Arizona Air Quality Designations 

Technical Support Document 

Boundary Recommendation for the Pinal County 

24-hour PM10 Nonattainment Area 

Air Quality Division 

March 15, 2010 

 
 

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TABLE OF CONTENTS 

Page

EXECUTIVE SUMMARY......................................................................................................... ES-1 

1.0 BACKGROUND....................................... ......................................................................... 1 

2.0 AREA DESIGNATION CRITERIA............... ........................................................................... 2 

3.0 AREA DESIGNATION CRITERIA ANALYSIS FOR THOSE AREAS..............................3 

 RECOMMENDED AS NONATTAINMENT 

 

4.0 AREA DESIGNATION RECOMMENDATIONS ....................................................................... 34 

LIST OF FIGURES 

Page

ES-1 Preliminary PM10 Emissions Inventory for Pinal County – All Sources ................ . ES-4 

3-1 Preliminary PM10 Emissions Inventory for Pinal County – Major Features.................. 4 

3-2 Preliminary PM10 Monitors in Maricopa, Pinal, and Pima Counties................. ............ 6 

3-3 Preliminary PM10 Emissions Inventory for Pinal County – All Sources........................8 

3-4 Preliminary PM10 Emissions Inventory for Pinal County – Onroad Sources ..... ............. 11 

3-5 Preliminary PM10 Emissions Inventory for Pinal County – Onroad Sources – ... ............ 12 

 Paved Roads 

3-6 Preliminary PM10 Emissions Inventory for Pinal County – Onroad Sources – ............13 

 Unpaved Roads 

3-7 Preliminary Emissions Inventory for Pinal County – Agricultural Tilling and..............14 

 Harvesting 

3-8 Preliminary PM10 Emissions Inventory for Pinal County – Portable Sources...............15 

3-9 Preliminary PM10 Emissions Inventory for Pinal County – Industrial Sources.................16 

3-10 Preliminary PM10 Emissions Inventory for Pinal County – Concentrated...................17 

 Animal Feeding Operations 

3-11 Preliminary PM10 Emissions Inventory for Pinal County – Construction Sources............18 

3-12 Preliminary PM10 Emissions Inventory for Pinal County – Off-highway Vehicles..........19 

3-13 Pinal County Population Density 2005............................................................21 

3-14 Pinal County Population Density 2030...........................................................21 
ii

3-15 Land Ownership in Pinal County..................................................................22 

3-16 Pinal County Employment Density 2005........................................................24 

3-17 Pinal County Employment Density 2030........................................................24 

3-18 2006-2008 Pinal County PM10 Exceedances....................................................27 

3-19 2006-2008 Pinal County PM10 Exceedances Days by Month.................................27 

3-20 2006-2008 Pinal County PM10 Annual Exceedance Days.....................................29 

4-1 Recommended Pinal County PM10 Nonattainment Area Boundaries...........................35 

LIST OF TABLES Page

ES-1 Summary of Nine Criteria Analysis for the Proposed Pinal County PM10 .................. ES-3 

 Nonattainment Area 

1-1 History of EPA’s Particulate Matter National Ambient Air Quality Standards ................. 1 

2-1 Criteria for Nonattainment Area Boundary Recommendations.......................................... 2 

3-1 2006-2008 Maximum 24-Hour Average PM10 Compliance............................................... 5 

 

3-2 2007 Pinal County PM10 Emissions Inventory .................... ........................................ 7 

3-3 Pinal County-Supplied Road Inventory and ADT.................... .................................... 9 

3-4 Vehicle Miles Traveled and Emissions for HPMS and Pinal County Roads...............10 

3-5 Population Growth and Density within Pinal County..........................................20 

3-6 Inter-County Employment Commute Statistics for Maricopa and Pinal ....................23 

 Counties 

3-7 Population and Daily Vehicle Miles Traveled in Pinal County.................................. 25 

3-8 Summary of Nine Criteria Analysis for the Proposed Pinal County PM10...................33 

 Nonattainment Area 
1

EXECUTIVE SUMMARY 

In July 1987, the U.S. Environmental Protection Agency (EPA) revised the existing National Ambient Air 

Quality Standard (NAAQS) for particulate matter 10 microns or less (PM10) setting a 24-hour average 

standard of 150μg/m3

. Ambient monitoring data for PM10 collected throughout Pinal County by the Pinal 

County Air Quality Control District (PCAQCD) documents numerous violations of the PM10 NAAQS in 

the western portion of Pinal County. In a letter dated October 14, 2009, EPA notified the Governor that 

Pinal County was being redesignated for nonattainment of the 1987 24-hour PM10 NAAQS and requested 

the State to submit PM10 nonattainment area boundary recommendations for Pinal County within 120 

days. The portion of Pinal County recommended for nonattainment consists of the western and central 

regions of the County where violations of the 24-hour PM10 NAAQS have occurred and where emissions 

sources and activities contributing to those violations are located, as shown in Figure ES-1. The Arizona 

Department of Environmental Quality (ADEQ) recommends the remainder of the County outside of the 

existing Hayden PM10 Nonattainment Area and the Apache Junction portion of the Phoenix Planning Area 

PM10 nonattainment area be designated as attainment/unclassifiable. 

 

This recommendation is based on consideration of the PM10 standard, requirements for designation of 

nonattainment areas, and options available for implementing the standard. This document demonstrates 

the impracticability of and lack of environmental benefit from designating the nonattainment area 

boundary based on EPA’s default definition of all of Pinal County. 

As a new 24-hour PM10 nonattainment planning area, the State is recommending those portions of Pinal 

County shown in Figure ES-1 as the nonattainment planning area for the 24-hour PM10 NAAQS. This 

area excludes Indian Country in the affected portion of Pinal County. 

T1S, R8E 

T2S, R8E 

T3S, R7E 

T3S, R8E 

T4S, R3E-R4E (excluding all lands within the Gila River and Ak-Chin Indian Communities) 

T4S, R8E (excluding all lands within the Gila River Indian Community) 

T5S, R3E (excluding all lands within the Ak-Chin Indian Community) 

T5S, R4E – R8E (excluding all lands within the Gila River and Ak-Chin Indian Communities) 

T6S, R3E – R8E 

T7S, R3E – R8E Sections 1-6 
1

Table ES-1 

Summary of Nine Criteria Analysis for the Proposed Pinal County PM10 Nonattainment Area 

Criteria Factors Supporting the Recommended 

Nonattainment Area Boundary 

Factors Supporting the Exclusion of 

Eastern Portions of Pinal County 

Air Quality 

Data 

The proposed nonattainment area includes 

the locations of the monitors that recorded 

concentrations exceeding the NAAQS. 

Ambient air quality monitors located in the eastern 

and southern region of the County are not violating 

the PM10 NAAQS. 

Emissions 

Data 

The preliminary emissions inventory 

prepared by ADEQ and PCAQD 

determined that the majority of PM10 

emissions originate in the western and 

central regions of the County. 

The preliminary emissions inventory determined 

that sources in the eastern and southern regions of 

the County do not significantly contribute to 

violations in other regions of the County. 

Population 

Density and 

Degree of 

Urbanization 

The urbanized areas in the western and 

central regions of the County are where 95 

percent of the County’s population resides. 

The eastern and southern portions of the County are 

largely undeveloped and have very low population 

densities. 

Traffic and 

Commuting 

Patterns 

The recommended nonattainment area 

includes the rapidly growing urbanized and 

developed areas, the high-traffic Interstate 

corridors, and areas with the highest 

employment densities. 

The number of employers in the eastern portion of 

the County is low and is not projected to 

substantially increase during the potential 

maintenance period (2011-2031). 

Growth Rates 

and Patterns 

Significant growth is projected for 

communities near I-10 and I-8 during the 

potential maintenance period (2011-2031). 

The eastern region of the county has experienced 

limited growth and is not projected significantly 

increase. 

Meteorology The recommended nonattainment area 

includes the agricultural basin region of the 

County where stagnation conditions are 

known to impact PM10 concentrations. 

There are no known meteorology conditions 

specific to the eastern portion of the County known 

to affect PM10 concentrations. 

Geography/ 

Topography 

The recommended nonattainment area is 

predominately located in the basin region of 

the County characterized by open-ended 

valleys with few topographic barriers. 

The eastern portion of the County is characterized 

by rough terrain, steep mountain ranges reaching 

over 7,000 feet in elevation. 

Jurisdictional 

Boundaries 

ADEQ’s recommendation maintains 

jurisdictional cohesiveness and requires no 

new institutional arrangements for 

accomplishing required tasks. 

The eastern portions of Pinal County recommended 

as attainment/unclassifiable designation lack 

significant emission sources or are in the existing 

Hayden PM10 nonattainment area. Inclusion of these 

areas would not help bring the western region of the 

county into attainment. 

Level of 

Control of 

Emission 

Sources 

The Apache Junction area of the County 

included in the Phoenix PM10

Nonattainment Area is subject to stringent 

PM10 control strategies included in the 

Maricopa Association of Governments Five 

Percent Reduction Plan. 

The number of PM10 generating sources in eastern 

Pinal County is minimal. The largest point source in 

the area, ASARCO’s Ray Mine, is included in the 

existing Hayden PM10 Nonattainment Area. The 

operating permit issued by PCAQCD for the mine 

contains control measures sufficient for attaining 

the PM10 NAAQS. Emissions from the mine are 

highly localized and do not affect the recommended 

nonattainment area. 

ES-3 
Figure ES-1 
1

Arizona Air Quality Designations Technical Support Document Boundary 

Recommendation for the Pinal County 24-hour PM10 Nonattainment Area 

1.0 BACKGROUND 

The U.S. Environmental Protection Agency (EPA) is charged with developing air quality standards for 

the protection of human health and the environment. As required by the Clean Air Act (CAA), EPA sets 

primary and secondary National Ambient Air Quality Standards (NAAQS) for six common air pollutants, 

one of which is PM10. Maximum pollution levels or limits that are based on human health are called 

primary standards. Limits intended to prevent environmental and property damage are called secondary 

standards. The CAA requires EPA to assess the latest scientific information and review the NAAQS every 

five years. 

The original exceedance-based 24-hour PM10 standard was adopted in 1987, along with an annual PM10 

standard that compared the PM10 average over 3-calendar years against the numerical standard. The 1987 

24-hour PM10 NAAQS is an "exceedance based" standard, which looks to a 3-calendar-year monitoring 

history and assesses the number of historical exceedances of the 150 microgram-per-cubic-meter (μg/m3

) 

PM10 standard. A monitor that measured three or fewer exceedances based on daily sampling and over a 

three-year period complies with the standard, while one that measures four or more exceedances in a 3-

year period violates the standard. In 1997, the EPA left the annual PM10 standard unchanged, but revised 

the approach to assessing compliance with the 24-hour PM10 standard. The EPA adopted a deterministic 

approach, comparing a 3-year average of the 98th percentile highest 24-hour average from each year 

against the 150 μg/m3 standard. Subsequent litigation, however, resulted in overturning the 1997 PM10

revisions and EPA reverted to assessing compliance based on the 1987 exceedance-based algorithm. 

In September 2006, EPA reviewed the latest scientific information on the health effects of exposure to 

PM10. During the 2006 review period, EPA received comments from external scientific advisors and the 

general public about the science and policy review reports. On September 27, 2006, EPA revised the 1987 

PM10 standards by retaining the existing 24-hour PM10 standard and revoking the Annual PM10 standard; 

accordingly, this nonattainment area boundary recommendation addresses EPA’s 24-hour PM10 standard. 

Table 1-1 

History of EPA’s Particulate Matter NAAQS 

Date EPA Action 

1971 Established Total Suspended Particles Standard (45 microns or less) 

1987 Established 24-hour and Annual PM10 Standards 

1997 Established 24-hour and Annual PM2.5 Standards 

2006 Revoked the Annual PM10 Standard, retained the 24-hour PM10 Standard, and 

lowered the 24-hour PM2.5 Standard from 65 μg/m3

 to 35 μg/m3. 
2

2.0 AREA DESIGNATION CRITERIA 

Section 107(d)(1)(A)(i) of the Clean Air Act (CAA) defines a nonattainment area as “any area that does 

not meet (or that contributes to ambient air quality in a nearby area that does not meet) the national 

primary or secondary ambient air quality standard for the pollutant.” 

In a letter dated October 14, 2009, EPA requested that the State of Arizona determine nonattainment area 

boundaries for a Pinal County PM10 Nonattainment Area. ADEQ conducted a nine factor analysis based 

on the analytical approach established by EPA’s guidance pertaining to the 1997 8-hour ozone NAAQS, 

the 1997 PM2.5 NAAQS, and the 2006 PM2.5 NAAQS.1

 ADEQ assessed these nine factors with respect to 

Pinal County, the default under EPA guidance. ADEQ did consider neighboring counties with respect to 

their potential contribution to nonattainment when evaluating the boundaries of the proposed 

nonattainment area; ADEQ’s analysis of those counties is discussed in Section 3.0. 

To refine nonattainment boundaries to be either larger or smaller boundaries than EPA’s default, the State 

must perform an area-specific analysis that addresses the nine criteria discussed in the EPA guidance 

cited above and listed below in Table 2-1. In addition, the State should affirm that the nonattainment area 

analysis demonstrates that: 1) violations are not occurring in nearby portions that are excluded from the 

recommended area, and 2) the excluded nearby portions do not contain emission sources that contribute 

meaningfully to the observed violations.2

Table 2-1 

Criteria for Nonattainment Boundary Recommendations 

1. Emissions data (location of sources and contribution to PM10 concentrations) 

2. Air quality data 

3. Population density and degree of urbanization (including commercial development) 

4. Traffic and commuting patterns 

5. Growth rates and patterns 

6. Meteorology (weather and air movement patterns) 

7. Geography/topography (mountain ranges or other air basin boundaries) 

8. Jurisdictional boundaries (e.g., counties, air districts, existing nonattainment areas, etc.) 

9. Level of control of emission sources 

 

1

 Memorandum from Robert J. Meyers, Acting Assistant Administrator, ``Area Designations for the Revised 24Hour Fine 

Particle National Ambient Air Quality Standard,'' June 8, 2007.
3

3.0 ANALYSIS OF FACTORS FOR DETERMINING NONATTAINMENT AREA 

 BOUNDARIES 

According to EPA's guidance, the default nonattainment area boundary for areas violating the air quality 

standard or contributing to a violation in a nearby area is the county in which the violating monitor(s) is 

located or where the contributing sources are located. The central and western portions of Pinal County 

recommended as nonattainment are where ambient air monitors have recorded PM10 concentrations that 

violate the 24-hour PM10 NAAQS; and emissions sources that contribute to those violations or were 

contributing to violations in areas without monitors. No sources within the recommended area were 

identified as contributing to an external violation, and no external sources were identified as contributing 

to violations within the recommended area. 

In northern Pinal County, the Apache Junction Township already falls within the Phoenix PM10 planning 

area. Although ADEQ recommends that the surrounding portion of Pinal County be newly designated as 

nonattainment for PM10, ADEQ recommends that no change in the designation status for Apache 

Junction, which will remain regulated as part of the Phoenix urban area. 

Eastern Pinal County, however, contains vast expanses of undeveloped public lands and isolated rural 

communities where violations of the NAAQS have not occurred. Those rugged and sparsely populated 

townships in eastern Pinal County form a buffer between the growing urban and exurban areas in the 

western and central portions of the County that are recommended for PM10 nonattainment, and the 

existing Hayden PM10 Nonattainment Area. ADEQ therefore recommends that those portions of eastern 

Pinal County that are not already designated nonattainment be designated as attainment/unclassifiable. 

What follows is an explanation of how each criterion was addressed in Arizona’s recommendation. Figure 

3-1 (see page 5) illustrates the major features considered when assessing the nine factors for Pinal 

County. 

3.1 Air Quality Data 

This factor considers the 24-hour PM10 concentrations recorded by air quality monitors in Pinal County 

during 2006-2008. The PM10 NAAQS is an exceedance-based standard which is attained when the 

expected number of days per calendar year with a PM10 24-hour average above 150 μg/m3 is equal to or 

less than one. The number of expected exceedances at a site is determined by recording the number of 

exceedances in each calendar year and then averaging them over the past three calendar years; if a 

monitoring site has 3.1 or more observed or estimated exceedances in a three-year period, the monitor is 

in violation of the 24-hour PM10 NAAQS. If PM10 sampling is scheduled less than every day, EPA 

requires the adjustment of observed exceedances to account for those days when a sample was not 

collected; the procedure for this process is described in 40 CFR Part 50, Appendix K, Section 3.1. If less 

than 75 percent valid data completeness occurs in one or more calendar quarters, the monitor can not be 

classified as violating the NAAQS. In the case where there are collocated monitors and the primary 

monitor has data completeness below 75 percent, data substitution from the secondary monitor can not be 

done and compliance with the NAAQS can not be determined. 

Monitoring data for 2006-2008 show that six Pinal County monitors were in violation of the PM10

NAAQS, although outstanding requests for EPA concurrence regarding exceptional events could reduce 

the number of violating monitors to five for the 2006-2008 reference period. These violating monitors are 

clustered in the agricultural basin, which includes the urban and exurban high-growth areas contiguous 

with the Phoenix metropolitan area and along Interstates 8 and 10. Table 3-1 contains monitor data for 

2006-2008; Appendix A contains site summary air quality data record for 2006-2008. 
Figure 3-1 
5

All of the violating monitors are within the portion of Pinal County that the State is recommending as the 

nonattainment area for the 24-hour PM10 NAAQS. Figure 3-2 (see page 7) depicts the locations of PM10

monitors in Maricopa, Pinal, and Pima Counties. 

Table 3-1 

 2006-2008 Maximum 24-Hour PM10 Monitoring Data

Maximum 24-hour 

Averages in μg/m3 Expected Number of Exceedances Site Name 

2006 2007 2008 2006 2007 2008 3-year Average 

Apache Junction Fire Station 73 48 57 0 0 0 0 

Casa Grande Downtown 81 112 74 0 0 0 0 

Casa Grande Downtown b

(opened March 2007) N/A 983a 203 N/A 7.0 3.0 N/A 

Combs School 

(opened 3/20/2007) N/A 970a 270 N/A 44.6 4.0 N/A 

Coolidge Maintenance Yard 106 82 55 0 0 0 0 

Cowtown 

(opened August 2005) 606 759 465 278.2 166.2 145.5 196.6 

Cowtown b 1,079 1,014 609 238.9 190.4 175.3 202.9 

Eloy - County Complex 99 136 109 0 0 0 0 

Mammoth - County Complex 31 40 35 0 0 0 0 

Maricopa - County Complex b 429 724 520 21.2 20.1 6. 1 15.1 

Pinal Air Park 77 113 53 0 0 0 0 

Pinal County Housing 

Complex 153 224 141 0 6.5 0 2.2 

Pinal County Housing 

Complex b 913 2,253 285 33.6 19.5 10.3 20.3 

Riverside Maintenance Yard 83 65 44 0 0 0 0 

Stanfield - County Complex 182 374 201 13.1 39.6 11.8 21.5 

Stanfield - County Complex b 

(opened February 2006) 727a

 1,062 375 26.5 25.2 14.2 N/A 

a indicates the data do not satisfy EPA’s summary criteria, usually meaning less than 75 percent valid data recovery 

available in one or more calendar quarters. 

b Indicates every day/continuous monitoring. 

N/A Indicates data are not available. 

Note: exceedances due to exceptional events that have been concurred on by the EPA are excluded from annual 

statistics. 
Figure 3-2 
7

3.2 Emissions Data 

For this factor, ADEQ developed a preliminary emissions inventory for all of Pinal County. Table 3-2, 

below, contains estimates for each category in tons per year. An analysis of the methodologies used to 

calculate emissions for each category follows in the order as they appear below. Figure 3-3 illustrates the 

distribution of emissions from all sources in Pinal County. 

The preliminary annual emission inventory presented in this document was developed for the purpose of 

defining the boundaries for a proposed nonattainment area. The eventual development of a State 

Implementation Plan (SIP) will require additional, more detailed, inventory development, including shortterm inventory data reflecting the 24-hour span of the controlling PM10 standard. ADEQ found making 

credible estimates for disturbed soils on undeveloped lands and windblown dust difficult to determine for 

the preliminary emissions inventory. The State will characterize and quantify estimates for this category 

when developing an emissions inventory for the PM10 SIP. 

Table 3-2 

Pinal County Preliminary 2007 PM10 Emissions Inventory 

Emission Categories 

Tons 

per 

Year 

Addressed 

in Section 

Onroad 42,130 3.2.1 

Tilling, Harvesting, and Agriculture 2,538 3.2.2 

Stationary Industrial Sources 2,342 3.2.3 

Concentrated Animal Feeding Operations 2,045 3.2.4 

Construction Emissions 1,757 3.2.5 

Portable Industrial Sources 38 3.2.3 

Off-highway Vehicles 23 3.2.6 

Total 50,873 

Decisions on nonattainment boundaries can not be made solely on area wide emissions inventories 

because of the influence that localized sources can have on PM10 concentrations. It is possible for source 

categories that represent a small portion of the area-wide inventory to have a significant impact on either 

a violating monitor or the ambient air in areas where there are no monitors. 
Figure 3-3
9

3.2.1 Onroad Emissions 

Emissions from onroad sources include three categories 1) emissions from exhaust, tire and brake wear on 

paved and unpaved roads; 2) fugitive emissions on paved and unpaved roads; and 3) emissions from 

unpaved shoulders on paved roads. Emission factors for each category and the number of vehicle miles 

traveled (VMT) for all the roads in Pinal County are required in order to estimate emissions. 

The inventory of all the roads in Pinal County come from two sources, Arizona Department of 

Transportation's (ADOT) Highway Performance Monitoring System (HPMS) and a road inventory 

supplied by PCAQCD. The HPMS database provides the annual average daily traffic (AADT) for each 

road segment, which can be used to calculate VMT. The road inventory compiled by PCAQCD was 

developed from the County’s internal records, available municipal records, and from inspection of aerial 

photographs. The unpaved roads covered by that inventory included private roads, agricultural roads, and 

trails. 

For County-supplied roads, ADT volumes were assumed as shown in Table 3-3. For example, for 

County-maintained unpaved roads an average daily volume of 100 trips was used to develop estimates. 

This figure was selected based on traffic counts conducted by PCAQCD on highly-traveled unpaved 

roads and a study conducted near the violating Pinal County Housing (PCH) monitor in 2009. 

For private unpaved roads, an ADT volume of 50 was selected using an estimate of five residential 

dwellings per private unpaved road; the number of trips per dwelling was derived from a study conducted 

by the Texas Traffic Institute which determined that one residence equals an average of 10 trips per day. 

The emissions for each category will be described next. 

 

Table 3-3 

Pinal County-Supplied Road Inventory 

and Average Daily Traffic 

Surface Type ADT 

Paved 100 

County-maintained Unpaved 100 

Asphalt Rock Dust Palliative 100 

Trail 10 

Private Unpaved 50 

Agricultural 4 

1. Emissions from exhaust, tire and brake wear: 

EPA's MOBILE6 was used to determine the appropriate emission factors for this category. The emission 

factor was calculated for each road segment in the HPMS database based on the road classification and 

the vehicle mix. For County-supplied roads, the average emission factor of HPMS road segments was 

assumed. 

The emission factor for each road segment was then multiplied by its VMT to derive exhaust, tire and 

brake wear emissions. 

 

2. Fugitive emissions on paved and unpaved roads: 

To estimate fugitive PM10 emissions for paved and unpaved roads in the HPMS database, the State 

utilized the methods described in EPA's AP-42 guidance to determine the emission factors for this 
10

category. The emission factor for each paved road segment in the HPMS database was determined based 

on silt loading and vehicle weight derived from the vehicle mix. The emission factor for each unpaved 

road segment in the HPMS database was calculated based on silt content and average speed. 

The fugitive emission factor for each road segment was then multiplied by its VMT to derive the fugitive 

emissions. The silt loading value for paved roads was extracted from the Maricopa Association of 

Governments' (MAG) 2007 Five Percent Plan for PM10 for the Maricopa County PM10 Nonattainment 

Area. The silt content value for unpaved roads was extracted from ADOT's 2006 Final Report: 

Identification of Emissions Sources for Pinal County. 

For the paved roads data supplied by PCAQCD, the average emission factor of paved HPMS segments 

was assumed, while the average emission factor of unpaved HPMS segments was assumed for the 

unpaved roads supplied by PCAQCD. 

The emission factor for each road segment was then multiplied by the VMT to derive the fugitive 

emissions. 

3. Emissions from unpaved shoulders on paved roads 

Fugitive emission estimates for unpaved shoulders on paved roads were calculated based on the 

percentage of heavy-duty vehicles traveling on the road segments and the VMT. 

Conclusion 

The State's analysis determined that onroad emissions are the largest emission category in Pinal County. 

Most of the emissions from paved and unpaved roads occur in the western and central regions of the 

County, as shown in Figures 3-4, 3-5, and 3-6. Emissions for this category in 2007 are estimated to be 

41,615 tons per year. Table 3-4 provides a complete summary of emissions estimates for Pinal County. 

 

Table 3-4 

Vehicle Miles Traveled and Emissions for HPMS and Pinal County Roads 

HPMS Roads Pinal Roads Total 

No. of Segments 980 30,647 31,627 

Total Daily VMT 6,612,409 270,439 6,882,848 

Daily Paved VMT 6,591,011 32,359 6,623,370 

Daily Unpaved VMT 21,398 238,080 259,478 

Exhaust, Tire and Brake Wear (tpy) 158 5 163 

Fugitive Emissions - Paved Roads (tpy) 4,600 27 4,627 

Fugitive Emissions - Unpaved Roads (tpy) 3,140 33,589 36,729 

Fugitive Emissions - Unpaved Shoulders (tpy) 97 97 

Total Emissions (tpy) 7,994 33,621 41,615 
Figure 3-4 
Figure 3-5 
Figure 3-6 
14

3.2.2 Cultivated Agriculture Emissions 

In order to estimate emissions for this category, ADEQ analyzed land use throughout the County by 

conducting field surveys and reviewing the most recently available satellite images. GIS was employed to 

calculate the area of agricultural fields. ADEQ used emissions factors developed by the United States 

Department of Agriculture (USDA); PM10 emissions for tilling and harvesting were based on the data from 

the USDA National Agriculture Statistics Service. Total emissions were spatially apportioned to each 

agricultural field based on area size. As shown below in Figure 3-7, most agricultural emissions are located 

in the western and central regions of the County. Agricultural emissions in other regions of the County were 

less than 20 tons per grid cell. Emissions for this category in 2007 are estimated to total 2,538 tons per year.

 

Figure 3-7 
15

3.2.3 Portable and Stationary Industrial Source Emissions 

To determine emissions for portable and stationary industrial sources, ADEQ reviewed the Arizona 

Emissions Inventory System (AEIS) for operating permits issued by ADEQ and PCAQCD. The emissions 

limits established in the operating permits helped ADEQ determine annual emissions for these categories in 

2007. ADEQ was unable to calculate credible process emissions for portable sources. Due to the relatively 

small quantity of emissions estimated for portable sources, when spatially allocated do not meet the 

threshold for depiction in Figure 3-8; for that reason the locations of the sources are depicted on the map. 

Emissions for this category are estimated to total 38 tons per year. The industrial source emitting the 

greatest volume of PM10 emissions in Pinal County is ASARCO’s Ray Mine located near the County’s 

eastern border, as shown in Figure 3-9. This source is permitted by PCAQCD and is located within the 

existing Hayden PM10 Nonattainment Area. Emissions for this category are estimated to total 2,342 tons 

per year, the majority of which are assigned to the ASARCO Ray Mine in eastern Pinal County. 

Figure 3-8 
16

Figure 3-9 
17

3.2.4 Concentrated Animal Feeding Operations (CAFOs) Emissions 

To estimate emissions for this category, ADEQ obtained emission factors from the Western Regional Air 

Partnership’s Fugitive Dust Handbook. Activity levels were obtained from ADEQ’s Water Quality 

Division. An emissions factor of 10.59 pounds per-head per-year (lb/head-yr) was used for beef or calf 

operations; 4.182 lb/head-yr was the emission factor used for dairy, egg layer, and ostrich farm 

operations. After consultation with PCAQCD staff, the activity levels for some feedlots were adjusted for 

realistic emissions levels. ADEQ based these adjustments on field observations and inspections by 

PCAQCD staff. The CAFOs that emit the greatest quantity of emissions are located in the western and 

central regions of the County, as shown in Figure 3-10. Emissions for this category in 2007 are estimated 

to be 2,045 tons per year. 

Figure 3-10 
18

3.2.5 Construction Emissions 

Pinal County’s air quality permits database was used to identify 1,148 dust control permits issued during 

2007. The size and scope of earthmoving activities were also obtained by reviewing the permits database. 

ADEQ used aerial photography to verify earthmoving activities. Construction sites were then coded in 

ADEQ’s GIS database and each site was calculated in total acres. The emissions factors used by ADEQ 

for this category were derived from a 2005 PM10 emissions inventory completed by the Maricopa County 

Air Quality Department.2

 As shown in Figure 3-11, the majority of construction emissions were located in 

high growth areas of the County. Emissions for this category in 2007 are estimated to be 1,757 tons per 

year. 

Figure 3-11 

 

2 http://www.maricopa.gov/aq/divisions/planning_analysis/docs/2005_PM10/05_PM_CH_3_Area.pdf
19

3.2.6 Off-highway Vehicle Emissions 

To estimate emissions for this category, ADEQ obtained the number of titled off-highway vehicles 

(OHVs) in Pinal County from the Arizona Department of Transportation’s Motor Vehicles Division. 

Emission factors were obtained from EPA’s NONROAD model for 2007. Due to the relatively low 

volume of emissions for this category, when spatially allocated there were no grid cells over the 20 tons 

per year threshold; accordingly, ADEQ chose to depict the locations of designated OHV recreation areas, 

as shown below in Figure 3-12. Emissions for this category in 2007 are estimated to be 23 tons per year. 

Figure 3-12 

3.2.7 Conclusion 

After completing the preliminary emissions inventory, ADEQ determined that most ambient PM10

emissions are concentrated in the more developed areas of western Pinal County - with the exception of 

the Ray Mine, which is already included in the Hayden PM10 Nonattainment Area. ADEQ’s 

determination is supported by ambient monitoring data collected by air quality monitors violating the 

NAAQS in the western region of the county. 
20

3.3 Population Density and Degree of Urbanization 

 

Table 3-5 features population estimates for municipalities within Pinal County for 2000 and 2008.3

 The 

population of the County has grown dramatically – 95.1 percent – in the intervening years. Development 

in Pinal County is limited to privately owned areas; most of the land available for development is located 

along the I-8 and I-10 corridors, as shown in Figure 3-15. Approximately 95 percent of the Pinal County 

population lives within this region. Figure 3-13 depicts the population density of Pinal County in 2005; 

Figure 3-14 depicts the County’s projected population density in 2030. It must be noted that the 

residential housing market in Pinal County has been particularly affected by the national economic 

recession, with 1 in 35 homes in foreclosure in 2009.4

 Construction of new homes and commercial 

buildings has slowed considerably. 

Sources: Arizona Department of Economic Security – Population Statistics Unit. 

 

3

 Population estimates were obtained from the Arizona Department of Commerce, Arizona Population Estimates 1980 thru 2009, 

because all State agencies are required to use them pursuant to the Governor’s Executive Order 2009-01, superseding Executive 

Order 95-2. 

4

 Josh Brodesky. “Foreclosure Filings Show No Letup.” Arizona Daily Star 16 October 2009, morning ed.: A17. 5 Square mileages for 2009/2010 were obtained from municipality websites. 6

 Queen Creek straddles the Maricopa/Pinal County border; approximately 23.4 percent of the city’s square miles are within Pinal

County. To estimate a population for the Pinal County portion of Queen Creek, ADEQ divided the 2000 and 2008 population 

estimates by 23.4 percent. 

Table 3-5 

Population Growth and Density within Pinal County 

Entity Area in 

Square 

Miles 

2000 

Area in 

Square 

Miles 

2009/20105

2000 

Population 

Density 

2008 

Population 

Density 

2000 

Population 

2008 

Population 

Pinal County Total 5,369.6 5,369.6 33.5 65.3 179,727 350,558

Apache Junction 34.2 34.2 930.2 1,08.7 31,814 37,917

Casa Grande 53.1 109 475.0 433 25,224 45,116

Coolidge 5.03 65 1,548.5 189.4 7,789 12,311

Eloy 71.7 110 144.7 146.9 10,375 16,163

Florence 8.3 50 1,742.9 481.9 14,466 24,096

City of Maricopa 31.9 43 46.5 831.9 1,482 35,770

Queen Creek6 n/a 26 n/a 214.5 1,010 5,576
21

Figure 3-13 

Pinal County Population Density 2005 

Source: Arizona Department of Transportation. 

Figure 3-14 

Pinal County Population Density 2030 

Ibid. 
Figure 3-15 

Source: PCAQCD. 
23

3.4 Traffic and Commuting Patterns 

This factor considers commuting patterns of residents and commuters to Pinal County. Nearly 80 percent 

of those commuting to work in Pinal County are residents. For the 2006-2008 period, the U.S. Census 

Bureau estimated that Pinal County had a work force population of 101,887. As of July 2008, 226,208 

vehicles were registered in Pinal County; this figure represents an increase of 7 percent from 2007. Table 

3-6 contains data on the number and percentage of those commuting to and within Pinal, Pima, and 

Maricopa Counties; these statistics may be dramatically higher in the 2010 decennial census. Figure 3-16 

depicts Pinal County employment density in 2005; Figure 3-17 depicts projected employment density for 

Pinal County in 2030. The highest employment densities are located in the western region of the county. 

Table 3-6 

Inter-County Employment Commute Statistics for Maricopa and Pinal Counties 

from U.S. Census Bureau, April, 2000 Census 

Employment County Residence County Number of Commuters 

Maricopa Pinal 19,918 

Apache 7 

Cochise 43 

Coconino 0 

Gila 333 

Graham 3 

Greenlee 6 

La Paz 0 

Maricopa 7,751 

Mohave 7 

Navajo 7 

Pima 1,974 

Pinal 35,961 

Santa Cruz 11 

Yavapai 25 

Yuma 13 

Pinal 

Total 46,141 

Pima Pinal 2,601 
24

Source: ADOT.

Figure 3-17 

Pinal County Employment Density 2030 

Ibid.

Figure 3-16 

Pinal County Employment Density 2005 
25

3.5 Growth Rates and Patterns 

Most of the population growth in Pinal County since the year 2000 occurred in the central and western 

region of the County. The catalyst for the explosive growth can be attributed to reasonably priced housing 

near the I-10 corridor between the Phoenix and Tucson MSAs. With explosive growth came an increase 

in the number of vehicles and vehicle miles traveled (VMT) in Pinal County. Figure 3-2 (page 7) depicts 

onroad emissions throughout the County; the map demonstrates that the highest concentrations of onroad 

emissions occur in the proposed nonattainment area. The majority of the increase in VMT has occurred in 

the western half of the County where an estimated 95 percent of the County’s population lives. Table 3-7 

below contains population and VMT growth for Pinal County. 

Sources: Census Bureau and ADOT.

Table 3-7 

Population Growth and Daily Vehicle Miles Traveled in Pinal County 

2000 

Population 

2007 

Population 

Estimate 

Population 

% change 

(2000 - 2007) 

2000 

VMT 

(1000s mi) 

2007 

VMT 

(1000s mi) 

% 

Change

Pinal County 179,727 350,558 95.1% 6,917 10,259 48% 
26

3.6 Meteorology 

Central Arizona experiences periods of significant winds associated with frontal passages, troughs of low 

pressure, summer monsoon storms, and occasional strong pressure gradients. The meteorology associated 

with winds in Pinal County ranges from synoptic scale systems such as frontal passages, strong pressure 

gradients, Mesoscale Convective System (MCS)7

 and regional monsoon storms to micro scale storm cells 

that form locally. 

The frontal passages are typically associated with strong Pacific Northwest low pressure systems that 

develop over the northern Pacific Ocean and move southeast into the western United States. Strong winds 

in advance of cold fronts can reach speeds over 30 miles per hour (mph) which cause significant areas of 

blowing dust in central Arizona. The duration of the strong, gusty winds can last up to eight hours and 

result in elevated hourly PM10 concentrations. The hourly PM10 concentrations associated with frontal 

passages may not reach those precipitated by monsoonal thunderstorms – however – their temporal 

duration can create 24-hr PM10 concentrations which reach the 99th percentile of historical PM10 24-hr 

average data. 

Pressure gradient exceptional/natural events result from strong high pressure building over the western 

United States and low pressure to the east. As the high pressure builds, a pressure differential is created 

that causes strong winds over Arizona. The result is locally-developed blowing dust and dust transported 

from areas surrounding Pinal County. As with frontal passages, duration of strong, gusty winds can last 

several hours. The combination of the long duration of transported dust and locally derived dust 

overwhelm the PM10 monitors. 

The monsoon is a seasonal wind that takes place in the southwestern United States and Northern Mexico 

during the summer months. The typical diurnal winds in central Arizona are ‘drainage’ in nature; in the 

morning, easterly winds that originate in the mountains switch direction to westerly winds in the 

afternoon due to the heating of the desert floor. During a monsoon, however, winds will shift to an 

easterly to southeasterly direction. This is due to a ridge of high pressure that sets up over the Four 

Corners region in northeastern Arizona. The result is an influx of atmospheric moisture from the south 

and east, and storm development, which can be synoptic in nature as large lines of storms form either over 

the northern Arizona or northern Mexico/southern Arizona and move into the central area of Pinal 

County. 

Monsoon thunderstorms can also be local in nature, with the formation of localized monsoon supported 

storm cells. Both monsoon setups can pack significant winds (reaching gusts over 60 mph) that cause dust 

storms to develop, transporting a wall of dust (Haboob) up to hundreds of miles. These storms have dustcausing effects similar to frontal passages and strong pressure gradients. The monsoon “season”, as 

defined by the National Weather Service, starts on June 15th and lasts through September 30th. Haboobs 

are frequent at the beginning of the monsoon and subside as the storm progresses, when measurable 

rainfall normally occurs. Monsoon storm cell(s), however, can create strong enough wind gusts to cause 

blowing dust even after recent precipitation. 

Not all exceedances in Pinal County are wind related: stagnation conditions in the fall and winter occur 

when cold air and the absence of winds trap ambient PM10 in the lower atmosphere. The region of the 

county most impacted by stagnation conditions is the western agricultural basin area of the county. 

Stagnation exceedances tend to have lower PM10 concentrations than exceedances caused by wind events, 

as shown in Figure 3-18. Figure 3-19 illustrates the number of exceedances by month in Pinal County 

during 2006-2008. A complete history of exceedances during 2006-2008 is included in Appendix B. 

 

7

 http://www.weather.gov/glossary/index.php?letter=m 
27

2006-2008 Pinal County PM10 Exceedances 

Average Concentration by Meteorology Type

(Excluding Cowtown)

296

173

0

50

100

150

200

250

300

350

Avg Wind Avg Stagnation

Meteorology Type

PM10 Concentration (ug/m3)

NAAQS

Figure 3-18 

 

Figure 3-19 

2006 through 2008 Pinal County PM10 Exceedance Days by Month

Excluding the Cowtown Monitor

0

1

2

3

4

5

6

7

8

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

2006 2007 2008

Exceedance Day s
28

Handling of Exceptional Meteorological Events 

EPA’s 2007 Final Rule, Treatment of Data Influenced by Exceptional Events established guidelines for 

the review and handling of air quality monitoring data influenced by exceptional events. In this rule, the 

demonstration to exclude data includes a clear causal relationship between the measurement under 

consideration and the event that is claimed to have affected air quality in the area and the exceedance 

would not have occurred “but for” the event. 

EPA notes in the Final Rule that natural events (one form of exceptional events according to the 

definition) may recur, sometimes frequently (e.g. western wildfires). For the purpose of this rule, EPA 

defines “natural event” as an event in which human activity plays little or no direct causal role to the 

event in question. The EPA recognizes that over time, certain human activities may have had some impact 

on the conditions which later give rise to a "natural'' air pollution event. However, EPA does not believe 

that small historical human contributions should preclude an event from being deemed "natural.''. The 

March 22, 2007, EPA-adopted rule supersedes all previous documentation regarding flagging and 

excluding data. 

According to the final rule, exceptional events are events for which the normal planning and regulatory 

process established by the CAA is not appropriate. The rule gives authority to exclude air quality 

monitoring data from regulatory determinations related to exceedances or violations of the NAAQS and 

avoid designating an area as nonattainment, redesignating an area as nonattainment, or reclassifying an 

existing nonattainment area to a higher classification if a State adequately demonstrates than an 

exceptional event has caused an exceedance or violation of a NAAQS. 

The EPA requires States to take reasonable measures to mitigate the impacts of an exceptional event. In 

accordance with the language in the rule, EPA defines the term "exceptional event'' to mean an event that: 

(i) Affects air quality; 

(ii) Is not reasonably controllable or preventable; 

(iii) Is an event caused by human activity that is unlikely to recur at a particular 

location or a natural event; and 

(iv) Is determined by EPA through the process established in the regulations to be 

an exceptional event. 

The PCAQCD reviews of PM10 data, meteorology records, the implementation of local fugitive dust rules, 

and the impact of potential local and regional sources when determining whether a PM10 exceedance(s) is 

covered under exceptional/natural event classification. 

 

In June 2008, PCAQCD submitted documentation for PM10 exceedances that occurred in 2007 that the 

County considered exceptional events. EPA subsequently informed PCAQCD that the submitted 

documentation needed additional information in accordance with the existing rule. In response, PCAQCD 

is currently coordinating with EPA to develop more robust exceptional event demonstrations for events 

that occurred in Pinal County during 2007 and 2008. If EPA concurs with the revised demonstrations, the 

monitoring data flagged in AQS will be excluded from regulatory determinations related to exceedances 

or violations of the 24-hour PM10 NAAQS. PCAQCD is currently reviewing the PM10 exceedances 

flagged in AQS to determine if the events from 2007 and 2008 meet EPA’s criteria for exclusion under 

the 2007 Final Rule. 

The number of exceedance days in Pinal County attributed to high winds in 2007 was 35; the total for 

2008 was 17. Of those wind events, PCAQCD has or will be submitting technical demonstrations for 30 

exceedance dates in 2007 and 15 in 2008. It is important to note that even if EPA were to concur with 
29

every exceptional event demonstration submitted by PCAQCD, Pinal County would still qualify as 

nonattainment for violating the 1987 PM10 NAAQS. Exceedances of the NAAQS attributed to stagnation 

conditions do not qualify for exclusion under the exceptional events final rule. Figure 3-20 shows the 

number of exceedance days in Pinal County during 2006-2008; Figure 3-20 also exhibits the number of 

exceedance days that PCAQCD flagged for exclusion in AQS and the number of stagnation exceedances 

for each year. 

Figure 3-20 

2006 through 2008 Pinal County PM10 Annual Exceedance Days

Classified by Meteorology, Excluding the Cowtown Monitor

0

5

10

15

20

25

30

35

40

45

50

55

2006 2007 2008

Flagged Wind Event Unflagged Wind Event Stagnation

Exceedance Day

3.7 Geography/Topography (Mountain Ranges or other Air Basin Boundaries) 

The topography of Pinal County can best be described as a broad basin, low in elevation, surrounded in 

each direction by mountain ranges. Open-ended valleys characterize the topography of western Pinal 

County. The area does not have geographical or topographical barriers limiting air-pollution transport 

within its airshed. Because PM10 is primarily crustal, transport from outside the valleys is unlikely, 

excluding occasional exceptional events. The elevation of the basin area of Pinal County is approximately 

1,200 feet above sea level. 

The mountain ranges that surround the basin area create complex mountain-valley wind patterns. The 

Estrella Mountains in the northwest portion of the County reach 4,125 feet in elevation and provide a 

buffer between Pinal and Maricopa Counties. In the northern portion of Pinal County, the Superstition 

and San Tan Mountains rise to a height of 5,036 and 3,054 feet, respectively. Near the western border of 

the County, the Table Top Mountains reach 3,392 feet in elevation. To the south, the Black Mountains 

reach 5,577 feet. The Pinal Mountains in western Gila County, near Pinal County’s eastern border, reach 

7,848 feet in elevation. 
30

3.8 Jurisdictional Boundaries (e.g., existing PM10 non-attainment areas) 

When recommending PM10 nonattainment area boundaries, EPA recommends that the State consider 

sources contributing emissions from a broad geographic area. Accordingly, the State chose all of Pinal 

County as a starting point for evaluating boundaries of the proposed nonattainment area. In evaluating the 

jurisdictional boundary factor, the State gave special consideration to nearby areas that are already 

designated as nonattainment for violating the 1987 PM10 NAAQS: the Hayden Moderate PM10

Nonattainment Area and the metropolitan Phoenix Serious PM10 Nonattainment Area. The State also 

considered the authorities of PCAQCD and its responsibilities to facilitate air quality planning and 

implement control measures to attain the standard. It is also important to note that neither the Pima 

Association of Governments (PAG) nor MAG has jurisdiction in Pinal County. Those metropolitan 

planning organizations (MPOs) have been certified to develop air quality plans within those counties 

only. 

Five cities and towns are located in central and western Pinal County: Casa Grande, Coolidge, Eloy, 

Florence and Maricopa. In addition, the Town of Queen Creek straddles Maricopa and Pinal Counties. 

Since all the violating monitors are located in or near all of these towns, the incorporated boundaries of 

these municipalities were taken into account. 

Three Indian Reservations occupy portions of Pinal County: Gila River Indian Community, covering 

372,000 acres, 280,000 acres of which are located in the northwestern part of the County; the nearly 

22,000 acre Ak Chin Indian Community, all of which is located near the Town of Maricopa in western 

Pinal County; and the 2.7 million acre Tohono O’odham Indian Nation, most of which is in Pima County, 

with approximately 275,000 acres in southwestern Pinal County. The State has no jurisdiction over 

Indian Country, and, as such, no recommendation is being made for designations relating to these three 

Indian Reservations. 

3.9 Level of Control of Emission Sources 

Pinal County 

The expansion of “Area A” in 1999 and subsequent legislation adopted by the Arizona Legislature 

required State, County, and regional air quality planning agencies to implement measures for dealing with 

particulate pollution. 

Pinal County is authorized under the Clean Air Act and Arizona Revised Statutes as one of three Arizona 

counties with designated authority for air quality monitoring and permitting. The County manages a 

permitting program that requires stringent control measures. Prior to issuing a permit, PCAQCD uses 

computer modeling to assess the impact of emissions on local ambient air quality. PCAQCD issues 

permits for industrial sources, open burning, dust producing activities, and has an approved Title V 

permitting program. The County also has an approved program in place for the prevention of significant 

deterioration (PSD). The County conducts routine field inspections to verify compliance with permit 

conditions and operates a Countywide monitoring network to determine if the ambient air is meeting the 

24-hour PM10 NAAQS. 

Those areas of Pinal County recommended by the State for designation as attainment/unclassifiable 

include the portions of the County where attainment of NAAQS has been demonstrated. For its analysis, 

ADEQ reviewed available ambient monitoring data and statistics for population density, degree of 

urbanization, traffic volume, commuting patterns, and jurisdictional boundaries. After analyzing these 

criteria, ADEQ concluded these areas of the County are not experiencing or likely causing or contributing 
31

to an exceedance of the PM10 NAAQS. Including these portions of the County in the nonattainment area 

would not help the area reach attainment of the NAAQS. This recommendation for eastern Pinal County 

does not affect the status of the existing Hayden PM10 nonattainment area in that portion of the County; 8

nor does the recommendation for northern Pinal County affect the status of the portion of the County that 

is included in the existing Phoenix Planning Area for PM10, which includes only the 36 square mile 

Apache Junction Township commonly identified as Township 1 North, Range 8 East. 

Pima County 

Although Pima County has a larger population and higher population density, significantly more 

commuters and a greater number vehicle miles traveled than Pinal County, no monitors in the County 

violate the 1987 24-hour PM10 NAAQS. 9

If PM10 emissions originating in Pima County were contributing to violations in Pinal County, the 

monitors closest to the County border would be the most likely to be affected; however, the Pinal 

monitors closest to Pima County are not violating the 24-hour PM10 NAAQS. The Pinal Air Park monitor 

is located directly on the border with Pima County and is not violating; the Mammoth monitor 20 miles 

north of the County border is not violating; and the Eloy monitor, 20 miles north of the County border is 

not violating; however, the Eloy monitor is located in a well developed area and does not appear to be 

affected by sources such as cultivated agriculture and unpaved roads in south Eloy. 

Based on this information, ADEQ recommends leaving unchanged the designation of Pima County as 

attainment/unclassifiable. Including Pima County would not help Pinal County reach attainment of the 

NAAQS and could pose jurisdictional boundary complications. In addition, there are no topographical 

features or meteorological patterns affecting airflow that would support including Pima County in the 

proposed nonattainment area. 

Maricopa County 

One PM10 ambient air quality monitor near the border Maricopa/Pinal County border (the Combs School 

Monitor) has violated the 24-hour PM10 NAAQS, as shown in the major features map on Page ES-2. 

Emissions from Maricopa County may be contributing to violations at that monitor; however, the 

adjoining portion of Maricopa County lies within the Phoenix PM10 Planning Area, which was designated 

as serious nonattainment for PM10 in 1996 based on urbanized area emissions [61 FR 21372].10 

The Maricopa Association of Governments (MAG) submitted a PM10 SIP for the Phoenix area in July 

1999, and a revision of that plan in February 2000. At EPA’s request, MAG submitted another revision, 

the Salt River PM10 SIP Revision, in 2002 that focused on achieving attainment in the Salt River bed area 

of Phoenix. After failing to achieve attainment of the PM10 NAAQS, in December 2007, MAG submitted 

the Five Percent Plan for PM10 for the Maricopa County Nonattainment Area. The Five Percent Plan 

contains 46 control measures designed to reduce PM10 emissions in Area A each successive year by five 

percent, in addition to the best available control measures (BACM) and most stringent measures (MSM) 

already in the serious area plan. In combination, these requirements impose the most stringent 

 

8

 The Hayden PM10 nonattainment area was most recently defined in 72 FR 14422 (3/28/07). 9

 The Rillito portion of Pima County was designated as nonattainment for PM10 by operation of law following the CAA 

amendments of 1990. In October 2006, EPA gave the Rillito Nonattainment Area (RNA) a clean data finding based on several 

years of attaining the PM10 NAAQS. ADEQ submitted a Limited Maintenance Plan for the RNA in June 2008. 10 The 36-square-mile Apache Junction area in the northernmost portion of Pinal County constitutes part of the Phoenix Planning 

Area and was designated with the Phoenix metro area as serious nonattainment for the 24-hour PM10 NAAQS in 1996. As with 

the urban areas of Maricopa County, inclusion of Apache Junction in a greater-Pinal nonattainment area would be redundant and 

would complicate jurisdictional boundaries. 
32

combination of State implementation plan ("SIP") mandates that can be required under the CAA. The 

inclusion of Maricopa County in a Pinal County nonattainment area would be unnecessary, would 

complicate jurisdictional boundaries, and would not help Pinal County reach attainment of the PM10

NAAQS. 

3.10 Nonattainment Area Summary of Criteria Analysis 

ADEQ reviewed the nine criteria outlined in EPA's guidance and determined that the portions of Pinal 

County discussed in this section meet the criteria for inclusion in a PM10 nonattainment area. Table 3-8 

summarizes the data and information supporting the nonattainment area recommendation. 
33

Table 3-8 

Summary of Nine Criteria Analysis for the Proposed Pinal County PM10 Nonattainment Area 

Criteria Factors Supporting the Recommended 

Nonattainment Area Boundary 

Factors Supporting the Exclusion of 

Eastern Portions of Pinal County 

Air Quality 

Data 

The proposed nonattainment area includes 

the locations of the monitors that recorded 

concentrations exceeding the NAAQS. 

Ambient air quality monitors located in the eastern 

and southern region of the County are not violating 

the PM10 NAAQS. 

Emissions 

Data 

The preliminary emissions inventory 

prepared by ADEQ and PCAQD 

determined that the majority of PM10 

emissions originate in the western and 

central regions of the County. 

The preliminary emissions inventory determined 

that sources in the eastern and southern regions of 

the County do not significantly contribute to 

violations in other regions of the County. 

Population 

Density and 

Degree of 

Urbanization 

The urbanized areas in the western and 

central regions of the County are where 95 

percent of the County’s population resides. 

The eastern and southern portions of the County are 

largely undeveloped and have very low population 

densities. 

Traffic and 

Commuting 

Patterns 

The recommended nonattainment area 

includes the rapidly growing urbanized and 

developed areas, the high-traffic Interstate 

corridors, and areas with the highest 

employment densities. 

The number of employers in the eastern portion of 

the County is low and is not projected to 

substantially increase during the potential 

maintenance period (2011-2031). 

Growth Rates 

and Patterns 

Significant growth is projected for 

communities near I-10 and I-8 during the 

potential maintenance period (2011-2031). 

The eastern region of the county has experienced 

limited growth and is not projected significantly 

increase. 

Meteorology The recommended nonattainment area 

includes the agricultural basin region of the 

County where stagnation conditions are 

known to impact PM10 concentrations. 

There are no known meteorology conditions 

specific to the eastern portion of the County known 

to affect PM10 concentrations. 

Geography/ 

Topography 

The recommended nonattainment area is 

predominately located in the basin region of 

the County characterized by open-ended 

valleys with few topographic barriers. 

The eastern portion of the County is characterized 

by rough terrain, steep mountain ranges reaching 

over 7,000 feet in elevation. 

Jurisdictional 

Boundaries 

ADEQ’s recommendation maintains 

jurisdictional cohesiveness and requires no 

new institutional arrangements for 

accomplishing required tasks. 

The eastern portions of Pinal County recommended 

as attainment/unclassifiable designation lack 

significant emission sources or are in the existing 

Hayden PM10 nonattainment area. Inclusion of these 

areas would not help bring the western region of the 

county into attainment. 

Level of 

Control of 

Emission 

Sources 

The Apache Junction area of the County 

included in the Phoenix PM10

Nonattainment Area is subject to stringent 

PM10 control strategies included in the 

Maricopa Association of Governments Five 

Percent Reduction Plan. 

The number of PM10 generating sources in eastern 

Pinal County is minimal. The largest point source in 

the area, ASARCO’s Ray Mine, is included in the 

existing Hayden PM10 Nonattainment Area. The 

operating permit issued by PCAQCD for the mine 

contains control measures sufficient for attaining 

the PM10 NAAQS. Emissions from the mine are 

highly localized and do not affect the recommended 

nonattainment area. 
34

4.0 AREA DESIGNATION RECOMMENDATIONS 

ADEQ demonstrated in the preceding analysis that the western and central regions of Pinal County should 

be designated as nonattainment for the 1987 24-hour PM10 NAAQS. The proposed Pinal County PM10 

nonattainment area encompasses all or part of those townships listed below. Those sections of Pinal 

County not listed are recommended as attainment/unclassifiable. 

As a new 24-hour PM10 nonattainment planning area, the State is recommending those portions of Pinal 

County shown in Figure 4-1 as the nonattainment planning area for the 24-hour PM10 NAAQS. This area 

excludes Indian Country in the affected portion of Pinal County. 

T1S, R8E 

T2S, R8E 

T3S, R7E 

T3S, R8E 

T4S, R3E-R4E (excluding all lands within the Gila River and Ak-Chin Indian Communities) 

T4S, R8E (excluding all lands within the Gila River Indian Community) 

T5S, R3E (excluding all lands within the Ak-Chin Indian Community) 

T5S, R4E – R8E (excluding all lands within the Gila River and Ak-Chin Indian Communities) 

T6S, R3E – R8E 

T7S, R3E – R8E Sections 1-6 
Figure 4-1 
Appendix A 

2006-2008 Summary of Pinal County Ambient PM10 Monitoring Data 
37

This page is intentionally blank
Appendix A – 2006-2008 Summary Pinal County PM10 Monitoring Data ( in μg/m3) 

Year Monitor # of Observations Max 24-hour Concentration 2nd Highest Concentration 3rd Highest Concentration 4th Highest Concentration 

2006 Apache Jct. Fire Station 59 73 53 43 42 

Casa Grande 60 81 81 81 72 

Coolidge 58 106 84 83 80 

 Cowtown 57 606 531 510 460 

Eloy 55 99 96 94 79 

Mammoth 55 31 28 26 26 

 Maricopa 361 429 389 330 329 

Pinal Air Park 57 77 67 67 62 

 Pinal County Housing 58 153 152 141 126  Pinal County Housing E. 58 210 170 158 138  Pinal County Housing TEOM 356 913 763 552 432 

Riverside 56 83 45 43 38 

 Stanfield 58 182 161 148 140  Stanfield TEOM 327 727 469 353 251 

2007 Apache Jct. Fire Station 54 48 40 39 29 

Casa Grande 57 112 80 69 64 

Combs School 282 970 867 521 385 

Coolidge 57 82 76 74 73 

Cowtown 55 759 490 396 383 

Eloy (620 N. Main St.) 10 46 36 33 33 Eloy (801 N. Main St.) 50 136 127 96 95 

Mammoth 56 40 29 26 26 Maricopa 363 724 525 332 329 

Pinal Air Park 57 113 61 60 57 

Pinal County Housing 59 224 113 110 99 

Pinal County Housing E. 60 341 145 140 120 

Pinal County Housing TEOM 354 2,253 1,839 448 434 

Riverside 56 65 53 49 49 

Stanfield 58 374 350 292 249 

Stanfield TEOM 358 1,062 482 360 357 

2008 Apache Jct. Fire Station 45 57 32 32 31 

Casa Grande 44 74 54 42 40 

 Combs School 366 270 195 192 171 

Coolidge 45 55 53 52 50 

 Cowtown 60 465 373 354 339 

Eloy 40 109 63 61 58 

Mammoth 44 35 32 27 27 

 Maricopa 361 520 317 213 170 

Pinal Air Park 46 53 42 42 42 

Pinal County Housing 44 141 75 69 68 

 Pinal County Housing E. 46 245 99 83 82  Pinal County Housing TEOM 357 285 274 265 221 

Riverside 44 44 37 36 36 

 Stanfield 61 201 185 149 128  Stanfield TEOM 363 375 364 323 264 
This page is intentionally blank. 
40

Appendix B 

2006-2008 Summary of Pinal County PM10 Exceedances 
41

This page is intentionally blank. 
2006 Pinal County PM10 Exceedances

 48 Exceedance days (19 – stagnation, 28 – wind, combo – 1)

Date Day of Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

1/5/06 Thursday PCH (TEOM) 04-021-3011 (3) 187.5 W1/7/06 Saturday PCH (TEOM) 04-021-3011 (3) 158.2 Stagn

1/12/06 Thursday PCH (TEOM) 04-021-3011 (3) 164.3 Stagn1/13/06 Friday Maricopa 04-021-3010 (3) 174.6 Stagn1/18/06 Wednesday PCH (TEOM) 04-021-3011 (3) 172.8 Stagn

Maricopa 04-021-3010 (3) 191.1 1/19/06 Thursday PCH (TEOM) 04-021-3011 (3) 171.9 W

1/25/06 Wednesday PCH (TEOM) 04-021-3011 (3) 177.6 W

PCH (TEOM) 04-021-3011 (3) 204.6 2/4/06 Saturday PCH east 04-021-3011 (2) 158 Stagn

PCH (TEOM) 04-021-3011 (3) 366.2 2/6/06 Monday Stanfield 04-021-3008 (3) 198.7 W

2/8/06 Wednesday PCH (TEOM) 04-021-3011 (3) 157.7 W2/9/06 Thursday PCH (TEOM) 04-021-3011 (3) 222.3 Stagn

PCH (TEOM) 04-021-3011 (3) 432.1 

2/15/06 Wednesday Maricopa 04-021-3010 (3) 389 

Stanfield 04-021-3008 (3) 248.4 

W

2/17/06 Friday PCH (TEOM) 04-021-3011 (3) 164.3 Stagn2/18/06 Saturday PCH (TEOM) 04-021-3011 (3) 164.1 Stagn

Maricopa 04-021-3010 (3) 190.4 3/8/06 Wednesday PCH (TEOM) 04-021-3011 (3) 173.1 W

3/10/06▲ Friday Maricopa 04-021-3010 (3) 289.6 W

PCH (TEOM) 04-021-3011 (3) 552.4 

Maricopa 04-021-3010 (3) 329.6 

▲Included with ADEQ NEAP to EPA 
2006 Pinal County PM10 Exceedances 

Date Day of Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

PCH (TEOM) 04-021-3011 (3) 336.9 

5/16/06 Tuesday Stanfield 04-021-3008 (3) 205.9 

Maricopa 04-021-3010 (3) 187.1 

W

5/17/06 Wednesday PCH (TEOM) 04-021-3011 (3) 203.3 W

5/22/06

▲ Monday Maricopa 04-021-3010 (3) 173.2 W

6/1/06 Thursday Stanfield 04-021-3008 (3) 160.6 Stagn

6/2/06

▲ Friday Maricopa 04-021-3010 (3) 231.7 Co

6/4/06 Sunday Stanfield 04-021-3008 (3) 164.9 W

6/6/06

▲ Tuesday Stanfield 04-021-3008 (3) 237.5 W

6/24/06 Saturday Maricopa 04-021-3010 (3) 208.4 W

PCH (TEOM) 04-021-3011 (3) 762.8 

6/25/06 Stanfield 04-021-3008 (3) 468.8 

▲ Sunday 

Maricopa 04-021-3010 (3) 329.1 

W

Maricopa 04-021-3010 (3) 429 6/26/06 Monday Stanfield 04-021-3008 (3) 167.3 W

PCH (TEOM) 04-021-3011 (3) 393.7 7/4/06 Tuesday PCH east 04-021-3011 (2) 210 W

Stanfield 04-021-3008 (3) 237.4 7/15/06 Saturday Maricopa 04-021-3010 (3) 204.5 W

PCH (TEOM) 04-021-3011 (3) 268.7 7/16/06 Sunday PCH east 04-021-3011 (2) 170 W

7/18/06 Tuesday PCH (TEOM) 04-021-3011 (3) 186.7 W7/25/06 Tuesday PCH (TEOM) 04-021-3011 (3) 237.7 W8/21/06 Monday Maricopa 04-021-3010 (3) 218 W10/5/06 Thursday Maricopa 04-021-3010 (3) 159.5 Stagn

10/19/06 Thursday Stanfield 04-021-3008 (3) 162.5 Stagn

11/6/06 Monday Stanfield 04-021-3008 (3) 164.9 Stagn

11/13/06 Monday PCH (TEOM) 04-021-3011 (3) 158.1 Stagn11/17/06 Friday PCH (TEOM) 04-021-3011 (3) 246.5 Stagn

▲Included with ADEQ NEAP to EPA 
2006 Pinal County PM10 Exceedances 

Date Day of Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

11/18/06 Saturday Maricopa 04-021-3010 (3) 155 Stagn

PCH (TEOM) 04-021-3011 (3) 257.6 11/29/06 Wednesday Maricopa 04-021-3010 (3) 250.1 W

12/3/06 Sunday PCH (TEOM) 04-021-3011 (3) 294.3 W12/4/06 Monday Stanfield 04-021-3008 (3) 224.4 W

12/12/06 Tuesday PCH (TEOM) 04-021-3011 (3) 167.4 Stagn12/13/06 Wednesday PCH (TEOM) 04-021-3011 (3) 155.7 Stagn

PCH (TEOM) 04-021-3011 (3) 175.3 12/14/06 Thursday Stanfield 04-021-3008 (3) 155.6 Stagn

PCH (TEOM) 04-021-3011 (3) 182.9 

12/15/06 Friday Stanfield 04-021-3008 (3) 162.2 

Maricopa 04-021-3010 (3) 156.7 

Stagn

Maricopa 04-021-3010 (3) 202.6 

12/16/06 Saturday PCH (TEOM) 04-021-3011 (3) 202.5 

Stanfield 04-021-3008 (3) 194.1 

W

12/27/06 Wednesday Stanfield 04-021-3008 (3) 170.8 W

▲ Included with ADEQ NEAP to EPA 
2007 Pinal County PM10 Exceedances

 52 Exceedance days (17 – stagnation, 34 – wind, combo – 1)

Date 

Day of 

Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

Stanfield 04-021-3008 (3) 260 

2/23/07* Friday Stanfield 04-021-3008 (1) 248.3 

PCH (TEOM) 04-021-3011 (3) 189.4 

W

3/4/07* Sunday PCH (TEOM) 04-021-3011 (3) 241.7 W

Combs 04-021-3009 (3) 273.2 3/21/07* Wednesday PCH (TEOM) 04-021-3011 (3) 184.3 W

Stanfield 04-021-3008 (3) 482.3 

3/27/07*† Tuesday Maricopa 04-021-3010 (3) 268.7 

Combs 04-021-3009 (3) 170.1 

W

PCH (TEOM) 04-021-3011 (3) 447.7 

PCH east 04-021-3011 (2) 341 

PCH 04-021-3011 (1) 224.1 

Stanfield 04-021-3008 (2) 349.9 Stanfield 04-021-3008 (3) 347.7 

Maricopa 04-021-3010 (3) 259.9 

Casa Grande 04-021-0001 (3) 221.1 

4/12/07*† Thursday 

Combs 04-021-3009 (3) 160.2 

W

4/15/07* Sunday PCH (TEOM) 04-021-3011 (3) 221.4 W

Maricopa 04-021-3010 (3) 525.1 4/28/07* Saturday Stanfield 04-021-3008 (3) 360.1 W

PCH (TEOM) 04-021-3011 (3) 2,252.8 5/1/07* Tuesday Combs 04-021-3009 (3) 214.6 WPCH (TEOM) 04-021-3011 (3) 434 

Combs 04-021-3009 (3) 326.2 

5/8/07* 

Tuesday 

Stanfield 04-021-3008 (3) 206.1 

W

* PCAQCD flagged exceptional/natural event †ADEQ flagged exceptional/natural event
2007 Pinal County PM10 Exceedances 

Date 

Day of 

Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

5/12/07 Saturday PCH (TEOM) 04-021-3011 (3) 205.1 W5/16/07 Wednesday Combs 04-021-3009 (3) 167.8 W

PCH (TEOM) 04-021-3011 (3) 414.2 

Combs 04-021-3009 (3) 360.5 

Stanfield 04-021-3008 (3) 273.4 6/6/07*† Wednesday 

Maricopa 04-021-3010 (3) 213.4 

W

Stanfield 04-021-3008 (2) 291.8 Stanfield 04-021-3008 (3) 285.5 

Combs 04-021-3009 (3) 237.4 6/11/07* Monday 

Maricopa 04-021-3010 (3) 158.3 

W

6/14/07 Thursday Stanfield 04-021-3008 (3) 170.3 Stag6/15/07 Friday Combs 04-021-3009 (3) 171.8 Stag6/17/07 Sunday Stanfield 04-021-3008 (2) 182.9 Combo (wind 6/18/07 Monday Combs 04-021-3009 (3) 208.7 Stag

Combs 04-021-3009 (3) 211.6 7/5/07* Thursday PCH (TEOM) 04-021-3011 (3) 196.7 WCombs 04-021-3009 (3) 521.4 

Stanfield 04-021-3008 (3) 347.6 

Casa Grande 04-021-0001 (3) 255.7 7/6/07* Friday 

Maricopa 04-021-3010 (3) 232 

W

Stanfield 04-021-3008 (3) 251 

7/16/07* Monday Combs 04-021-3009 (3) 223.8 

PCH (TEOM) 04-021-3011 (3) 199.3 

W

PCH (TEOM) 04-021-3011 (3) 1,838.6 

Stanfield 04-021-3008 (3) 1,062.2 

Casa Grande 04-021-0001 (3) 983.4 

Combs 04-021-3009 (3) 866.9 

7/19/07*† Thursday 

Maricopa 04-021-3010 (3) 724.4 

W

7/23/07* Monday Combs 04-021-3009 (3) 160.9 W

* PCAQCD flagged exceptional/natural event †ADEQ flagged exceptional/natural event
2007 Pinal County PM10 Exceedances 

Date 

Day of 

Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

Maricopa 04-021-3010 (3) 331.7 

8/13/07*† Monday Combs 04-021-3009 (3) 248.4 

PCH (TEOM) 04-021-3011 (3) 202.6 

W

Combs 04-021-3009 (3) 969.5 

Maricopa 04-021-3010 (3) 249.4 

Stanfield 04-021-3008 (2) 247.9 

PCH (TEOM) 04-021-3011 (3) 184.4 

8/16/07*† Thursday 

Casa Grande 04-021-0001 (3) 163.6 

W

Combs 04-021-3009 (3) 230.9 

8/23/07*† Thursday Stanfield 04-021-3008 (3) 216.2 

Maricopa 04-021-3010 (3) 203.8 

W

Combs 04-021-3009 (3) 197.7 8/24/07* Friday Casa Grande 04-021-0001 (3) 188.2 Carryo

PCH (TEOM) 04-021-3011 (3) 253.9 8/29/07* Wednesday Stanfield 04-021-3008 (3) 159.4 W

Combs 04-021-3009 (3) 283 8/30/07* Thursday Maricopa 04-021-3010 (3) 158.5 W

9/1/07* Saturday Maricopa 04-021-3010 (3) 197.5 W

Combs 04-021-3009 (3) 296.9 

10/5/07*† Friday Stanfield 04-021-3008 (3) 177.4 

Maricopa 04-021-3010 (3) 157.5 

W

10/8/07 Monday Combs 04-021-3009 (3) 167 Stag10/9/07 Tuesday Combs 04-021-3009 (3) 166 Stag

10/10/07 Wednesday Combs 04-021-3009 (3) 187.7 Stag10/11/07 Thursday Maricopa 04-021-3010 (3) 189.3 Stag10/12/07 Friday Maricopa 04-021-3010 (3) 170.6 Stagnation (PM10 hourly p

wind was only 13 m

10/16/07 Tuesday Maricopa 04-021-3010 (3) 213 Carryov

* PCAQCD flagged exceptional/natural event †ADEQ flagged exceptional/natural event
2007 Pinal County PM10 Exceedances 

Date 

Day of 

Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

Stanfield 04-021-3008 (3) 186.6 10/16/07* Tuesday Combs 04-021-3009 (3) 164.8 W

Combs 04-021-3009 (3) 207.8 Co

10/19/07 Friday Maricopa 04-021-3010 (3) 166.6 Stag

Stanfield 04-021-3008 (2) 397.1 Stanfield 04-021-3008 (3) 356.8 

Maricopa 04-021-3010 (3) 328.9 10/21/07*† Sunday 

Combs 04-021-3009 (3) 166.2 

W

10/23/07* Tuesday Stanfield 04-021-3008 (3) 184 W

10/24/07*† Wednesday Combs 04-021-3009 (3) 385.2 W

10/26/07 Friday Combs 04-021-3009 (3) 157.3 Stag

10/29/07* Monday Maricopa 04-021-3010 (3) 156.2 W

11/3/07 Saturday Stanfield 04-021-3008 (3) 176.9 Stag11/5/07 Monday Stanfield 04-021-3008 (3) 159.1 Stag11/6/07 Tuesday PCH (TEOM) 04-021-3011 (3) 164.8 Stag

Stanfield 04-021-3008 (3) 246.6 

PCH (TEOM) 04-021-3011 (3) 217.2 

Combs 04-021-3009 (3) 190.6 

Casa Grande 04-021-0001 (3) 172 

11/15/07* Thursday 

Maricopa 04-021-3010 (3) 162.6 

W

11/21/07 Wednesday PCH (TEOM) 04-021-3011 (3) 181.4 Stag11/28/07 Wednesday Combs 04-021-3009 (3) 170.2 Stag

PCH (TEOM) 04-021-3011 (3) 272 

12/7/07* Friday Stanfield 04-021-3008 (3) 257.1 

Casa Grande 04-021-0001 (3) 156.5 

W

12/25/07* Tuesday Stanfield 04-021-3008 (3) 298.2 W

* PCAQCD flagged exceptional/natural event †ADEQ flagged exceptional/natural event 
2008 Pinal County PM10 Exceedances 

21 Exceedance days [5 stagnation, 16 wind] 

Date Day of Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

PCH (TEOM) 04-021-3011 (3) 264.9 

PCH East 04-021-3011 (2) 245 

Stanfield 04-021-3008 (3) 255.3 1/1/08* Tuesday 

Stanfield 04-021-3008 (1) 185 

Wind from Strong 

(Max. wind s

4/26/08 Saturday Stanfield 04-021-3008 (3) 207.5 Stagn5/10/08 Saturday Stanfield 04-021-3008 (3) 161.7 Stagn

5/15/08* Thursday PCH (TEOM) 04-021-3011 (3) 221.1 Storm Outflow Winds (M

Stanfield 04-021-3008 (3) 323.0 

Maricopa 04-021-3010 (3) 317.7 

PCH (TEOM) 04-021-3011 (3) 273.8 

Combs 04-021-3009 (3) 170.7 

5/21/08*† Wednesday 

Casa Grande 04-021-0001 (3) 164.2 

Cold Frontal Passage (M

7/1/08*† Tuesday PCH (TEOM) 04-021-3011 (3) 159.2 Monsoon Storm Outflow 

7/3/08* Thursday Stanfield 04-021-3008 (3) 157.8 Monsoon Storm Outflow 

Stanfield 04-021-3008 (3) 364.3 8/7/08* Thursday Maricopa 04-021-3010 (3) 213.3 Monsoon Storm Outflow 

8/15/08* Friday PCH (TEOM) 04-021-3011 (3) 204.1 Monsoon Storm Outflow 

9/8/08* Monday Stanfield 04-021-3008 (3) 264.2 Monsoon Storm Outflow 

PCH (TEOM) 04-021-3011 (3) 217.1 

Casa Grande 04-021-0001 (3) 202.5 

Combs 04-021-3009 (3) 194.7 

Stanfield 04-021-3008 (3) 178.2 

9/11/08* Thursday 

Maricopa 04-021-3010 (3) 170.4 

Monsoon Storms Outflow 

9/29/08* Monday Combs 04-021-3009 (3) 192.1 Wind from Strong 

(Max. wind s

10/11/08* 

Saturday Maricopa 04-021-3010 (3) 157.0 

Strong low pr

Max. wind s

* PCAQCD flagged exceptional/natural event †ADEQ flagged exceptional/natural event (ADEQ flagging up to 7/4/08)
2008 Pinal County PM10 Exceedances 

Date Day of Week Site AQS # (POC) 

PM10 24-hr Average 

Concentration (ug/m3) 

Weath

(Wind, Stagna

Stanfield 04-021-3008 (3) 212.6 

10/27/08* Monday Stanfield 04-021-3008 (1) 201 

Maricopa 04-021-3010 (3) 159.4 

Pressure gradient/b

(Max. wind s

PCH (TEOM) 04-021-3011 (3) 178.0 10/29/08 Wednesday Stanfield 04-021-3008 (3) 162.1 Stagn

10/31/08 Friday PCH (TEOM) 04-021-3011 (3) 159.3 Stagn

Maricopa 04-021-3010 (3) 520.3 

Stanfield 04-021-3008 (3) 375.1 

PCH (TEOM) 04-021-3011 (3) 285.2 

Combs 04-021-3009 (3) 270.0 

11/9/08* Sunday 

Casa Grande 04-021-0001 (3) 182.9 

Wind from str

(Max. wind s

11/15/08* Saturday Stanfield 04-021-3008 (3) 240.7 Wind from strong 

(Max. wind s

11/20/08 Thursday PCH (TEOM) 04-021-3011 (3) 160.6 Stagn

11/21/08* Friday Stanfield 04-021-3008 (3) 178.6 Wind from strong 

(Max. wind s

12/13/08* Saturday Stanfield 04-021-3008 (3) 178.2 Wind from str

(Max. wind s

 * PCAQCD flagged exceptional/natural event  †ADEQ flagged exceptional/natural event (ADEQ flagging up to 7/4/08) 
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