
45.3
420.2
306.2
196.0
73.0
1,040.6

TOTAL
6,938.3
53,986.9
38,460.7
20,213.4
7,148.3
126,747.6

1
2
3
4
5
TOTAL

1.1
20.7
21.6
9.5
3.5
56.4

7.7
139.8
145.7
64.3
23.5
381.0

298.9
5,443.6
5,675.6
2,504.5
913.5
14,836.1

33.1
601.9
620.7
267.1
89.6
1,612.3

4,894.6
89,104.1
92,588.5
40,409.9
13,840.4
240,837.5

1
2
3
4
5
TOTAL

0.7
7.3
3.2
1.4
1.8
14.4

4.5
49.6
21.9
9.4
12.1
97.5

173.9
1,930.9
853.0
367.5
470.5
3,795.8

19.3
214.4
94.7
40.6
52.1
421.1

2,844.5
31,594.2
13,966.8
6,014.6
7,703.6
62,123.6

1
2
3
4
5
TOTAL

0.2
5.6
5.3
2.6
0.3
14.1
114.0

1.6
37.7
35.8
17.8
2.3
95.3
769.5

63.6
1,468.3
1,394.4
692.6
91.4
3,710.3
29,968.0

7.0
161.7
154.9
76.9
10.0
410.5
3,484.6

952.9
23,944.8
22,825.0
11,337.4
1,492.3
60,552.4
490,261.1

PRINCIPAL
ARTERIAL
&
MINOR
ARTERIAL

COLLECTOR

LOCAL

GRAND TOTAL
TYPE
INTERSTATE,
FREEWAY,
& EXPRESSWAY

VEHICLE CLASS
LDGT1
LDGT2
1,420.2
841.8
11,347.4
6,869.3
8,119.8
4,928.4
4,440.3
2,764.9
1,586.3
995.0
26,914.0
16,399.4

AREA TYPE
1
2
3
4
5
TOTAL

AREA TYPE
1
2
3
4
5
TOTAL

PRINCIPAL
ARTERIAL
&
MINOR
ARTERIAL

COLLECTOR

LOCAL

GRAND TOTAL

1999 CO Emissions Inventory

66

HDGV
576.7
4,138.3
2,894.0
1,268.7
428.8
9,306.4

Maricopa County, AZ

Additionally, the draft onroad mobile source portion of the 1999 periodic carbon monoxide inventory was
compared with the onroad mobile source portions of the 1990, 1993, and 1996 base year and periodic inventories.
The results are in the following table.

Year of
Analysis
1990

Onroad Emissions
(kg/season day)
732,745

Onroad Emissions
(pounds/season day)
1,615,399

Vehicle Miles
Traveled
(VMT/season day)
45,877,773

1993

553,943

1,221,215

48,153,240

1996

508,259

1,120,500

53,091,273

1999

490,261

1,080,822

57,853,980

While the VMT increases over time, the modeled onroad CO emissions continue to decrease, principally
because of a vehicle fleet with cleaner engine and emission control technologies, augmented by local controls such
as the I/M program and cleaner gasoline. It is important to note that the base case emissions from the Serious Area
CO Plan may not match those in the periodic inventories because of a different year modeled and different modeling
domain size.

5.8

References for Section 5

Emission Inventory Requirements for Carbon Monoxide State Implementation Plans, EPA-450/4-91-011,
March 1991.
MAG 1999 Serious Area Carbon Monoxide Plan for the Maricopa County Nonattainment Area, MAG,
June 1999.
Maricopa Association of Governments Highway Performance Monitoring System Update, Lee
Engineering, Inc., for MAG, January 1995.
1986 Phoenix Urbanized Area Travel Speed Study, Parsons Brinkerhoff Quade & Douglas, Inc., for MAG,
October 1986.
1993 Study of Travel Speed and Delay in the MAG Region, Lee Engineering, Inc., for MAG, January
1995.
Procedures for Emission Inventory Preparation Volume IV: Mobile Sources, EPA-450/4-81-026d
(Revised), 1992.
Quality Review Guidelines for 1990 Base Year Emission Inventories, EPA-454/R-92-007, July 1992.
User's Guide to MOBILE5 (Mobile Source Emission Factor Model), EPA-AA-AQAB-94-01, May 1994.

1999 CO Emissions Inventory

67

Maricopa County, AZ

SECTION 6. QUALITY ASSURANCE
6.1

Introduction
This section describes the Quality Assurance (QA) procedures followed by the Maricopa County

Environmental Services Department (MCESD) in the production of this 1999 periodic carbon monoxide emissions
inventory for the Maricopa County nonattainment area. This section does not include the QA procedures taken
when preparing the onroad mobile section of this inventory which are described in Section 5.7. When preparing
stationary point, stationary area, and the aircraft and locomotive section of nonroad mobile sources these procedures
were followed:
1. Reviewing the descriptive information included in each section to assure completeness, clarity and
correctness;
2. Inspecting formulas, calculations and conversions to assure autonomy from errors and inconsistencies;
3. Evaluating data quality to assure the value of the inventory, both as a representative data set of the state of
the air environment in the Maricopa County nonattainment area and as the reference point for future
inventories; and
4. Assessing, where possible, the significance of the calculated quantities to assure reasonable accuracy and
admissible precision.
The QA section of the Maricopa County emissions inventory follows the QA/QC plan in the Inventory
Preparation Plan for the 1999 Periodic CO Emission Inventory (MCESD, 2001). This should show, without
ambiguity, that Maricopa County's QA plan was implemented.

6.2

Purpose of an Emissions Inventory
Several objectives motivated the development of the emissions inventory:
1. To comply with the inventory requirements of the Federal Clean Air Act Amendments of 1990 and
specifications of the U.S. Environmental Protection Agency;
2. To provide a baseline against which to evaluate trends and successes in CO emission reduction efforts;
3. To support development of air quality models and planning activities; and,
4. To underscore particular concerns and to direct attention to areas where significant air quality
improvement is achievable.
To assure production of an emissions inventory that is complete, accurate, and in compliance with

requirements set forth in the EPA document Guidance for the Preparation of Quality Assurance Plans for Ozone /
Carbon Monoxide SIP Emission Inventories, four operational steps were followed: 1) planning; (2) collecting data,
distinguishing point sources from area sources and establishing data collection procedures appropriate for each type
of source considered; (3) analyzing data and developing emission estimates for each type of source; and (4)
summarizing and reporting data.

1999 CO Emissions Inventory

68

Maricopa County, AZ

6.3

Quality Assurance Staff
The Quality Assurance program staff is comprised of:

6.4

Renee Kongshaug, MCESD

Internal QA Coordinator

Bob Downing, MCESD

Point sources

Ruey-in Chiou, MAG

Highway vehicle emissions

Randy Sedlacek, ADEQ

Oversight and external QA

Implementation
Quality assurance checks occurred on receipt of data (missing and/or questionable data), on completion of

calculations (computational methods, accuracy, reasonableness), on formatting of data (transcription errors,
reasonableness either on a facility or categorical basis), and on inventory assembly (completeness, reasonableness).
The QA point and area source coordinator reviewed the Inventory Preparation Plan (IPP) (MCESD, 2001), checked
calculations, identified errors, performed completeness, reasonableness and accuracy checks.
Data collection procedures followed EPA guidance to assure inclusion of all source categories in the
inventory. A listing of point sources was assembled from the existing point source inventory and the county’s
inventory database, EMS (described in Section 2). Any questionable data were verified by telephone, fax or e-mail.
Examples of data collection and data verification procedures are included in Appendix 2–1.
Data quality was evaluated using several approaches. Data were cross-checked where multiple sources
were available, and activity-level based data were given preference. All calculations were reviewed for accuracy
and method consistency, and those calculations done in spreadsheets were recalculated with a calculator or by hand
as an error checking procedure. Examples of these recalculations are included in Appendix 2–1.
MCESD made necessary corrections to the inventory as errors were revealed through its own QA
procedures and as recommended by other agencies. As a final check before the inventory was considered complete,
MCESD staff completed the electronic inventory review checklists (see Appendix 6–1). These checklists cover
Level I and Level II checks (EPA, August 1992). During this final review, staff discovered only minor areas that
needed attention. Data handling and reporting essentially is a reflection of EPA guidance documents and data
reporting requirements. External comments made while reviewing the draft document are included in Appendix 6-2.
6.5

Review and Evaluation of Inventory Elements

6.5.1

General Statement
The general plan of the quality assurance program is described in the IPP (MCESD, 2001). Formal training

sessions for inventory personnel were provided by EPA training workshops, as available. Informal training sessions
for MCESD inventory staff were held as further EPA guidance became available. Topics covered in these sessions
included:

1999 CO Emissions Inventory

69

Maricopa County, AZ

1.

Contents of existing and new EPA emissions inventory-related guidance or policy.

2.

New or updated data sources or procedures for determining emissions estimates.

3.

National Emission Inventory/ NIF training.

4.

MCESD policy and standard operating procedures.
New personnel received briefings from their respective supervisors. However, most of their training

regarding the details of their duties was received while on the job. Training materials (e.g., books and manuals)
were available to familiarize new personnel with inventory work.

6.5.2

Point Sources
Two environmental planners checked inventory accuracy, reasonableness and assured that all point sources

had been identified and that the methodology applied to calculate emissions was appropriate and that the
calculations were correct. Other reasonableness checks were conducted by recalculating emissions by using
methods other than those used to make the initial emissions calculations and then by comparing results. A quality
assurance check of EMS was made on all SCC codes for determining the appropriate categories for facility’s
emission units. Quality analysis (QA) was conducted by checking all emissions reports submitted to MCESD for
the year 1999 for missing and questionable data and by checking the accuracy and reasonableness of all emissions
calculations made for such reports. Notes concerning follow-up calls and corrections to calculations were
documented on each 1999 annual emissions report.
Data entry for the NEI will be verified against the original hardcopy files for completeness and
reasonableness. Since some data sources are more reliable than others, it is important that the reliability of the data
be taken into account. For this reason, MCESD assessed all data against the capabilities and biases (if any, and if
known) of the organization supplying the data, the techniques used to collect the data (if known), and the purpose
for which the data were compiled. This assessment allowed MCESD to understand the limitation of the data and to
choose the best data for developing emissions estimates.
Inconsistencies were located in the data presentation (i.e. significant figures) and were corrected. General
corrections to format were made including references to specific appendices. Text was added to clarify how peak
CO season daily emissions were calculated. There had been some facility name discrepancies that were corrected.
Text was added to clarify that the power plant peak CO season daily emission estimates came from data provided by
each source for a worst case day in 1999. Text was also added to clarify that all point sources were re-inventoried
and to outline the criteria for a facility to be included as a point source.

1999 CO Emissions Inventory

70

Maricopa County, AZ

6.5.3

Area Sources

In the creation of the area source emissions inventory, two environmental planners checked data and calculations for
accuracy, completeness and reasonableness and then reviewed the methodology, and rechecked data for
completeness, reasonableness, and a sample of the calculations. All miscalculations were corrected and then
rechecked. All issues were discussed. A number of format changes were made along with adding more text, a new
category and some changes in methodology.
The external reviewer checked accuracy in methodology based on the Procedures for the Preparation of Emission
Inventories for Carbon Monoxide and Precursors of Ozone, Volume I (EPA, May, 1991) document. It was verified
that all source categories listed in the Emission Inventory Requirements for Carbon Monoxide State Implementation
Plans (EPA, March 1991) document were included. Reasonableness checks were performed by recalculating
emissions using alternate methodologies and by comparing results and/or analyzing totals and inputs to determine
reasonableness.
Significant figures inconsistencies were located in the data presentation and were corrected. Example calculations
were added to each section for clarity. Conversations with the natural gas suppliers led to corrections to the
document and calculations. General corrections to format were made including references to specific appendices.
Stationary Area Sources - Fuel Combustion
Input data in this source category are of high quality and verifiable by independent calculation. Within
Maricopa County, natural gas is the principal fuel burned. Quantities of natural gas distributed to sub-categories
(e.g. Electric Utilities, Industrial, etc.) were obtained from three distribution sources and were subtracted from point
source usage (data obtained from EMS, Maricopa County’s database) to estimate area source usage. These
calculations were rechecked and a few errors from inconsistent emission factors or coding discrepancies were
corrected.
Stationary Area Sources - Other Combustion
This category combined several miscellaneous sources, many with roughly estimated emission factors.
Qualitative dimensional assumptions and gross estimates of the quantities of materials burned were made. However,
these reported quantities are so large, and their calculated contributions to the CO emission inventory of area sources
are so significant, that they may overwhelm the more substantiated emission values of other sources.
This is especially true in the case of wood burning in fireplaces and woodstoves. This sub-category
accounts for 87% of the reported 1999 CO emissions contributed by "Other Combustion" sources (2,830.2 tons/year
of a total 3,241.2 tons/year), yet the reported emission level is based on questionable assumptions of fireplace
population and of the extent of the wood burning season.

1999 CO Emissions Inventory

71

Maricopa County, AZ

Similar reservations exist for the sub-category "Structure and Motor Vehicle Fires"; however, the total
reported emissions of this group are a much less significant contribution to the inventory.

6.5.4

Nonroad Mobile Sources
The quality assurance process for 1999 aircraft and locomotive CO emissions engaged the efforts of two

environmental planners validating input data and performing calculations and reasonableness checks on each other's
work. This was followed by an external reviewer's check of the section. The QA coordinator checked for accuracy,
reasonableness, completeness of emission sources and logical methodology based on chapters five and six of the
EPA Emission Inventory Preparation Document (EPA, 1992). Several formatting inconsistencies were found and
corrected. Additional reference material was requisite to document sources of information, and therefore included.
An error in aircraft operations was discovered, and the correction created a series of amendments to the document
and calculations. All issues were addressed and corrected.
General corrections to format were made including references to specific appendices. References were
added to indicate the source of aircraft activity information for each airport.

6.5.5

Onroad Mobile Sources
See Section 5.7 of this document for the quality assurance narrative regarding this category.

6.6

Summary Statement
The accuracy of this inventory is a measure of the quality of our knowledge of the day-to-day, seasonal and

annual statistics of emissions sources in the Maricopa County nonattainment area. Although effort was made to
ensure that the data expressed in this inventory accurately represents the emissions in the nonattainment area in
1999, all components of the inventory, taken together, are subject to continued improvement.
The degree to which we are able to improve the quantity and accuracy of source data will determine the
quality and reliability of future inventories. Efforts will be focused on obtaining valid and reliable information as
well as improving emission calculation methods for future inventories.

1999 CO Emissions Inventory

72

Maricopa County, AZ

6.7

References for Section 6

Maricopa County Environmental Services Department. Inventory Preparation Plan: Carbon Monoxide.
April 2001.
U. S. Environmental Protection Agency. Procedures for the Preparation of Emission Inventories for
Carbon Monoxide and Precursors of Ozone, Vol. I. EPA-450/4-91-016. May 1991.
U. S. Environmental Protection Agency. Emission Inventory Requirements for Carbon Monoxide State
Implementation Plans. EPA-450/4-91-011. March 1991.
U. S. Environmental Protection Agency. Procedures for Emission Inventory Preparation, Volume IV:
Mobile Sources. EPA-450/4-81-026d (Revised), Chapter 5. Office of Mobile Sources. Ann Arbor, MI. 1992.
U.S. Environmental Protection Agency. Procedures for Emission Inventory Preparation, Volume IV:
Mobile Sources. EPA-450/4-81-026d (Revised), Chapter 6. Office of Mobile Sources, Ann Arbor, MI. 1992.
U. S. Environmental Protection Agency. Procedures for the Preparation of Emission Inventories for
Carbon Monoxide and Precursors of Ozone, Vol. III: Emission Inventory Requirements for Photochemical Air
Quality Simulation Models, EPA-450/4-91-014. May, 1991.
U. S. Environmental Protection Agency. Guidance for the Preparation of Quality Assurance Plans for
Ozone/Carbon Monoxide SIP Emission Inventories. EPA-450/4-88-023.
U. S. Environmental Protection Agency. Quality Review Guidelines for 1990 Base Year Emissions
Inventories, EPA-450/4-91-022. August 1992.
U.S. Environmental Protection Agency. EIIP Volume VI: Chapter 3 General QA/QC Methods, June 1997.

1999 CO Emissions Inventory

73

Maricopa County, AZ