Pinal County, Arizona 

Area Designation for the 2006 24-hour Fine Particle 

National Ambient Air Quality Standard 

Technical Support Document 

May 5, 2010 

US Environmental Protection Agency 

Region 9 
Table of Contents 

Introduction ...................................................................................................................................... 1

Factor 1: Emissions Data .................................................................................................................... 5 

Factor 2: Air Quality Data ................................................................................................................ 15

Factor 3: Population Density and Degree of Urbanization ................................................................. 18

Factor 4: Traffic and Commuting Patterns ........................................................................................ 21

Factor 5: Growth Rates and Patterns ............................................................................................... 22

Factor 6: Meteorology ..................................................................................................................... 24

Factor 7: Geography and Topography .............................................................................................. 30

Factor 8: Jurisdictional Boundaries .................................................................................................. 33

Factor 9: Level of Control of Emissions Sources ............................................................................... 35

Appendix A – Emissions in Pinal County: Primary PM2.5, NOx, NH3, SO2, VOCs ................................... A-1

Appendix B – Meteorological Data ................................................................................................. B-1
1 

PINAL COUNTY, ARIZONA

AREA DESIGNATION FOR THE 2006 24-HOUR FINE PARTICLE NAAQS 

EPA intends to designate a portion of Pinal County as not attaining the 2006 24-hour PM2.5 

national ambient air quality standards (NAAQS).1 A county or portion of a county will be 

designated as nonattainment if it has an air quality monitor that is violating the standard or if the 

county or portion of a county is determined to be contributing to the violation of the standard. 

EPA intends to designate the remainder of Pinal County, Cochise, Gila, Graham, La Paz, 

Maricopa, Pima, Yavapai, and Yuma counties, and, as noted below, Indian country2

 located 

within those areas, as “unclassifiable/attainment.” EPA is deferring designation of the Gila River 

Indian Community and Ak-Chin Indian Community reservations, which are located in this 

portion of Pinal County. 

EPA Technical Analysis for Pinal County 

Introduction 

Pursuant to section 107(d) of the Clean Air Act, EPA must designate as nonattainment those 

areas that violate the national ambient air quality standards (NAAQS) and those nearby areas that 

contribute to the violations. This technical analysis identifies the monitor that violates the 24-

hour PM2.5 standard and evaluates surrounding counties for contributions to fine particle 

concentrations in the area. EPA has evaluated these counties based on the weight of evidence of 

the following nine factors recommended in EPA guidance and any other relevant information: 

- pollutant emissions 

- air quality data 

- population density and degree of urbanization 

- traffic and commuting patterns 

- growth 

 

1

EPA designated nonattainment areas for the 1997 fine particle standards in 2005. In 2006, the 24-hour PM2.5 

standard was revised from 65 micrograms per cubic meter (average of 98th percentile values for 3 consecutive 

years) to 35 micrograms per cubic meter; the level of the 1997 annual standard for PM2.5 remained unchanged at 15 

micrograms per cubic meter (average of annual averages for 3 consecutive years). 

2

 “Indian country” as defined at 18 U.S.C. 1151 refers to: “(a) all land within the limits of any Indian reservation 

under the jurisdiction of the United States Government, notwithstanding the issuance of any patent, and, including 

rights-of-way running through the reservation, (b) all dependent Indian communities within the borders of the 

United States whether within the original or subsequently acquired territory thereof, and whether within or without 

the limits of a state, and (c) all Indian allotments, the Indian titles to which have not been extinguished, including 

rights-of-way running through the same.” The lands of the Fort McDowell Yavapai, Salt River Pima-Maricopa, San 

Carlos Apache and Tohono O’odham tribes will be designated “unclassifiable/attainment.” 
2 

- meteorology 

- geography and topography 

- jurisdictional boundaries 

- level of control of emissions sources 

We also used analytical tools and data such as pollution roses, coarse particle composition 

monitoring data, and the correlation between meteorological data and composition data to 

evaluate these areas. 

Figure 1 is a map of the counties in the area and other relevant information such as the locations 

of air quality monitors. Pinal County and Maricopa County comprise the Phoenix-MesaScottsdale Core-Based Statistical Area (CBSA). 

Figure 1. PM2.5 Monitors – Pinal County and Surrounding Counties 

In response to EPA’s promulgation of the revised 24-hour PM2.5 NAAQS in 2006, the Governor 

of Arizona, by letter dated December 19, 2007, recommended that all portions of the state, with 

the exception of the Nogales area, be designated as “attainment” for the 2006 24-hour PM2.5

standard based on air quality data from 2004-2006. These data are from Federal Reference 
3 

Method (FRM) monitors located in the state. The State of Arizona does not have jurisdiction 

over Indian country. 

In October of 2009, EPA notified the Governor of Arizona and Tribal leaders of tribes with lands 

located in Pinal and Maricopa counties that a monitor in Pinal County was violating the 24-hour 

PM2.5 standard based on the most recent (2006-2008) air quality monitoring data. Due to this 

new violation, and due to the need for additional time to collect data and evaluate the area to 

determine an appropriate nonattainment area boundary, EPA decided to defer the area 

designation of Pinal County, Maricopa County (i.e., the other county comprising the PhoenixMesa-Scottsdale CBSA), and the seven counties (i.e., Cochise, Gila, Graham, La Paz, Pima, 

Yavapai, and Yuma Counties) surrounding the Phoenix-Mesa-Scottsdale CBSA, for the 2006 24-

hour PM2.5 standard.3 

Based on EPA’s technical analysis, EPA believes the central-western portion of Pinal County, 

Arizona, should be designated as “nonattainment” for the 24-hour PM2.5 NAAQS as shown in 

Figure 2. Emission inventory data, combined with speciation and source apportionment data, 

point to agricultural activities and cattle feedlots, as well as other nearby sources of PM2.5, as 

primary sources contributing to PM2.5 levels at the Cowtown monitor on days with exceedances 

of the 24-hour PM2.5 NAAQS. In addition, EPA assessed air quality and meteorological data, 

including data on monthly exceedances of the 24-hour PM2.5 standards; wind direction and speed 

for hourly and daily PM2.5 levels; correlation of PM2.5 with PM10 at the Cowtown monitoring 

site; and, the diurnal pattern of PM10, wind speed, and temperature for PM2.5 exceedance days. 

Results of these assessments indicate that agricultural lands and cattle feedlots, and activities 

associated with these operations, particularly those to the south and southwest of the monitor, are 

contributing to PM2.5 levels at the monitoring site. 

 

3

 Unless otherwise specified, references to “counties” or to “Arizona” include all lands within the geographic 

boundary and do not differentiate between lands under state or tribal jurisdiction. 
4 

Figure 2. EPA Proposed Nonattainment Area Boundary

Except as noted below, EPA intends to designate the remaining portion of Pinal County, 

including those lands of the Tohono O’odham Nation, and the San Carlos Apache Tribe that are 

located in Pinal County, Arizona, as “unclassifiable/attainment” for the 2006 24-hour PM2.5

NAAQS. 

The population density on the lands of the Tohono O’odham Nation, which lie to the south and 

west of EPA’s intended nonattainment area is very low at approximately 3 people per square 

mile, and the types of sources that data indicate are the primary contributors to exceedances of 

the 24-hour PM2.5 NAAQS in Pinal County (e.g., cattle feedlots and unpaved roads) either are 

not present on Tohono O’odham tribal lands or are present in small amounts. EPA has therefore 

concluded that any emissions activities occurring there are not contributing to nonattainment at 

the violating monitor in Pinal County. 

The lands of the San Carlos Apache Tribe are located at a considerable distance from the 

proposed nonattainment area and are separated from it by mountainous terrain. Therefore, EPA 

concludes that any emissions activity there is not contributing to the violation at the monitor in 

Pinal County. Accordingly, EPA intends to designate the lands of the San Carlos Apache Tribe 

as “unclassifiable/attainment.” 
5 

EPA is deferring designation of the lands of the Ak-Chin Indian Community and the Gila River 

Indian Community4

 in order to consider unique issues involving these tribal lands and to 

complete formal consultation with these tribal governments. 

EPA intends to designate the eight counties surrounding Pinal County, including Indian country 

that lies within those counties, as “unclassifiable/attainment” for the 24-hour PM2.5 NAAQS. 

These counties are: Cochise County, Gila County, Graham County, La Paz County, Maricopa 

County, Pima County, Yavapai County, and Yuma County. As stated above and described in 

more detail below, there are no violating monitors in these counties, and evaluation of the nine 

factors supports a finding that emissions within the eight subject counties do not contribute to the 

PM2.5 violations recorded at the Cowtown monitor for the purposes of section 107(d) of the 

Clean Air Act. With respect to Cochise, Gila, Graham, and Yavapai counties, this conclusion is 

supported by, among other factors, the speciation and source apportionment data for the 

Cowtown monitor (which point to the predominance of local sources), the distance between 

sources in these counties and the proposed nonattainment area, the presence of topographical 

features inhibiting emissions transport to the Cowtown monitor location, and the low direct 

PM2.5 emissions and population densities characteristic of these counties. For La Paz and Yuma 

counties, topography plays a lesser role, but the other factors, the speciation and source 

apportionment data for the Cowtown monitor (which point to the predominance of local 

sources), the distance between sources in these counties and the proposed nonattainment area, as 

well as the low direct PM2.5 emissions and population densities characteristic of these counties, 

support a finding of little or no contribution from La Paz and Yuma counties. 

For Maricopa County, the closest county with significant population, the meteorological 

evaluation along with the speciation and source apportionment data lends support to a finding of 

little or no contribution. For Pima County, the finding of little or no contribution relies upon the 

speciation and source apportionment data, the correlation between PM2.5 and PM10

concentrations, and the review of contemporaneous ambient concentration, wind speed and wind 

direction data at the Cowtown monitor during periods when exceedances have been recorded. 

The following is a summary of EPA’s technical analysis, which supports the boundaries of the 

nonattainment designation for the Pinal County 2006 24-hour PM2.5 nonattainment area and the 

attainment/unclassifiable designation for the remainder of Pinal County, Cochise, Gila, Graham, 

La Paz, Maricopa, Pima, Yavapai, and Yuma counties, and, except as noted above, Indian 

country located within those areas. 

Factor 1: Emissions data 

For this factor, EPA evaluated county-level emission data for the following PM2.5 components 

and precursor pollutants: “Primary PM2.5,” “SO2,” “NOx,” “VOCs,” and “NH3.” “Primary 

PM2.5” represents direct emissions of PM2.5 and includes: “PM2.5 emissions carbon,” “PM2.5

emissions other,” primary sulfate (SO4), and primary nitrate. (Although primary sulfate and 

primary nitrate, which are emitted directly from stacks rather than forming in atmospheric 

reactions with SO2 and NOx, are part of “PM2.5 emissions total,” they are not shown in Table 1 as

 

4

 Gila River Indian Community reservation straddles the border between Pinal and Maricopa counties. Designation 

for the entire reservation, including the portion located within Maricopa County, is deferred. 
6 

separate items.) “PM2.5 emissions carbon” represents the sum of organic carbon (OC) and 

elemental carbon (EC) emissions, and “PM2.5 emissions other” represents other inorganic 

particles (crustal). Emissions of SO2 and NOx, which are precursors of the secondary PM2.5

components sulfate and nitrate, are also considered. VOCs (volatile organic compounds) and 

NH3 (ammonia) are also potential PM2.5 precursors and are included for consideration. 

Table 1 shows emissions of PM2.5 and precursor pollutants (given in tons per year) for counties 

with violating monitors and potentially contributing counties surrounding Pinal County. The 

emissions data were derived from the most current version of the national emissions inventory, 

the 2005 National Emissions Inventory, version 2 (NEIv2).5 

Table 1. Emission Totals Per County (tons per year). 2005 NEI version 2. 

County 

Primary 

PM2.5 

Emissions NOx NH3 SO2 VOC 

Pinal 4,210 12,545 5,646 757 9,217 

Maricopa 14,836 99,947 19,318 5,276 108,548 

Cochise 2,939 16,137 3,531 3,826 8,838 

Gila 2,316 2,098 553 20,342 7,592 

Graham 903 1,010 494 61 1,894 

La Paz 573 3,017 597 148 2,604 

Pima 4,827 30,412 1,878 6,157 31,169 

Yavapai 4,717 14,640 1,300 1,912 11,552 

Yuma 1,748 9,219 4,370 555 7,138 

While many of the surrounding counties generate substantial emissions of primary PM2.5 and 

PM2.5 precursors relative to Pinal County, as explained further below, the composition of the 

particles measured at the Cowtown monitor on high PM2.5 days, combined with meteorological 

data and the presence of topographic barriers, indicate that there is a negligible contribution from 

the surrounding counties to the total PM2.5 levels at the violating monitor. 

 

5

http://www.epa.gov/ttn/chief/net/2005inventory.html#inventorydata. Retrieved February 3, 2010. 
7 

To determine what nearby sources exist, EPA considered additional emissions data for the 

county containing the violating monitor. Table 2 lists source categories in Pinal County that emit 

direct (primary) PM2.5 according to the 2005 NEIv2. Open burning, agriculture (including crop 

tilling and livestock dust), unpaved roads and construction account for 67% of the primary PM2.5 

emissions in Pinal County. Additional tables showing source categories in Pinal County that 

emit nitrogen oxides, ammonia, sulfur dioxide, and volatile organic compound emissions may be 

found in Appendix A. 

Table 2. Primary PM2.5 Sources in Pinal County* (includes filterables + condensables**). 

2005 NEI version2. 

Source Category 

Emissions 

(tpy) 

% of Total Primary 

PM2.5 Emissions, 

Pinal County 

Nonpoint 

 Waste Disposal - Open Burning 886 21% 

 Agriculture - Crop Tilling & Livestock Dust 751 18% 

 Unpaved Roads 626 15% 

 Construction 547 13% 

 Wildfires 395 9% 

 Industrial Process – not elsewhere classified 220 5% 

 Paved Roads 152 4% 

 Other Nonpoint 105 2% 

Nonroad 

 Non-Road Equipment – Diesel 166 4% 

 Planes, Trains, & Ships 64 2% 

 Non-Road Equipment – Gasoline 38 1% 

Onroad 

 On-Road Vehicles – Diesel 116 3% 

 On-Road Vehicles – Gasoline 42 1% 

Point 

 Misc. Point 102 2% 

TOTAL: 4,210 100%

*Emissions from tribal lands are not included because tribes are not required to submit 

information to the NEI. 

** Filterable PM consists of particles that are directly emitted as a solid or liquid at stack or 

release conditions and are captured on the filter of a stack test train. Condensable PM is material 

that is in the vapor phase at stack conditions but condenses and/or reacts upon cooling and 

dilution in the ambient air to form a solid or a liquid particulate immediately after discharge 

from the stack. 

Sources in the immediate vicinity of the Cowtown monitor include cattle feedlots, an ethanol 

plant, agricultural fields, and a commercial composting facility. The monitor is approximately 

300 yards from the closest feedlot. Four different cattle operations (Sawyer Cattle Company, 

OK Cattle Co., Maricopa Feedyard LLC, and Pinal Feeding Co.) are located immediately 
8 

northwest, west, south, and southeast of the monitor and account for approximately 424 acres of 

feedlot.6

 As shown by Figure 3, active and fallow agricultural fields surround the area. Figure 4 

shows issued construction permits, and point sources emitting direct PM2.5 near the Cowtown 

monitor. Also shown is a close-up of the Cowtown monitor and surrounding operations. Figure 

5 shows paved and unpaved roads within fifty miles of the Cowtown monitor. 

Figures 3, 4, and 5 reflect information for both tribal and non-tribal lands. Figure 3 contains 

agriculture information from the USDA (2006), and feedlot, dairy and additional cattle 

operations information from the Dun and Bradstreet business database (2007) and Google Earth 

(retrieved February 3, 2010). Figure 4 shows construction permits issued according to ADEQ 

(2010) and point sources from EPA’s 2005 NEI version 2. Figure 5’s paved and unpaved roads 

information originates from Teledyne Atlas of North America (2006) and U.S. Department of 

Commerce, U.S. Census Bureau, Geography Division (2008), respectively. 

 

6

 Dun & Bradstreet Agricultural Data 
9 

Figure 3. Agriculture, Feedlots, Dairies, and Additional Cattle Operations.7

7 USDA 2006; Dun and Bradstreet business database 2007; Google Earth February 3, 2010. 
10 

Figure 4. Construction and Point Sources within Fifty Miles of the Cowtown PM2.5 Monitor.8

8 ADEQ 2010; 2005 NEI version 2. 
11 

Figure 5. Paved and Unpaved Roads within Fifty Miles of the Cowtown PM2.5 Monitor.9

9 Teledyne Atlas of North America 2006; U.S. Department of Commerce, U.S. Census Bureau, Geography Division 2008. 
12 

In 2003, Pinal County Air Quality Control District (PCAQCD) undertook a source 

apportionment study to determine what sources were contributing to elevated PM levels.10

 

Chemical fingerprints were developed for feedlot soil emissions, agricultural soil emissions, and 

dirt road soil emissions. The feedlot emissions contained a substantial amount of total carbon 

(particularly OC3), making it a distinguishable signature. The chemical analysis was not able to 

distinguish between agricultural and dirt road emissions. The report notes that a high total 

carbon signature may not only be associated with feedlots, but possibly with agricultural fields 

recently covered with manure. The report does not mention the composting facility near the 

Cowtown monitor; however, emissions from this source could also show high total carbon. 

Open burning, agricultural fields, livestock, unpaved roads and construction are the source 

categories with the highest direct PM2.5 emissions in Pinal County according to the 2005 NEIv2. 

One would expect significant geological soil and feedlot/manure signatures from the majority of 

these source types, which is consistent with the Pinal County source apportionment study 

findings. 

As shown in Figure 6, 24-hour PM2.5 data collected at Cowtown in October and November 2003 

showed an average contribution of 49% from the feedlot soil category and 24% from geological 

soil. The average concentration was 67 micrograms per cubic meter (μg/m3), with three samples 

over 100μg/m3

. Each of these three sample days showed inversion conditions with light winds 

throughout the day. 

Figure 6. PM2.5 Cowtown Monitor Average Source Contributions.11

Soil Geological soil ColPP Coal fired power plant 

Feedlot Feedlot soil AmSulf Ammonium sulfate 

MV Emi Motor vehicle 

combustion emissions 

 AmNitr Ammonium nitrate 

VgBr Vegetative burning Other Unclassified sources

 

 

10 Pinal County Air Quality Control District Source Apportionment Study: July 29, 2005 

11 Pinal County Air Quality Control District Source Apportionment Study: July 29, 2005, p 35. 
13 

Figure 7 (Table 9 and Figure 7 from the Pinal County Source Apportionment Study) illustrates 

the correlation between higher levels of PM2.5 and increased levels of feedlot and soil emissions. 

The feedlot contribution ranged from 1.41 μg/m3 on October 12, 2003, when the total measured 

PM2.5 was 15.7 μg/m3

 (9% of the total), to 146.29 μg/m3 on October 27, 2003, when the total 

measured PM2.5 was 183.38 ug/m3 (79.8% of the total). The soil component also varied 

significantly, with the highest measured levels occurring on days when the overall PM2.5 levels 

were highest. On days when measured PM2.5 levels were at or above 35 μg/m3, the combined 

feedlot and soil emissions contribution to total PM2.5 mass ranged from 68% to 96% of the total. 

In contrast, the contribution of other sources (e.g., vegetation burning and coal-fired power plant) 

was relatively constant and low. For example, for days that data were collected, the contribution 

from coal-fired power plants ranged from 1.73 to 5.05 μg/m3

 and averaged 3.53 μg/m3. 
14 

Figure 7. PM2.5 Source Attributions from Pinal County Source Apportionment Study 
15 

The Pinal County source apportionment study results indicate that violations of the 2006 24-hour 

PM2.5 NAAQS in Pinal County may be the result of contribution from significant local, rather 

than regional, sources of emissions of PM2.5. For example, the high proportion of directly 

emitted particles suggests that there is little contribution from more distant sources of PM2.5 

precursor emissions in surrounding counties. Unlike other areas, where the monitored PM2.5

does not have such characteristics, and instead reflects both regional and local contribution, the 

analysis of this area indicates that certain source categories in the surrounding area are those that 

contribute sufficiently to require inclusion within the designated nonattainment area. 

The following sections of this TSD further discuss how other factors, including air quality data 

and meteorology, indicate that nearby direct PM2.5 emission sources are responsible for the 

majority of the monitored PM2.5 levels at the Cowtown monitoring site. 

Factor 2: Air Quality Data 

This factor considers the 24-hour PM2.5 design values (in μg/m3) for air quality monitors in Pinal 

County and the surrounding counties based on data for the 2006-2008 period. A monitor’s 

design value indicates whether that monitor attains a specified air quality standard. The 24-hour 

PM2.5 standards are met when the 3-year average of a monitor’s 98th percentile values are 

35μg/m3

 or less. A design value is only valid if minimum data completeness criteria are met. 

The location of PM2.5 monitors and design values for these monitors are shown in Figure 8. 

Eligible monitors for providing design value data generally include state and local air monitoring 

stations (SLAMS) at population-oriented locations with a federal reference method (FRM) 

monitor. All data from special purpose monitors (SPM) using an FRM is eligible for comparison 

to the relevant NAAQS, subject to the requirements given in the October 17, 2006 Revision to 

Ambient Air Monitoring Regulations (71 FR 61236). All monitors used to provide data must 

meet the monitor siting and eligibility requirements given in 71 FR 61236 to 61328 in order to be 

acceptable for comparison to the 24-hour PM2.5 NAAQS for designation purposes. 

The 24-hour PM2.5 design values for the individual monitors in Pinal County are shown in Table 

3. Table 4 lists the design value for surrounding counties (based on the highest reading monitor). 

Table 3. PM2.5 Pinal County Air Quality Monitoring Data 

Site Name AQS ID PM2.5 24-hour Design Value 

2006-2008 

Casa Grande 04-021-0001-1 20 μg/m3

Apache Junction 04-021-3002-1 13 μg/m3

Cowtown 04-021-3013-1 48 μg/m3

EPA notes that the monitor located at Cowtown shows ambient levels more than twice as high as 

those of the other monitors located in Pinal. This suggests that there may be sources that 

contribute more to that monitor than to the others, and that the sources may be in the vicinity of 

the violating monitor. 
16 

The Cowtown monitor is located near a number of cattle feedlots. A grain processing facility and 

a commercial composting facility are also located nearby. This source mix mostly likely 

represents a relatively unique situation. Analysis of wind and pollution roses during exceedance 

days show that the Cowtown monitor is most likely significantly influenced by the cattle feedlots 

located upwind. See Factor 6 discussion of meteorology. 

Table 4. PM2.5 Air Quality Monitoring Data for Pinal County and Nearby Counties 

County Design Value Site AQS ID PM2.5 24-hour Design 

Value 2006-2008 

Cochise Douglas 04-003-1005-1 15 μg/m3

Gila* Payson 04-007-1008-1 23 μg/m3

Maricopa West Phoenix 04-013-0019-1 27 μg/m3

Pima Orange Grove 04-019-0011-1 12 μg/m3

Pinal Cowtown 04-021-3013-1 48 μg/m3

Yavapai** Prescott Valley 04-025-2002-1 12 μg/m3

Yuma** Yuma 04-027-0004-1 21 μg/m3

Santa Cruz*** Nogales 04-023-2002-2 40 μg/m3

*Only two years of data available 

**Only one year of data available 

*** The Nogales planning area in Santa Cruz County, which lies south of Pima County, has been 

designated nonattainment. It is the only other area in Arizona that violates the PM2.5 24-hour NAAQS. 

All of the counties surrounding Pinal County have much lower PM2.5 concentrations. This 

information coupled with the meteorological information and topographic information 

(following) lends support to a finding of predominate local influence over PM2.5 concentrations 

at the Cowtown monitor. 
17 

Figure 8. PM2.5 Monitors and Design Values 
18 

Factor 3: Population density and degree of urbanization (including commercial 

development) 

Table 5 shows the 2005 population and population density for each county in the area being 

evaluated. 

Table 5. Population: Pinal and Surrounding Counties 

County State 

Recommended 

Nonattainment? 

2005 Population 2005 Population 

Density 

(pop/sq mi) 

Pinal* No 240,044 45 

Maricopa No 3,683,481 394 

Cochise No 126,153 20 

Gila No 51,528 11 

Graham No 33,089 7 

La Paz No 20,225 4 

Pima No 925,000 101 

Yavapai No 198,841 24 

Yuma No 181,598 33 

*Arizona submitted its recommendations on December 19, 2007. At that 

time, Pinal County was attaining the 24-hr PM2.5 standard 

Table 6 shows the 2008 population density for municipalities and reservations within Pinal 

County. 

Table 6: Population Density within Pinal County – 2008 

Entity Area in 

Square 

Miles 

2008 

Population Density 

2008 

Population 

Pinal County 

Total 

5,369.6 65.3 350,558 

Apache 

Junction 

34.23 1,108.7 32,776 

Casa Grande 48.17 936 41,152 

Coolidge 5.03 2,447.5 10,261 

Eloy 71.67 225.4 12,750 

Florence 8.29 2,903.1 20,781 

Kearny 2.79 1,177.5 3,297 

Mammoth 1.08 2,339.1 2,573 

City of 

Maricopa 

31.9 1,428.6 45,571 

Queen Creek 25.8 944.2 Pinal Co: 5,700 

Maricopa Co: 18,661 

Total: 24,361 

Superior 1.93 1,766.3 3,335 

Ak Chin 87.2 48.3 1,591 

GRIC** 581.1 37 21,665 

San Carlos 

Apache** 

2,896.6 3.6 10,416 

Tohono 

O’odham** 

4,453 3.1 13,635 

Source: U.S. Census Bureau and ADEQ TSD 
19 

*Maricopa 2008 area from ADEQ PM10 boundary recommendation TSD 

**Population for entire reservation, including portions that lie outside of Pinal County. 

Table 5 illustrates that, with the exception of Maricopa County, Pinal County and other 

surrounding counties are relatively sparsely populated. Maricopa County, which lies to the north 

and includes the Phoenix metro area, has a population density of 394 people per square mile, but 

does not violate the 2006 24-hour PM2.5 NAAQS. As illustrated by Figure 9, about 95% of the 

Pinal County population resides in the more urbanized areas that lie in the western/central 

portion of the County, where a number of relatively densely populated areas are located. Even 

within those more densely populated areas, the numbers of inhabitants are relatively low (see 

Table 6). 

Population data can give an indication of whether it is likely that population-based emissions are 

contributing to PM2.5 levels at the violating monitor. For this area, population density, however, 

does not appear to be a driving factor in the high PM2.5 levels measured at the Cowtown monitor 

in Pinal County. Instead, the violations in this area appear to be contributed to most heavily by 

cattle feedlots and other agricultural activities that in fact are inversely related to the population

density. Therefore, in this area, population and population density are not as relevant to 

evaluating the geographic extent of the area with emissions activities contributing to the 

violations. 
20 

Figure 9. Population Density and PM2.5 Monitors 
21 

Factor 4: Traffic and commuting patterns 

This factor considers the number of commuters in each surrounding county who drive to Pinal 

County, the percent of total commuters in each county who commute to Pinal County, the 

percent of total commuters in each county who commute into the statistical area in which Pinal 

County is located, as well as the total vehicle miles traveled (VMT) for each county, in millions 

of miles. 

Data on commuting illustrate that the majority of Pinal County’s working residents are employed 

within the county. Data from 200012 illustrate that a sizeable number (19,918) commute to 

Maricopa County to the north, with 7,750 commuters entering Pinal from Maricopa County. 

About 2,600 Pinal County residents commute to Pima County to the south, while 1,970 Pima 

County residents commute into Pinal County. The number of commuters to and from other 

surrounding counties is negligible. See Table 7 and Figure 10. 

Table 7. Traffic and Commuting Patterns – 2005 

County State 

Recommended 

Nonattainment? 

2005 

VMT 

(millio

ns of 

miles) 

Number 

Commuting 

to Pinal 

County 

Percent 

Commuting 

to Pinal 

County 

Number 

Commuting 

into 

statistical 

area* 

Percent 

Commuting 

into 

statistical 

area 

Pinal No 3,126 35,960 60.1 55,880 93.4 

Maricopa No 32,392 7,750 0.6 1,389,480 98.9 

Cochise No 1,906 40 0.1 260 0.6 

Gila No 536 330 1.9 1,390 7.9 

Graham No 373 - 0.0 150 1.4 

La Paz No 684 - 0.0 150 1.4 

Pima No 8,759 1,970 0.5 3,810 1.0 

Yavapai No 2,385 30 0.0 3,640 5.4 

Yuma No 1,902 10 0.0 240 0.5 

*Pinal and Maricopa Counties comprise the Phoenix-Mesa-Scottsdale CBSA 

Commuting patterns can indicate the extent of an urban area and can serve as an indicator of 

likely contribution to fine particle concentrations in an area. However, in this area, the technical 

analysis suggests that the violations at the Cowtown monitor are the result of contribution not 

from secondary particles from more distant mobile source emissions, but rather from other types 

of emissions activity closer to the violating monitor. The nature of the PM2.5 violation in Pinal 

County indicates the violations occurring there are driven primarily by nearby stationary and 

area sources of PM2.5. See Factors 1 and 2. Traffic may contribute somewhat to the PM2.5 levels 

on days with violations at the Cowtown monitor, but it does not appear to be one of the major 

factors in the violations. 

Note: The 2005 VMT data used for Tables 7 and 8 of the 9-factor analysis has been derived 

using methodology such as that described in “Documentation for the 2005 Mobile National 

Emissions Inventory,” Version 2, December 2008, prepared for the Emission Inventory Group, 

 

12 Arizona Air Quality Designations Technical Support Document; Boundary Recommendation for the Pinal County 

24-hour PM10 Nonattainment Area, Table 3-6, March 15, 2010. 
22 

U.S. EPA. This document can be found at: at 

ftp://ftp.epa.gov/EmisInventory/2005_nei/mobile_sector/documentation//2005_mobile_nei_versi

on_2_report.pdf

Figure 10. Traffic, Commuting Patterns, and PM2.5 Monitors 

Factor 5. Growth rates and patterns 

This factor considers population growth for 2000-2005 and growth in vehicle miles traveled for 

1996-2005 for Pinal and the surrounding counties, as well as patterns of population and VMT 

growth. Population growth within Pinal County between the years of 2000 and 2008 is also 

reviewed. A county with rapid population or VMT growth is generally an integral part of an 

urban area and likely to be contributing to fine particle concentrations in the area. 

Table 8 below shows population, population growth, VMT and VMT growth between 1996 and 

2005 for Pinal and the surrounding counties. 
23 

Table 8. Population and VMT Values and Percent Change 

Location Population 

(2005) 

Population 

Density 

(2005) 

Population 

% change 

(2000 - 

2005) 

2005 VMT 

(millions 

mi) 

VMT 

% change 

(1996 to 

2005) 

Pinal 240,044 45 32 3,126 54 

Maricopa 3,683,481 394 17 32,392 53 

Cochise 126,153 20 7 1,906 29 

Gila 51,528 11 0 536 6 

Graham 33,089 7 -1 373 32 

La Paz 20,225 4 3 684 48 

Pima 925,000 101 9 8,759 52 

Yavapai 198,841 24 18 2,385 12 

Yuma 181,598 33 13 1,902 38 

Table 9 shows the 2006 and 2008 population density for municipalities within Pinal County. 

Table 9. Population Growth within Pinal County 

Entity Area in 

Square 

Miles 

Population Density Population 

2000 2008 2000 2008 

Pinal County 

Total 

5,369.6 33.5 65.3 179,727 350,558 

Apache 

Junction 

34.23 929.3 1108.7 31,814 32,776 

Casa Grande 48.17 523.7 936 25,224 41,152 

Coolidge 5.03 1,549.1 2,447.5 7,786 10,261 

Eloy 71.67 144.8 225.4 10,375 12,750 

Florence 8.29 2,056.2 2,903.1 17,054 20,781 

Kearny 2.79 805.4 1,177.5 2,249 3,297 

Mammoth 1.08 1,626.5 2,339.1 1,762 2,573 

City of 

Maricopa* 

2000 – 4.04 

2008 – 31.9 

257.6 1,428.6 1,040 45,571 

Queen 

Creek** 

25.8 167.3 944.2 Pinal Co: 119 

Maricopa Co: 4,197 

Total: 4,316 

Pinal Co: 5,700 

Maricopa Co: 18,661 

Total: 24,361 

 

Superior 1.93 1,684.6 1,766.3 3,254 3,335 

Source: U.S. Census Bureau and ADEQ TSD 

*Maricopa 2008 area from ADEQ PM10 boundary recommendation TSD 

** Queen Creek straddles the Pinal and Maricopa County border, with about 23.4% of the city’s area lying within 

Pinal County. The population figures in the table are pro-rated to reflect the proportion of the city that is within each 

county, but density is not pro-rated. 
24 

The State of Arizona has experienced rapid population growth in recent years (26.7% between 

2000 and 2008); however, vast areas remain sparsely inhabited. In Pinal County the population 

increased 82% between 2000 and 2008, with almost all of the population growth occurring in the 

central and western portion of the county. Along with this growth, VMT has also increased 

dramatically. 

Growth in Pinal County may be contributing somewhat to the PM2.5 levels on days with 

violations at the Cowtown monitor; however, it does not appear to be one of the major factors in 

the violations. 

Factor 6. Meteorology 

Like most of Arizona, Pinal County is hot and dry. Average maximum temperatures at the 

Maricopa weather station (part of the National Weather Service Cooperative Network) range 

from 67 degrees Fahrenheit (oF) in January to 107 oF in July, and minimum temperatures from 

25 oF in January to 75 oF in August. The rainiest month is July, with just over an inch of rain; the 

yearly total averages 8 inches. Despite the dryness, there is substantial agriculture in Pinal 

County, supported by irrigation from groundwater and the Central Arizona Project. Weather 

systems typically arrive from the west, except during "monsoon" season, which occurs June 

through August or September, when moisture from the south arrives and creates thunderstorms. 

The wind at the Cowtown monitor is typically from the southeast during the cooler hours of 7 

pm - 6 am, corresponding to downhill drainage flow down the Gila River valley. Flow at other 

times is less consistent, though there can be steady winds from the west in late morning through 

the afternoon, and on occasion from the north or south. While there are periods of high wind and 

gusts, especially during "monsoon" season, wind speeds are most often 3 meters per second 

(m/s) or less, with higher speeds usually from the west. High wind and gusts, especially over 

disturbed desert areas, can lead to substantial fugitive dust emissions. Sometimes there are 

“haboob” dust storms that have the appearance of an approaching “wall of dust,” in which 

visibility is very low and gusts very strong. 

EPA examined available PM and meteorological data in a number of ways to assess the extent to 

which surrounding nearby areas could be contributing to PM2.5 violations at the Cowtown 

monitor. Results of these analyses are presented below in the form of: a) a pollution rose for 

daily PM2.5 levels, b) a graph of the correlation of PM2.5 with PM10 at four monitoring sites in the 

Pinal County area, and c) graphs showing the diurnal pattern of PM10, wind speed, and 

temperature for PM2.5 exceedance days. The potential for transport of PM2.5 from the 

metropolitan Phoenix area to the north was considered in the analyses, given the large number of 

emitting sources and the high population density there. 

a. Pollution rose 

EPA developed a “pollution rose” for the Cowtown site to understand the prevailing wind 

direction and wind speed on the days with highest fine particle concentrations. Figure 11 

categorizes 24-hour PM2.5 values by color: days exceeding 35μg/m3

 are denoted with large red or 
25 

black symbols. Small blue symbols are for days under 30μg/m3

, and intermediate sized yellow 

symbols are between 30 and 35μg/m3. Symbol shape distinguishes time of year the exceedance 

occurred: a circle for the warm season (May through September), and a triangle for the cool 

season (October through April). The center of the figure indicates the location of the air quality 

monitoring site, and distance of the symbol from the center indicates average wind speed on the 

day, with lower wind speeds nearer the center. The angular location of the symbol indicates the 

compass direction from which the average wind was blowing on that day. (Note that, since a 

pollution rose symbol direction is the resultant of 24 hourly winds during each day, a symbol in 

the southwest may be a combination of westerly and southerly flow, for example.) 

 

The pollution rose indicates that most PM2.5 exceedances occur when resultant wind is from the 

southwest through southeast, although there are a number of days with no clear wind direction 

(symbols without fill, near the center), and a few days with wind from the north and northeast. 

There does not seem to be a clear separation between the cool and warm seasons. The highest 

PM2.5 concentrations (black symbols) have wind directions from the south or southwest, and two 

from the north. Only a few days have resultant wind speeds above 8 m/s; the vast majority have 

speeds of 4 m/s or less. Altogether, the pollution rose indicates that PM2.5 exceedances are 

generally not associated with steady strong winds, or with winds from the north. This is evidence 

that the exceedances of the 24-hour PM2.5 standard measured at the Cowtown monitor are likely 

due to local sources. 

Figure 11. Pollution Rose
26 

b. Correlation of PM2.5 and PM10

EPA examined the correlation of daily PM10 with daily PM2.5, and also the correlation of the 

PM2.5/ PM10 ratio with PM2.5, for various monitoring sites in Pinal County and neighboring 

Maricopa County, as illustrated in Figure 12. The Cowtown monitor has a consistent PM2.5/ 

PM10 ratio that is lower than other nearby sites, suggesting that the causes of Cowtown PM2.5

concentrations are different than for other locations. In addition, the Cowtown ratio is 

independent of the PM2.5 level, whereas for other sites, the ratio increases with PM2.5. This 

indicates that the Cowtown monitor is impacted by different PM2.5 sources than other locations. 

The correlation of the PM2.5/ PM10 ratio with PM2.5 concentrations at the Cowtown monitor also 

suggests that PM2.5 and PM10 concentrations at the Cowtown monitoring site are generated by 

the same sources. 

Figure 12. Correlation Between Ratio of PM2.5/ PM10 and PM2.5

c. Diurnal pattern of PM10, wind speed, wind direction, and temperature 

Hourly PM2.5 data are not available for the Cowtown site, but hourly PM10 data are. EPA 

examined the diurnal variation of PM10, wind speed, wind direction, and temperature, together 

with daily PM2.5 values. PM10, wind speed, and temperature for two representative quarters are 

presented in Figures 13 and 14.13 Hourly wind direction for all exceedance days is provided in 

Figure 15. While PM10 is not the same as PM2.5, the correlation of 24-hour PM10 and PM2.5

described above suggests that diurnal PM10 patterns may provide useful information about PM2.5. 

 

13 Appendix B includes meteorological data for all quarters. 
27 

Figure 13. Diurnal Variation of PM10, Wind Speed, and Temperature on PM2.5 Exceedance 

Days in Quarter 1 
28 

Figure 14. Diurnal Variation of PM10, Wind Speed, and Temperature on PM2.5 Exceedance 

Days in Quarter 4 
29 

Figure 15. Wind Vectors on 2006-2008 Cowtown PM2.5 Exceedance Days 
30 

Most of the PM2.5 exceedance days have a very large PM10 "spike" (1000 - 3000 μg/m3

) some 

time in hours 20-23 (Figures 13 and 14, top panel). This spike is independent of wind speed 

(Figures 13 and 14, middle panel), temperature (Figures 13 and 14, bottom panel), or direction 

(Figure 15) during the day. During the rest of the day, PM10 is generally low, though with 

morning excursions on a few days. Thus, the PM10 spike appears to be associated with some 

local activity, possibly at the nearby feedlots. 

A few days (e.g., 2007-10-09) have elevated PM10 after elevated winds (10 m/s); other days have 

high wind, but well before any increase in PM10 levels. However, in general, wind speeds are at 

most 4 m/s, so high PM10 is not typically caused by local wind-generated fugitive dust. 

The height of the PM10 spike is not directly related to the PM2.5 value for the day, despite the 

overall correlation of 24-hour PM10 and PM2.5. High winds do not seem to be the cause of the 

PM2.5 exceedances, though may be a contributing factor in a few cases. 

Approximately half of the PM2.5 exceedance days have steady wind from the north during the 

afternoon (Figure 15). However, the period of northerly wind generally coincides with the 

period of lowest PM10. Quarter 4 includes December 1, 2006, one of the two exceedance days 

shown in the pollution rose (Figure 11) where the resultant wind direction was from the north. 

The hourly PM10 concentrations for 12/1/2006 show the same spike during the hours of 20-23, 

which coincides with wind directions from the south rather than the north (Figure 15). Thus, it is 

unlikely that PM10 transported from the north (i.e., metropolitan Phoenix) is the cause of elevated 

PM10 concentrations. Since daily PM2.5 and PM10 levels rise and fall roughly together at the 

Cowtown site, as described above, this is evidence that PM2.5 levels measured at the Cowtown 

monitoring site are due to local activity. 

The overall correlation between PM2.5 and PM10 at the Cowtown monitoring site, combined with 

the generally low wind speeds, is evidence that the PM2.5 levels are likely due to emissions from 

local sources. 

The fact that wind speeds and PM10 concentrations are low when the wind is from the north is 

evidence that emissions from the north do not contribute to PM2.5 exceedances. This is unlike 

what might have been expected based on the proximity and large emissions of the greater 

Phoenix metropolitan area, but these analyses provide evidence that the Phoenix area does not 

contribute to PM2.5 exceedances at the Cowtown monitor. 

Factor 7. Geography and Topography 

The geography/topography analysis evaluates the physical features of the land that might have an 

effect on the airshed and, therefore, on the distribution of PM2.5 into and within the Pinal County 

area. 

The counties of Yavapai, Gila, Graham, and Cochise, which lie to the north and east of Pinal and 

Maricopa counties, are separated topographically from Pinal County by mountainous terrain, 

which impedes the transport of emissions. This lends weight to EPA’s determination that the 
31 

Yavapai, Gila, Graham, and Cochise counties are unlikely contributors to violations at the 

Cowtown monitor. 

Figure 16 illustrates the general topographic features for Pinal County and the surrounding 

counties. Pinal County itself area has topographical barriers significantly limiting air pollution 

transport within its airshed and from neighboring airsheds, though these barriers are not absolute. 

Therefore, this factor provides some support for EPA’s suggested boundary for the 

nonattainment area. Pinal County generally has fairly low relief and is at around 1,200 feet 

elevation, but it is punctuated by various mountains and ranges having peaks from 3,000 to 5,000 

feet. The mountain ranges generally run southeast-northwest, and form broad desert valleys. In 

the vicinity of the violating monitor, there are the Sacaton Mountains to the east, rising to 2,235 

feet, the Maricopa Mountains to the west to 2,400 feet. Nearest is the southeastern tip of the 

Sierra Estrella Mountains, starting at about 10 miles northwest of the monitor; they have peaks to 

3,000 and 4,500 feet. To the north, between Pinal and Maricopa Counties, are the South 

Mountains rising to 2,500 feet; they run west-southwest to east-northeast unlike most of the 

ranges. They are only 10 miles long, but along with the Sierra Estrella they form a partial barrier 

between Pinal and metropolitan Phoenix to the north. Approximately 50 miles east of the 

violating monitor, the eastern quarter of the county becomes more mountainous, ultimately rising 

to some 6,000 feet near the eastern borders with Gila and Graham Counties. Overall, the 

mountains within the county can redirect winds, and form a partial barrier to transport from the 

eastern portions of the County and from neighboring counties. 

Approximately 12 miles north of the monitor is the Gila River channel, which in this area is dry. 

It descends toward the west-northwest before it joins the Salt River in Maricopa County, and 

ultimately the Colorado River. The general area around the monitor is in the valley of this river, 

which is oriented in the same direction as that of the mountain ranges. As a result, air drainage 

flows towards the northwest are typically seen. 

The presence of topographic barriers both outside and within Pinal County supports EPA’s 

suggested partial county boundary for the nonattainment area and lends further support to a 

designation of “unclassifiable/attainment” to the surrounding counties. 
32 

Figure 16. Topography 
33 

Factor 8: Jurisdictional boundaries 

In evaluating the jurisdictional factor, EPA considered the planning and organizational structure 

of Pinal County, the State of Arizona, and Indian country to ensure that the implementation of 

controls within the prospective nonattainment area can be carried out in a cohesive manner. See 

Figure 17 for jurisdictional boundaries. 

The Arizona Department of Environmental Quality has overall jurisdiction over environmental 

programs in the state of Arizona, as well as jurisdiction over certain source types, including 

smelters, refineries, and coal-fired power plants, and retains authority for regulating emissions 

from agricultural operations. Three Arizona counties, Maricopa, Pima, and Pinal, have their own 

air pollution control programs and operate pursuant to agreements with ADEQ. The lead air 

quality planning agencies responsible for state implementation plans (SIPs) for Maricopa County 

and Pima County are the metropolitan planning organizations (MPO), the Maricopa Association 

of Governments (MAG) and the Pima Association of Governments (PAG), respectively. There is 

no MPO and thus no lead air quality planning agency for SIP purposes in Pinal County. 

Therefore, ADEQ is responsible for developing SIPs for Pinal County. Pinal County has 

permitting authority, and can adopt control measures by rule, but is preempted from adopting 

rules regulating certain categories of sources. 

Four tribes are located in Pinal County. A portion of the Tohono O’odham Nation (TON) lies in 

southeastern Pinal County, south of the proposed nonattainment area. A portion of the San 

Carlos Apache tribal lands lie within the eastern part of Pinal County, east of the proposed 

nonattainment area. Both the TON and San Carlos Apache lands are within the area EPA 

intends to designate “unclassifiable/attainment.” As explained above, EPA is deferring 

designation of the two remaining tribes pending consideration of issues unique to tribal lands and 

completion of formal consultation. The Ak-Chin Indian Community tribal lands lie entirely 

within the County, and are encircled by the new nonattainment area. The Gila River Indian 

Community tribal lands lie to the north of the nonattainment area and straddle the PinalMaricopa boundary. Neither ADEQ nor the counties have jurisdiction over tribal lands. 

Of the four tribes, only the Gila River Indian Community has treatment as a state (TAS) status 

for Clean Air Act section 107 designations, and an air quality monitoring network that reports 

quality-assured data to EPA’s Air Quality System (AQS). None of the tribes currently monitor 

for PM2.5. 
34 

Figure 17. Jurisdictional Boundaries 
35 

Factor 9: Level of control of emission sources 

Under this factor, the existing level of control of emission sources is taken into consideration. 

The emissions data used by EPA in this technical analysis and provided in Table 1 (under Factor 

1) represent emissions levels taking into account any control strategies implemented in Pinal and 

nearby counties before 2005 on stationary, mobile, and area sources. Data are presented for 

PM2.5 components that are directly emitted (carbonaceous PM2.5 and crustal PM2.5) and for 

pollutants that react in the atmosphere to form fine particles (e.g., SO2, NOx, VOC, and 

ammonia). EPA is not aware of any additional information on emissions controls that is relevant 

to assessing sources contributing to the monitored violation. 
A-1 

Appendix A 

Emissions in Pinal County: Primary PM2.5, NOx, NH3, SO2, VOCs. 
A-2 

Pinal County: Primary PM2.5 (includes filterables + condensibles) Sources. 2005 NEI version2. 

Source Category 

Emissions 

(tpy) 

% of Total Primary 

PM2.5Emissions, Pinal County 

Nonpoint 

 Waste Disposal - Open Burning 886 21%

 Agric - Crop Tilling & Livestock Dust 751 18%

 Unpaved Roads 626 15%

 Construction 547 13%

 Wildfires 395 9%

 Indus Process – NEC 220 5%

 Paved Roads 152 4%

 Other Nonpoint 105 2%

Nonroad 

 Non-Road Equipment - Diesel 166 4%

 Planes, Trains, & Ships 64 2%

 Non-Road Equipment - Gasoline 38 1%

Onroad 

 On-Road Vehicles - Diesel 116 3%

 On-Road Vehicles - Gasoline 42 1%

Point 

 Misc. Point 102 2%

TOTAL: 4,210 100%
A-3 

Pinal County: Nitrogen Oxides (NOx) Sources. 2005 NEI version 2. 

Source Category 

Emissions 

(tpy) 

% of Total NOx Emissions, Pinal 

County 

Onroad 

 On-Road Vehicles - Diesel 3,889 31%

 On-Road Vehicles - Gasoline 3,715 30%

Nonroad 

 Planes, Trains, & Ships 2,275 18%

 Non-Road Equipment - Diesel 1,775 14%

 Non-Road Equipment - Gasoline 142 1%

Nonpoint 

 Waste Disposal - Open Burning 235 2%

 Wildfires 113 1%

 Fuel Comb - Industrial Boilers, ICEs 81 1%

 Fuel Comb - Residential Fossil 65 1%

 Other Nonpoint 35 0%

Point 

 Fuel Comb - Electric Utility 173 1%

 Misc. Point 47 0%

TOTAL: 12,545 100%

Pinal County: Ammonia (NH3) Sources. 2005 NEI version 2. 

Source Category 

Emissions 

(tpy) 

% of Total 

NH3Emissions, Pinal 

County 

Nonpoint 

 Livestock Waste 4,344 77%

 Fertilizer Application 845 15%

 Other Nonpoint 75 1%

Onroad 

 On-Road Vehicles - Gasoline 305 5%

 On-Road Vehicles - Diesel 9 0%

Point 

 Fuel Comb - Electric Utility 65 1%

Nonroad 

 Misc. Nonroad 2 0%

TOTAL: 5,646 100%
A-4 

Pinal County: Sulfur Dioxide (SO2) Sources. 2005 NEI version 2. 

Source Category 

Emissions 

(tpy) 

% of Total SO2

Emissions, Pinal County 

Nonroad 

 Non-Road Equipment - Diesel 244 32%

 Planes, Trains, & Ships 163 22%

 Non-Road Equipment - Gasoline 1 0%

Nonpoint 

 Fuel Comb - Industrial Boilers, ICEs 130 17%

 Wildfires 48 6%

 Other Nonpoint 21 3%

Onroad 

 On-Road Vehicles - Diesel 105 14%

 On-Road Vehicles - Gasoline 38 5%

Point 

 Misc. Point 7 1%

TOTAL: 757 100%

Pinal County: Volatile Organic Compounds (VOC) Sources. 2005 NEI version 2. 

Source Category 

Emissions 

(tpy) 

% of Total VOC 

Emissions, Pinal 

County 

Onroad 

 On-Road Vehicles - Gasoline 3,539 38%

 On-Road Vehicles - Diesel 200 2%

Nonroad 

 Non-Road Equipment - Gasoline 1,476 16%

 Non-Road Equipment - Diesel 195 2%

 Planes, Trains, & Ships 96 1%

Nonpoint 

 Wildfires 978 11%

 Gas Stations 687 7%

 Waste Disposal - Open Burning 642 7%

 Solvent - Non-industrial 518 6%

 Surface Coating - Industrial 206 2%

 Miscellaneous Sources 186 2%

 Surface Coating - Architectural 176 2%

 Other Nonpoint 239 3%

Point 

 Misc. Point 80 1%

TOTAL: 9,217 100%
A-5 
B-1 

Appendix B 

Meteorological Data 
B-2 
B-3 
B-4 
B-5 
B-6