Technical Support Document for the State of Arizona - Page 1 of 21

Technical Support Document for 2008 Ozone NAAQS Designations

Arizona

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

The table below identifies the areas and associated counties or parts of counties in Arizona that EPA is

designating as nonattainment for the 2008 ozone national ambient air quality standards (2008 NAAQS). 

In accordance with section 107(d) of the Clean Air Act, EPA must designate an area “nonattainment” if 

it is violating the 2008 ozone NAAQS or if it is contributing to a violation of the 2008 ozone NAAQS in 

a nearby area. The technical analyses supporting the boundaries for the individual nonattainment areas 

are provided below.

Nonattainment Areas in Arizona

Area 

Arizona’s Recommended 

Nonattainment Counties EPA’s Nonattainment Counties

Phoenix-Mesa, AZ* Maricopa County (partial)

Pinal County (partial)

Maricopa County (partial)

Pinal County (partial)

*The Phoenix-Mesa area includes areas of Indian country of federally recognized tribes. Table 1 in the 

Phoenix-Mesa nonattainment area identifies the areas of Indian country of each tribe that EPA is 

designating as part of the nonattainment area.

Designation of a state area may also affect Indian country. Areas of Indian country are located within the 

boundaries of the counties EPA is including as the Phoenix-Mesa nonattainment area. Designation of 

areas of Indian country is discussed further in the following technical analysis. All tribes are being

designated in accordance with two guidance documents finalized in 2011 by EPA’s Office of Air 

Quality, Planning, and Standards: Guidance to Regions for Working with Tribes during the National 

Ambient Air Quality Standard (NAAQS) Designations Process1 and the Policy for Establishing Air 

Quality Designations for Distinct Areas of Indian Country (EPA Tribal Designations Policy)2

; in 

addition to EPA’s Policy on Coordination and Consultation with Indian Tribes3

.. EPA has carefully 

evaluated tribal recommendations. More information can be found under the jurisdictional boundaries 

section, below.

EPA is designating the remaining counties, portions of counties, and areas of Indian country in Arizona 

that are not listed in the table above as “unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analysis below provides the basis for nonattainment area boundaries. It relies on our analysis of 

which monitors are violating the 2008 ozone NAAQS, based on certified air quality monitoring data

from 2008-2010, and an evaluation of whether nearby areas are contributing to such violations. EPA 

has evaluated contributions from nearby areas based on a weight of evidence analysis considering the 

factors identified below. EPA issued guidance on December 4, 2008 that identified these factors as ones 

 1 http://www.epa.gov/ttn/caaa/t1/memoranda/20120117naaqsguidance.pdf

2 http://www.epa.gov/ttn/caaa/t1/memoranda/20120117indiancountry.pdf

3 http://www.epa.gov/tp/pdf/cons-and-coord-with-indian-tribes-policy.pdf
Technical Support Document for the State of Arizona - Page 2 of 21

EPA would consider in determining nonattainment area boundaries and recommended that states 

consider these factors in making their designations recommendations to EPA4: 

1. Air quality data (including the design value calculated for each federal reference method (FRM)

or federal equivalent method (FEM) monitor in the area);

2. Emissions and emissions-related data (including location of sources and population, amount of 

emissions and emissions controls, and urban growth patterns);

3. Meteorology (weather/transport patterns);

4. Geography and topography (mountain ranges or other basin boundaries); and

5. Jurisdictional boundaries (e.g., counties, air districts, existing nonattainment areas, Indian 

country, metropolitan planning organizations (MPOs)).

Ground-level ozone generally is not emitted directly into the air, but is created by chemical reactions 

between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. 

Because NOx and VOC emissions from a broad range of sources over a wide area typically contribute to 

violations of the ozone standards, EPA believes it is important to consider whether there are contributing 

emissions from a broad geographic area. Accordingly, EPA chose to examine the five factors with 

respect to the larger of the Combined Statistical Area (CSA) or Core Based Statistical Area (CBSA) 

associated with the violating monitor(s).

5 All data and information used by EPA in this evaluation are 

the latest available to EPA and/or the latest information provided to EPA by states or tribes.

In EPA’s designations guidance for the 2008 ozone NAAQS, EPA recommended examining 

CSA/CBSAs because certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

using in this technical analysis to determine if a nearby area is contributing to a violation of the 2008 

ozone NAAQS. Congress required a similar approach in 1990 for areas classified as serious or above 

for the 1-hour ozone standard and EPA used the same basic approach in the designation process for the 

1997 ozone NAAQS. Where a violating monitor is not located in a CSA or CBSA, EPA’s guidance 

recommended using the boundary of the county containing the violating monitor as the starting point for 

considering the nonattainment area’s boundary. Phoenix-Mesa-Glendale is defined by the Office of

Management and Budget (OMB) as a metropolitan statistical area (MSA) and is composed solely of 

Maricopa and Pinal counties. The Phoenix-Mesa-Glendale MSA is not part of a larger CSA or CBSA. 

 4 The December 4, 2008 guidance memorandum “Area Designations for the 2008 Revised Ozone National Ambient Air 

Quality Standards” refers to 9 factors. In this technical support document we have grouped the emissions-related factors 

together under the heading of “Emissions and Emissions-Related Data,” which results in 5 categories of factors. 5 Lists of CBSAs and CSAs and their geographic components are provided at 

www.census.gov/population/www/metroareas/metrodef.html . The lists are periodically updated by the Office of 

Management and Budget. EPA used the most recent update, based on 2008 population estimates, issued on December 1, 

2009 (OMB Bulletin No. 10-02).
Technical Support Document for the State of Arizona - Page 3 of 21

Technical Support Document for 2008 Ozone NAAQS Designations

Arizona

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

Technical Analysis for Phoenix-Mesa

Figure 1 is a map of the existing Phoenix-Mesa, AZ nonattainment area. The map provides other 

relevant information including the locations and design values of air quality monitors, county names and 

boundaries, and indicates EPA’s 2008 ozone NAAQS nonattainment designation. Also shown is the 

boundary of the existing area that is designated nonattainment. See Map 1 in Appendix 1 (also included 

in Factor 1 below) for a detailed map of the partial county boundaries that EPA is using for the 

nonattainment area boundary.

Figure 1

For purposes of the 1997 8-hour ozone NAAQS, portions of Maricopa and Pinal Counties were 

designated nonattainment. Pinal County was not included in the nonattainment area for the 1-hour 

ozone NAAQS. However, for the 1997 8-hour ozone NAAQS, EPA designated an area that included 

the 1-hour nonattainment area and added Apache Junction, a portion of Pinal County. This small city 

was part of the Phoenix PM10 (particulate matter greater than 10 micrometers) nonattainment area. The

Apache Junction portion of Pinal County was added to the Phoenix 1997 8-hour ozone nonattainment 

area partly because of its PM10 nonattainment status, and partly because its population is associated with 

the greater Phoenix metropolitan area. 
Technical Support Document for the State of Arizona - Page 4 of 21

In March 2009, Arizona recommended that the same two partial counties, Maricopa and Pinal, be 

designated as “nonattainment” for the 2008 ozone NAAQS based on air quality data from 2006-2008, 

and additionally recommended extending the nonattainment boundaries at two locations in Maricopa 

County, and one location in Pinal County (letter from Janice Brewer, Governor, State of Arizona, to 

Laura Yoshii, Acting Regional Administrator, U.S. EPA Region IX, March 12, 2009 (hereafter, “ADEQ 

2009 Recommendations”)). ADEQ updated its 2009 recommendation on December 1, 2011 based on 

air quality data from 2008-2010 and preliminary data for 2009-2011. In its updated recommendation, 

the State continued to recommend extending the nonattainment boundary in two locations in Maricopa 

County, but withdrew its previous recommendation to extend the nonattainment boundary in Pinal 

County (letter from Henry R. Darwin, Director, Arizona Department of Environmental Quality, to Jared 

Blumenfeld, Regional Administrator, U.S. EPA Region IX, December 1, 2011 (hereafter, “ADEQ 2011 

Recommendations”)). The 2009 and 2011 recommendations are based on data from Federal Equivalent 

Method (FEM) monitors sited and operated in accordance with 40 CFR Part 58.

In March 2009, the Gila River Indian Community of the Gila River Indian Reservation recommended 

that reservation lands in Maricopa and Pinal counties be designated as “attainment” for the 2008 ozone 

NAAQS (letter from William Rhodes, Governor, Gila River Indian Community of the Gila River 

Reservation, to Laura Yoshii, Acting Regional Administrator, U.S. EPA Region IX, March 11, 2009).

In March 2009, the Salt River Pima-Maricopa Indian Community of the Salt River Reservation

recommended that reservation lands in Maricopa County be designated as “attainment/unclassifiable” 

for the 2008 ozone NAAQS (letter from Martin Harvier, Vice President, Salt River Pima-Maricopa 

Indian Community of the Salt River Reservation, to Laura Yoshii, Acting Regional Administrator, U.S. 

EPA Region IX, March 9, 2009).

In March 2009, the Tohono O’odham Nation of Arizona recommended that reservation lands in 

Maricopa, Pinal, and Pima counties be designated as “attainment/unclassifiable” for the 2008 ozone 

NAAQS (letter from Ned Norris, Chairman, Tohono O’odham Nation of Arizona, to Laura Yoshii, 

Acting Regional Administrator, U.S. EPA Region IX, March 11, 2009).

After considering these recommendations and based on EPA's technical analysis described below, EPA 

is designating two partial counties in Arizona and areas of Indian country (identified in Table 1 below) 

as “nonattainment” for the 2008 ozone NAAQS as the Phoenix-Mesa multi-jurisdictional nonattainment 

area. 
Technical Support Document for the State of Arizona - Page 5 of 21

Table 1. State’s and Tribe’s Recommended and EPA’s 2008 ozone NAAQS Nonattainment Counties or

Areas of Indian country for Phoenix-Mesa.

Phoenix-Mesa, AZ

State and Tribe’s 

Recommended Nonattainment 

Counties or Areas of Indian 

country

EPA’s

Nonattainment Counties or 

Areas of Indian country

Maricopa County Maricopa County (p) Maricopa County (p) 

Pinal County Pinal County (p) Pinal County (p)

Fort McDowell Yavapai 

Nation N/A Fort McDowell Yavapai Nation 

Salt River Pima-Maricopa 

Indian Community of the 

Salt River Reservation

Attainment/unclassifiable

Salt River Pima-Maricopa 

Indian Community of the Salt 

River Reservation

Tohono O'odham Nation of 

Arizona1 Attainment/unclassifiable Tohono O'odham Nation of 

Arizona (p)

p = partial

N/A = Tribe did not submit a recommendation.

EPA modifications to state or tribe recommendations are shown in bold.

1 The Tohono O’odham Nation of Arizona (Tohono O’odham) has non-contiguous land in the PhoenixMesa nonattainment area, in the unclassifiable/attainment area portions of Pinal County and the 

unclassifiable/attainment area of Pima County. Non-contiguous lands of Tohono O’odham are being

designated with the surrounding areas. This technical analysis addresses only those areas of Indian 

country within the Phoenix-Mesa 2008 ozone NAAQS nonattainment area.

Factor Assessment

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values for air quality monitors in counties in the 

existing 1997 8-hour ozone Phoenix-Mesa nonattainment area, based on data from the 2008-2010 period

(i.e., the 2010 design value, or DV), which are the most recent years with fully-certified air quality data. 

A monitor’s DV is the metric or statistic that indicates whether that monitor attains a specified air 

quality standard. The 2008 ozone NAAQS are met at a monitor when the annual fourth-highest daily 

maximum 8-hour average concentration, averaged over 3 years, is 0.075 parts per million (ppm) (75 

parts per billion (ppb)) or less. A DV is only valid if minimum data completeness criteria are met. See 

40 CFR part 50 Appendix P. Where several monitors are located in a county (or a designated 

nonattainment area or maintenance area), the DV for the county or area is determined by the monitor 

with the highest level.

[Note: Monitors that are eligible for providing design value data generally include State and Local Air 

Monitoring Stations (SLAMS) that are sited in accordance with 40 CFR Part 58, Appendix D (Section 

4.1) and operating with a federal reference method (FRM) or federal equivalent method (FEM) monitor 

that meets the requirements of 40 CFR part 58, Appendix A. All data from a special purpose monitor

(SPM) using an FRM or FEM which has operated for more than 24 months is eligible for comparison to 

the NAAQS unless the monitoring agency demonstrates that the data came from a particular period 

during which the requirements of Appendix A (quality assurance requirements) or Appendix E (probe 

and monitoring path siting criteria) were not met.]
Technical Support Document for the State of Arizona - Page 6 of 21

The existing Phoenix-Mesa nonattainment area for the 1997 ozone NAAQS comprises the central 

portion of Maricopa County and a small portion of northern Pinal County (see Map 1a in Appendix 2). 

The 2010 DVs for the ozone NAAQS for counties in the existing Phoenix-Mesa nonattainment area are 

shown in Table 2. 

Table 2. Air Quality Data.

County State Recommended Nonattainment? 2008-2010 Design Value (ppb)

Maricopa, AZ Yes (partial) 77

Pinal, AZ Yes (partial) 74

Ozone monitors relevant for comparison to the NAAQS and information from additional data sources 

within the existing Phoenix-Mesa nonattainment area and the surrounding area are shown in Appendix 

1, Map 1 (also inserted below). Arizona’s ozone season encompasses the entire year, but some ozone 

monitors in the existing Phoenix-Mesa nonattainment area have been approved to operate on a seasonal 

schedule per 40 CFR part 58, Appendix D, section 4.1(i). Certified, quality assured data are available in 

EPA’s Air Quality System (AQS) for all areas through calendar year 2010. The Appendix 1 map 

includes preliminary 2011 DVs for the existing Phoenix-Mesa nonattainment area for informational 

purposes only. For each monitor, Appendix 1 lists the monitor, the 2008-2010 DV (certified and quality 

assured in AQS) and the preliminary 2009-2011 DV (data that are not yet certified and quality assured 

in AQS are denoted with an underline). Absence of a DV is symbolized with an “x”.

Appendix 3 lists the DVs for monitors in the existing Phoenix-Mesa nonattainment area. Monitors 

shown in bold are the DV monitors (i.e., the monitor with the highest DV) for each individual county. 

Monitors shown in red font are the DV monitor for the nonattainment area. Values with an asterisk do 

not meet data completeness, and therefore those DVs are not relevant for comparison to the NAAQS and 

are solely provided for informational purposes.
Technical Support Document for the State of Arizona - Page 7 of 21

From Appendix 1, Map 1: For map legend describing monitors, emissions, traffic, population, and boundaries, see Appendix 1.
Technical Support Document for the State of Arizona - Page 8 of 21

Monitors in Maricopa County show a violation of the 2008 8-hour ozone standard based on 2008-2010 

data. These violating monitors are located within the portion of Maricopa County that was included as 

part of the designated nonattainment area for the 1997 ozone standard. Since the County contains 

violating monitors, Factor 1 supports including Maricopa County, in whole or in part, in the PhoenixMesa nonattainment area. A county (or partial county) must also be designated nonattainment if it 

contributes to a violation in a nearby area. Each county without a violating monitor that is located near a 

county with a violating monitor has been evaluated based on the weight of evidence of the five factors 

and other relevant information to determine whether it contributes to the nearby violation (see Factor 2 

discussion, below). In addition, we evaluate those factors to determine whether to include all of 

Maricopa County or just a part within the designated nonattainment area.

Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions of ozone precursors, nitrogen oxides (NOx) and volatile organic compounds

(VOC), and other emissions-related data that provide information on areas contributing to violating 

monitors.

Emissions data

EPA evaluated county-level emission data for NOx and VOC derived from the 2008 National Emissions 

Inventory (NEI), version 1.5. This is the most recently available NEI (see 

http://www.epa.gov/ttn/chief/net/2008inventory.html). Emissions in a nearby area indicate the potential 

for the area to contribute to observed violations. Table 3 shows emissions of NOx and VOC (given in 

tons per year) for Maricopa and Pinal counties. 

Table 3. Total 2008 NOx and VOC Emissions.

County State Recommended

Nonattainment? NOx (tpy) VOC (tpy)

Maricopa, AZ Yes (partial) 89,020 90,615 

Pinal, AZ Yes (partial) 11,668 11,531 

Areawide: 100,688 102,146 

Maricopa and Pinal counties, with an area of approximately 9,200 square miles and 5,366 square miles, 

respectively, are among the largest counties in the nation, and, aside from the urban core, are composed 

entirely of desert terrain. Emissions of ozone precursors shown in Table 2 represent emissions from the 

entire counties of Maricopa and Pinal, not just the portions of those counties recommended by the State 

for inclusion in the Phoenix-Mesa nonattainment area. Emissions of NOx and VOC from Maricopa 

County are nearly eight times larger than NOx and VOC emissions from Pinal County. Most of the 

stationary source emissions of ozone precursors are located in the center of the State-recommended

nonattainment area (see Map 1 of Appendix 1), with additional stationary sources scattered in the 

western portion of the State-recommended nonattainment area of Maricopa County, and fewer stationary 

sources in the eastern and northern portions of the State-recommended nonattainment area of Maricopa 

County. Additional stationary sources are located in the small section of Pinal County that is included in 

the existing Phoenix-Mesa 1997 ozone nonattainment area. Numerous stationary sources are located in 

Pinal County outside of EPA’s boundary for the 2008 ozone NAAQS Phoenix-Mesa nonattainment area, 

but are widely scattered and generally located near roadways. In 2009, the State recommended 

expanding the existing ozone nonattainment area in the southwest portion of the area, in order to include

the Gila River Power Station (see Map 1 of Appendix 1). Additionally, the State recommended 

extending the western boundary of the nonattainment area farther west into Maricopa County by 5 - 10 
Technical Support Document for the State of Arizona - Page 9 of 21

miles. This expansion incorporates a small (less than 100 tpy) power plant. In its updated 

recommendation submitted to EPA on December 1, 2011, the State continued to recommend extending 

the nonattainment boundary to incorporate these two areas of Maricopa County. 

In 2009, the State had also recommended that the existing 1997 ozone nonattainment boundary be 

extended to the southeast to incorporate a larger portion of Pinal County. In 2011, the State’s updated 

recommendation excluded this area. Several small (less than 15 tpy of NOx or VOC) stationary sources 

of ozone precursor emissions are located in this area of Pinal County (see Map 1 of Appendix 1). These 

sources are more widely distributed geographically compared to the small portion of Pinal County that is 

part of the existing 1997 ozone nonattainment area.

In its February 2009 redesignation request and maintenance plan for the 1997 8-hour ozone NAAQS, the 

State provided information on the proportion of point source emissions from the entire county of

Maricopa County compared to the those from the existing (for the 1997 ozone NAAQS) ozone 

nonattainment area6. Based on its 2005 periodic emission inventory, the State determined that the 

existing ozone nonattainment area, composed of portions of Maricopa and Pinal counties, captured the 

majority of point sources of emissions from Maricopa County – the county that contributes dominantly 

to total emissions from Maricopa and Pinal counties (see Table 3). For 2005, the existing ozone 

nonattainment area represented 99% of VOC emissions from Maricopa County, and nearly 87% of NOx

emissions from Maricopa County. The State’s recommendation to expand the Maricopa County portion 

of the nonattainment area to encompass new sources of ozone precursor emissions to the west and 

southwest of the existing nonattainment area should continue to ensure that relevant emissions sources 

are included in the nonattainment area designation. 

Population density and degree of urbanization

EPA evaluated the population and vehicle use characteristics and trends of the area as indicators of the 

probable location and magnitude of non-point source emissions. These include ozone-creating 

emissions from on-road and off-road vehicles and engines, consumer products, residential fuel 

combustion, and consumer services. Areas of dense population or commercial development are an 

indicator of area source and mobile source NOx and VOC emissions, which contribute to ozone 

formation. Rapid population or growth in vehicle miles traveled (VMT) (see below) in a county on the 

urban perimeter signifies increasing integration with the core urban area, and indicates that it may be 

appropriate to include the area associated with area source and mobile source emissions as part of the 

nonattainment area. Table 4 shows the population, population density, and population growth 

information for Maricopa and Pinal counties.

 6 See March 23, 2009 submittal of the 8-hour ozone redesignation request and maintenance plan for the Maricopa 

nonattainment area from Patrick Cunningham, Acting Director, ADEQ to Laura Yoshii, Acting Regional Administrator, EPA 

Region IX. The maintenance plan and redesignation request are available from the Maricopa Association of Governments at: 

http://www.azmag.gov/Projects/Project.asp?CMSID2=1120&MID=Environmental%20Programs
Technical Support Document for the State of Arizona - Page 10 of 21

Table 4. Population and Growth.

County

State 

Recommended 

Nonattainment?

2010 Population

2010 Population 

Density

(1000 pop/sq mi)

Absolute change

in population

(2000-2010)

Population % 

change

(2000-2010)

Maricopa, AZ Yes (partial) 3,817,117 0.41 719,617 +23% 

Pinal, AZ Yes (partial) 375,770 0.07 194,494 +107% 

Areawide: 4,192,887 0.29 914,111 +28%

Sources: U.S. Census Bureau population estimates for 2010 as of August 4, 2011 

(http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=DEC_10_PL_GCTPL2.STO5&prodType

=table)

Population information shown in Table 4 represents all of Maricopa and Pinal counties, not just the 

portions of those counties recommended by the State for inclusion in the 2008 ozone Phoenix-Mesa 

nonattainment area. Similar to the stationary source emissions of ozone precursors, the population of 

Maricopa County is substantially larger and denser than Pinal County. Although the percent change in 

population over 2000-2010 in Pinal County was very large (107%), its absolute change in population 

was still much smaller than Maricopa County’s – less than a third. The largest population centers are 

located in Maricopa County (see Map 1a in Appendix 2). The eastern portion of the Phoenix 

metropolitan area extends into the Apache Junction portion of Pinal County and is included in the 

existing nonattainment area, as well as the State’s recommended nonattainment area. Aside from the 

urbanized Phoenix area, the rest of both Maricopa and Pinal counties are sparsely populated. The 

portion of Pinal County, which was included in the State’s 2009 recommendation but excluded in the 

2011 recommendation, contains a few population centers, but is generally more sparsely populated 

compared to Apache Junction, the portion of Pinal County that is part of the existing 1997 ozone 

nonattainment area.

In its February 2009 redesignation request and maintenance plan for the 1997 8-hour ozone NAAQS, the 

State also provided information on populations within the existing 1997 ozone nonattainment area and 

Maricopa County – the county that contributes dominantly to total emissions from Maricopa and Pinal 

counties. Based on 2004 demographic data, the resident and non-resident populations within the 

existing ozone nonattainment area were 100.52% and 109.09% of the resident and non-resident

populations of Maricopa County, respectively. Therefore, in 2004, the population of the existing 1997 

ozone nonattainment area (consisting of portions of Maricopa and Pinal counties) was greater than the 

population of Maricopa County. 

Traffic (VMT) data

EPA evaluated the commuting patterns of residents in the area, as well as the total VMT for each 

county. In combination with the population/population density data and the location of main 

transportation arteries (see above), this information helps identify the probable location of non-point 

source emissions. A county with high VMT is generally an integral part of an urban area and indicates 

the presence of motor vehicle emissions that may contribute to ozone formation and nonattainment in 

the area. Rapid population or VMT growth in a county on the urban perimeter signifies increasing 

integration with the core urban area, and indicates that the associated area source and mobile source 

emissions may be appropriate to include in the nonattainment area. Table 5 shows total 2008 VMT for 

Maricopa and Pinal counties.
Technical Support Document for the State of Arizona - Page 11 of 21

Table 5. Traffic (VMT) data.

County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

Maricopa, AZ Yes (partial) 33,393 

Pinal, AZ Yes (partial) 3,972 

Areawide: 37,365 

*MOBILE model VMTs are those inputs into the NEI version 1.5. 

The total 2008 VMT in Maricopa County was over eight times higher than the 2008 VMT in Pinal 

County. The highest non-truck traffic volume occurs within the population centers located in the 

Maricopa County portion of the nonattainment area, with some heavy traffic on roads that run south, 

north, and to a lesser extent, west from the population centers (see Map 1 of Appendix 1). 

Factor 3: Meteorology (weather/transport patterns)

EPA evaluated available meteorological data to help determine how meteorological conditions, such as 

weather, transport patterns and stagnation conditions would affect the fate and transport of precursor 

emissions contributing to ozone formation.

Maricopa and Pinal counties lie in a hot desert area of Arizona, where summer temperatures regularly 

exceed 100 degrees F. In the absence of the strong winds associated with summer storms that 

sometimes occur in the area, the high temperatures are conducive to ozone formation. ADEQ has 

described the basic flow pattern that results in “sloshing” of pollutant towards the west, and then later in 

the day back toward the east:

“The mountain-valley flow defines the daily surface wind patterns in the Phoenix area in the 

absence of synoptic weather systems with associated cold fronts. As a result, Phoenix has a 

typical diurnal wind pattern that exists nearly year-round due to its geographical position within 

the valley. ... When the sun rises over the Superstitions in the east, the east-facing mountains in 

the west valley such as the White Tank Mountains begin to heat up. As the morning progresses, 

an energy imbalance is created where the warmer air over the White Tank Mountains rises while 

the cooler air over the east mountains such as the Superstition mountains sinks. This causes the 

surface winds across the valley to move from east to west.... By about 2 p.m., the mountains in 

the east part of the valley have more direct sunlight than the west. This imbalance in energy leads 

to a shift in surface winds from out of the west during the afternoon period. As the sun goes 

down, equal cooling takes place and winds decrease to nearly calm.”7

While the mountains to east and west provide partial barriers to transport of pollutants in certain 

directions (especially the northeast), they do not form a closed basin. There is opportunity for emissions 

from outside the immediate metropolitan Phoenix area to contribute to ozone formation. “Wind patterns 

in Phoenix suggest that ozone and ozone precursors can be transported in the morning from the far west 

and southern portions of the valley and impact monitors in the Phoenix valley.”8 In recognition of this, 

the State recommended extending the boundaries of the previous ozone nonattainment area. The 

recommendation included several new point sources to the west and southwest, as discussed above 

under Factor 2. 

 7 ADEQ 2009 Recommendations, p.44-45 8 ADEQ 2009 Recommendations, p.42
Technical Support Document for the State of Arizona - Page 12 of 21

Figure 2

Source: ADEQ 2009 Recommendations, p.54 Figure III.36: “High mountain slopes to the 

west of Phoenix are heated in the morning and surface air is drawn towards the west.”

Figure 3

Source: ADEQ 2009 Recommendations, p.54 Figure III.37: “High mountain slopes to the 

east of Phoenix are heated in the late afternoon and surface air is drawn towards the east.”

The west-east flow pattern is generally consistent with the 30-year average of National Weather Service

summer wind direction frequencies computed by EPA, as shown in the “radar”-style wind rose diagram 

below (Figure 4).
Technical Support Document for the State of Arizona - Page 13 of 21

Figure 4

Factor 4: Geography/topography (mountain ranges or other air basin boundaries)

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

airshed and, therefore, the distribution of ozone over the area.

The Phoenix-Mesa area is partly surrounded by mountains of varying heights. As described by the 

State:

“The Phoenix metropolitan area lies in a valley bordered by the Superstition Mountains 

to the east, the New River Mountains to the north and northeast, the Hieroglyphic 

Mountains to the northwest near Lake Pleasant, the White Tank Mountains in the west, 

the Estrella Mountains to the southwest, and the South Mountains to the south. The Salt 

River runs through the southern part of the metropolitan area and exits to the southwest 

with the Gila and Agua Fria Rivers joining it near Goodyear, and the Hassayampa River 

joining west of Palo Verde.”9

While the mountains to the east and west provide partial barriers to transport of pollutants in certain 

directions (especially the northeast), they do not form a closed basin. There is opportunity for emissions 

from outside the immediate metropolitan Phoenix area to contribute to ozone formation. “Wind patterns 

in Phoenix suggest that ozone and ozone precursors can be transported in the morning from the far west 

 9 ADEQ 2009 Recommendations, p.44
Technical Support Document for the State of Arizona - Page 14 of 21

and southern portions of the valley and impact monitors in the Phoenix valley.”10 In recognition of this, 

the State recommended a nonattainment area which incorporates source areas that are relatively far from 

central metropolitan Phoenix and the highest ozone concentrations.

Factor 5: Jurisdictional boundaries

For each potential nonattainment area, we considered existing jurisdictional boundaries to provide a 

clearly defined legal boundary and to help identify the areas appropriate for carrying out the air quality 

planning and enforcement functions for nonattainment areas. Examples of jurisdictional boundaries 

include existing/prior nonattainment area boundaries for ozone or other urban-scale pollutants, county 

lines, air district boundaries, township boundaries, areas covered by a metropolitan planning 

organization, state lines, areas of Indian country, and urban growth boundaries. Where existing 

jurisdictional boundaries were not adequate or appropriate to describe the nonattainment area, other 

clearly defined and permanent landmarks or geographic coordinates were considered.

The Phoenix-Mesa nonattainment area has previously established nonattainment boundaries associated 

with both the 1-hour and 1997 8-hour ozone NAAQS. The boundary of the Phoenix-Mesa

nonattainment area for the 1997 ozone NAAQS includes a large portion of Maricopa County and a small 

portion of Pinal County (Apache Junction). The State has recommended a slightly different boundary 

for the 2008 ozone NAAQS. The State has requested that EPA expand the boundary of the 

nonattainment area for the 2008 ozone NAAQS, relative to the boundary established for the 1997 ozone 

NAAQS. 

The Phoenix-Mesa-Glendale metropolitan statistical area (MSA) is composed solely of Maricopa and 

Pinal counties. The Phoenix-Mesa-Glendale MSA is not part of a combined statistical area (CSA). The 

majority of the urban area lies mainly in Maricopa County, with a portion of the eastern urbanized area 

extending into Pinal County. The Maricopa Association of Governments (MAG), a metropolitan 

planning organization (MPO), has jurisdiction of both air and transportation planning for the 

metropolitan area. Together, Maricopa and Pinal counties comprise the Phoenix-Mesa-Glendale 

Metropolitan Statistical Area.

11 The cities of Phoenix, Mesa and Glendale are entirely contained within 

Maricopa County. But, as noted above, the urbanized area extends into Pinal County.

The Maricopa County partial county boundary, for both the recommended area and the existing 

nonattainment area for the 1997 ozone NAAQS, follows the county boundary to the north, east and 

southeast (excluding Gila River Indian Community, see discussion below, and including a small portion 

of Pinal County that bounds the eastern edge of the Phoenix-Mesa urbanized area). The boundaries for 

this area are consistent with MAG’s north, east, and southeast planning area boundaries. To the west 

and southwest, the ozone nonattainment area boundary follows township and range boundaries in a way 

that encompasses stationary and mobile sources and population centers. MAG defined an “Area A” for 

air pollution control purposes in the past, mainly associated with dust controls and other restrictions 

(e.g., no-burn days). Area A became part of the 1-hour ozone as well as the 1997 8-hour ozone 

nonattainment area. Area A is bounded to the west by township and range boundaries. For the western 

and southwestern boundaries for the designated Phoenix-Mesa nonattainment area for the 2008 ozone 

NAAQS, the State recommended including the entire existing area and two expanded areas in the east 

and south. This includes all of Area A, several township and ranges on the west that were included in 

 10 ADEQ 2009 Recommendations, p.42 11 The Office of Management and Budget names such areas in decreasing ranking of populated areas within the MSA. 

Phoenix is therefore larger than Mesa, which is larger than Glendale.
Technical Support Document for the State of Arizona - Page 15 of 21

prior ozone designations (for 1-hour and the 1997 8-hour ozone NAAQS), and several newly added 

township and range areas to the west and to the southwest. The State recommended these expanded 

boundaries because there are several large stationary sources located in those areas (e.g., power plants).

In 2009, the State recommended expanding the Pinal County portion of the existing ozone boundary to 

encompass a violating monitor and a planned power plant. However, on December 1, 2011, in an

update to its 2009 recommendation, the State reverted to the existing Pinal partial county boundary, 

which includes only the Apache Junction portion. The State explained that more recent air quality 

monitoring in the formerly recommended area shows the previously violating monitor is now attaining 

the standard. In addition, economic conditions put the development of a power plant in the area in 

doubt. 

The Phoenix-Mesa nonattainment area also includes an area of Indian country. As defined at 18 U.S.C. 

1151, “Indian country” 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.” EPA recognizes the sovereignty 

of tribal governments, and has attempted to take the desires of the tribes into account in establishing 

appropriate nonattainment area boundaries.

Evaluation of Recommendation from Gila River Indian Community of the Gila River 

Indian Reservation

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

areas that violate the NAAQS and those areas that contribute to violations. EPA has evaluated 

the recommendation of the Gila River Indian Community of the Gila River Indian Reservation

(Gila River) based on currently available information. 

In 2004, EPA established the Phoenix-Mesa nonattainment area boundaries for the 1997 ozone 

NAAQS that excluded the portions of Maricopa and Pinal counties that encompass the Gila 

River.

In March 2009, Gila River recommended that portions of Gila River in Maricopa and Pinal 

counties be designated as “attainment” for the 2008 ozone NAAQS (letter from William Rhodes, 

Governor, Gila River Indian Community, to Laura Yoshii, Acting Regional Administrator, U.S. 

EPA Region IX, March 11, 2009).

Gila River is a federally recognized tribe with reservation lands in Maricopa and Pinal counties. 

The majority of the Indian country is located in Pinal County and has not been subject to 

urbanization and is mainly a rural environment with two main population centers in St. Johns and 

Sacaton and over 35,000 acres of agricultural lands. Gila River has an on-reservation population 

of approximately 22, 000 people. These population centers are not integrated within the Phoenix 

metropolitan area and pale in comparison to the 3,800,000 people living in the adjacent Maricopa 

County. Also, The South Mountains to the north and the Estrella Mountains in the west may 

provide some geographical and topographic barriers between the Phoenix-Mesa nonattainment 

area and the majority of Gila River reservation lands. These areas of Indian country and the 

adjacent Phoenix-Mesa nonattainment areas are shown in Map 1a in Appendix 2. 
Technical Support Document for the State of Arizona - Page 16 of 21

Currently, Gila River operates a network of two ozone monitors within the tribal boundaries that 

represent both the northwestern and the central portions of the Gila River lands. The map in 

Appendix 1 shows monitor locations for the Phoenix-Mesa nonattainment area, including Gila 

River monitors. EPA anticipates relying on 2008-2010 data to designate this area. Appendix 1 

provides preliminary 2011 data for informational purposes only. Based on the information 

currently available, both monitors operated by Gila River in their area of Indian country indicate 

that the area is attaining the 2008 ozone NAAQS for 2008-2010.

Because monitors located in Gila River’s area of Indian country indicate the area is attaining the 

2008 ozone NAAQS, based on the low population, the largely rural environment, and the 

presence of some topographical barriers that separate Gila River from the adjacent nonattainment 

area, EPA continues to agree that that Gila River’s area of Indian country has different ozone 

concentrations than surrounding areas and is not affected by the poor air quality present in the 

Phoenix-Mesa nonattainment area. Therefore, consistent with the EPA Tribal Designations 

Policy, EPA is designating the Gila River Indian Community of the Gila River Indian 

Reservation unclassifiable/attainment for the 2008 ozone NAAQS, consistent with the 

designation of the adjacent areas in Pinal County.

Evaluation of Recommendation from Tohono O’odham Nation of Arizona

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

areas that violate the NAAQS and those areas that contribute to violations. EPA has evaluated 

the recommendation of the Tohono O'odham Nation of Arizona (Tohono O’odham) based on 

currently available information. 

In 2004, EPA established the Phoenix-Mesa nonattainment area boundaries for the 1997 ozone 

NAAQS. This nonattainment area included the portion of Maricopa County that encompassed

the non-contiguous lands of Tohono O’odham, however, this land was not taken into trust for the 

Tribe by the Department of Interior until 201012, and was therefore not considered to be an area 

of Indian country until that time.

In March 2009, Tohono O’odham recommended that the portions of Tohono O’odham in 

Maricopa, Pinal, and Pima counties be designated as “attainment/unclassifiable” for the 2008 

ozone NAAQS (letter from Ned Norris, Chairman, Tohono O’odham Nation, to Laura Yoshii, 

Acting Regional Administrator, U.S. EPA Region IX, March 11, 2009).

EPA has included a portion of Tohono O'odham lands located in Maricopa County (specifically, 

areas of Indian country located near Glendale, Arizona) as part of the Phoenix-Mesa 

nonattainment area. Tohono O’odham’s remaining Indian country in Maricopa, Pinal and Pima 

 12 On June 23, 2010 the U.S. Department of Interior (DOI) approved a request from the Tohono O'odham Nation to take 

53.54 acres of land held in fee by the Tribe and located in Maricopa County, AZ near Glendale, into trust (75 FR 21130).

DOI made this approval pursuant to the Gila Bend Indian Reservation Lands Replacement Act, P.L. 99-503, Stat 100 1798 

(1986), Section 6(d), which mandates the following: "Any land which the Department of Interior holds in trust for the Tribe 

shall be deemed to be a Federal Indian Reservation for all purposes." EPA is designating this trust land along with the 

surrounding Phoenix-Mesa nonattainment area. EPA notes that it is not making any determination on the Tribe's Reservation

boundary through this designation process.
Technical Support Document for the State of Arizona - Page 17 of 21

counties are not contiguous and EPA is designating these lands as “unclassifiable/attainment”,

consistent with the designation of the surrounding area. 

Air Quality Data

Currently, Tohono O’odham does not operate any air quality monitors. However, monitors near 

the Tribe’s area of Indian country near Glendale in Maricopa County show a violation of the 

2008 8-hour ozone standard based on 2008-2010 data. Map 1 in Appendix 1 shows monitor 

locations for the Phoenix-Mesa nonattainment area. For each monitor, Appendix 1 lists the 

monitor, the 2008-2010 DV (certified and quality assured in AQS) and the 2009-2011 DV (data 

that are not yet certified and quality assured in AQS are denoted with an underline).

Based on the lack of topographic barriers, similarities in meteorology and transport patterns to 

the surrounding area, Tohono O’odham’s Indian country near Glendale is expected to have 

similar air quality as the surrounding area.

Emissions and Emissions-Related Data

The lands of Tohono O’odham near Glendale consist of 53.54 acres of reservation lands. EPA is 

not aware of any sources of ozone precursor emissions within this area of Indian country. 

Information on emissions, population density and degree of urbanization, traffic and commuting 

patterns for the Phoenix area can be found in Factor 2 of the Phoenix-Mesa nonattainment area 

technical analysis, above. 

Meteorology (Weather/Transport Patterns)

Tohono O’odham’s Indian country near Glendale is located in central Maricopa County and 

experiences similar meteorology and transport patterns as the Phoenix metropolitan area. 

Therefore, the information for the Phoenix-Mesa nonattainment area discussed in Factor 3 above, 

also characterizes the meteorology and transport patterns for this part of Tohono O’odham. 

Geography/Topography

Tohono O’odham’s Indian country near Glendale does not have any geographical or 

topographical barriers that would prevent air pollution transport from the surrounding PhoenixMesa nonattainment area. Therefore, geography and topography support including this portion 

of Tohono O’odham with the surrounding area.

Jurisdictional Boundaries

Tohono O'odham is a federally recognized tribe with non-contiguous reservation land in 

Maricopa, Pinal, and Pima counties. These areas of Indian country and the surrounding 

nonattainment areas are shown on Map 1a in Appendix 2. The majority of the Tribe’s 

reservation lands are located in Pinal and Pima counties, outside of the Phoenix-Mesa 

nonattainment area. However, the 53.54 acres of Indian country taken into trust by the U.S. 

Department of Interior for the Tribe in 2010 are located near Glendale, Arizona, which is about 

nine miles northwest of downtown Phoenix and near the center of the Phoenix-Mesa 

nonattainment area. There are no geographic or topographical barriers that preclude air pollution 

transport from the surrounding Phoenix-Mesa nonattainment area.
Technical Support Document for the State of Arizona - Page 18 of 21

Conclusion for Tohono O’odham

Based upon currently available information, it appears that Tohono O’odham’s area of Indian 

country near Glendale, AZ is affected by the poor air quality that exists within the Phoenix-Mesa 

nonattainment area. Therefore, while the Tribe has recommended its areas of Indian country be 

designated “attainment/unclassifiable”, consistent with the EPA Tribal Designations Policy, EPA 

is including a portion of Tohono O'odham lands located in Maricopa County (specifically, areas 

of Indian country located near Glendale, Arizona) as part of the Phoenix-Mesa nonattainment 

area. The remaining lands located in Maricopa, Pinal and Pima counties are not contiguous and 

EPA is designating these lands as unclassifiable/attainment, consistent with the designation of 

the surrounding area. 

Evaluation of Recommendation from Salt River Pima-Maricopa Indian Community of 

the Salt River Reservation

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

areas that violate the NAAQS and those areas that contribute to violations. EPA has evaluated 

the recommendation of the Salt River Pima-Maricopa Indian Community of the Salt River 

Reservation (Salt River) based on currently available information. 

In 2004, EPA established the Phoenix-Mesa nonattainment area boundaries for the 1997 ozone

NAAQS that included portions of Maricopa County that encompass Salt River. 

In March 2009, the Salt River Pima-Maricopa Indian Community recommended that portions of 

Salt River in Maricopa County be designated as “attainment/unclassifiable” for the 2008 ozone 

NAAQS (letter from Martin Harvier, Vice President, Salt River Pima-Maricopa Indian 

Community, to Laura Yoshii, Acting Regional Administrator, U.S. EPA Region IX, March 9, 

2009). Based on the factors discussed below, EPA has concluded that Salt River’s Indian 

country should be designated nonattainment as part of the Phoenix-Mesa nonattainment area for 

the 2008 ozone NAAQS. 

Air Quality Data

Currently, Salt River operates a network of four ozone monitors within its areas of Indian 

country. Map 1 in Appendix 1 shows monitor locations for the Phoenix-Mesa nonattainment 

area, including Salt River monitors. For each monitor, Appendix 1 lists the monitor, the 2008-

2010 design value (DV) and the preliminary 2009-2011 DV (data that are not yet certified and 

quality assured in AQS are denoted with an underline). Values with an asterisk do not meet data 

completeness, and therefore those DVs are not relevant for comparison to the NAAQS and are 

solely provided for informational purposes. Absence of a DV is indicated with an “x.” EPA is 

designating Arizona for the 2008 ozone NAAQS using certified 2008-2010 DV data; preliminary 

2011 data are provided for informational purposes.

Based on the information currently available, the Red Mountain ozone monitor (AQS ID: 

TT6157021; see Appendix 3) operated by Salt River on tribal lands has a 2008-2010 8-hour 

design value of 0.076 ppm, which constitutes a violation of the 2008 ozone NAAQS. 
Technical Support Document for the State of Arizona - Page 19 of 21

Emissions and Emissions-Related Data

Salt River consists of 54,000 acres of reservation lands, which is home to over 10,000 tribal 

members. Salt River has some emissions sources within its area of Indian country, including

aggregate mining facilities, asphalt and concrete batch plants, and landfills. Also, two major 

roadways, the Pima Loop 101 (Highway 101- Pima Freeway) and the Beeline Highway (Arizona 

Highway 87), pass through Salt River.

General information on emissions, population density and degree of urbanization, traffic and

commuting patterns for the Phoenix-Mesa nonattainment area can be found in the general 

Phoenix-Mesa nonattainment area Factor 2 discussion above and is applicable to Salt River. We 

do not have independent information solely for the Salt River reservation lands.

Meteorology (Weather/Transport Patterns)

Salt River is fairly integrated within the surrounding urban area and therefore the information for 

the Phoenix-Mesa nonattainment area discussed in Factor 3 also characterizes the meteorology 

and transport patterns for Salt River.

Geography/Topography

Salt River area does not have any geographical or topographical barriers that would prevent air 

pollution transport from the surrounding Phoenix-Mesa nonattainment area. Therefore, 

geography and topography support including Salt River’s Indian country with the surrounding 

area.

Jurisdictional Boundaries

Salt River is a federally recognized tribe located in the eastern portion of the Phoenix 

metropolitan area. Map 1a shows the locations and the area of Indian country within the 

Phoenix-Mesa nonattainment area.

Conclusion for Salt River

While Salt River has recommended an “attainment/unclassifiable” designation, based on the 

information currently available and the five factor analysis above, including a violating monitor 

located in Salt River’s area of Indian county and the presence of several sources of ozone 

precursor emissions, consistent with the EPA Tribal Designations Policy, EPA is designating

Salt River’s Indian country as part of the Phoenix-Mesa nonattainment area for the 2008 ozone 

NAAQS. 
Technical Support Document for the State of Arizona - Page 20 of 21

Conclusion

Based on the assessment of factors described above, EPA has concluded that the following counties and 

areas of Indian country should be included as part of the Phoenix-Mesa, AZ nonattainment area because 

they are either violating the 2008 ozone NAAQS or contributing to a violation in a nearby area: 

Maricopa County (partial), Pinal County (partial), the Fort McDowell Yavapai Nation (Fort McDowell), 

Salt River, and Tohono O’odham (partial).

Based on 2008-2010 DV data (Factor 1), Maricopa County contains two violating monitors and Pinal 

County does not contain any violating monitors. Consideration of only air quality data and the location 

of violating monitors indicate that all or part of Maricopa County should be included in the 2008 8-hour 

ozone nonattainment area.

Emissions of ozone precursors (Factor 2) from Maricopa County are over ten times larger than from 

Pinal County. The State’s partial boundary recommendations for Maricopa and Pinal Counties include

the dense population centers and roadways, as well as the majority of the stationary sources of ozone 

precursor emissions in Maricopa and Pinal counties. Maricopa and Pinal counties are geographically 

large. Outside of the densely populated urban Phoenix core, these counties are sparsely populated with 

relatively few stationary and mobile sources of ozone precursor emissions. The distribution of 

stationary and mobile emission sources (Factor 2) and information provided by the State in its 

redesignation request and maintenance plan for the 1997 8-hour ozone NAAQS – indicating that the 

majority of emissions in Maricopa County are well represented by the 1997 ozone nonattainment area –

supports the State’s recommendation to use the existing 1997 8-hour ozone nonattainment boundary

while also expanding the boundaries in Maricopa County to encompass additional stationary sources 

located to the west and southwest. Because Pinal County contributes a small fraction to total ozone 

precursor emissions from Maricopa and Pinal counties, and because stationary and mobile sources in 

Pinal County, outside the State-recommended nonattainment area, are widely distributed throughout the 

large county area, Factor 2 supports the State’s recommendation to maintain the existing 1997 8-hour 

ozone nonattainment boundary around the Apache Junction area.

Meteorology and weather or transport patterns (Factor 3) and geography and topography (Factor 4) 

show that there is the potential for some contribution to ozone violations from emissions occurring 

toward the southeast, in Pinal County. In considering jurisdictional boundaries (Factor 5), EPA notes 

that the State’s recommended nonattainment area boundaries expands the Maricopa County portion of 

the nonattainment area, but is otherwise consistent with the 1997 8-hour ozone nonattainment area. 

Based on our analysis of all five factors, EPA supports the State’s recommendation for the 

nonattainment area boundary in Maricopa and Pinal counties. 

Three tribes located within or near the boundaries of the Phoenix-Mesa nonattainment area submitted 

recommendations to EPA. EPA has concluded that Gila River’s Indian country, located in Maricopa 

and Pinal counties, should be excluded from the Phoenix-Mesa nonattainment area and designated 

unclassifiable/attainment based on air quality data, the low population, the largely rural environment, 

and the presence of some topographical barriers. Based upon currently available information, it appears 

that the portion of Tohono O'odham’s Indian country located in Maricopa County experiences similar

poor air quality as the Phoenix-Mesa nonattainment area. Therefore, EPA has concluded that the 

portions of Tohono O'odham located in Maricopa County (specifically, areas of Indian country located 

in Glendale, Arizona) should be included as part of the Phoenix-Mesa nonattainment area. Because the 

remaining portions of Tohono O’odham are non-contiguous and are not located within the Phoenix-
Technical Support Document for the State of Arizona - Page 21 of 21

Mesa nonattainment area for the 2008 ozone NAAQS, EPA is designating all other portions of Tohono 

O’odham located in Maricopa, Pinal, and Pima counties as “unclassifiable/attainment” consistent with 

the surrounding areas. EPA has also concluded that Salt River’s Indian country should be designated as 

“nonattainment” as part of the Phoenix-Mesa nonattainment area for the 2008 ozone NAAQS, due to a 

violating monitor on tribal lands and consideration of other factors discussed above. Fort McDowell did 

not submit a recommendation, and consistent with the EPA Tribal Designations Policy, EPA has 

concluded that Fort McDowell’s area of Indian country should be designated nonattainment as part of 

the Phoenix-Mesa nonattainment area for the 2008 ozone NAAQS.

Based on our consideration of all five factors, EPA concludes that Maricopa (partial) and Pinal (partial) 

counties in Arizona and areas of Indian country – Fort McDowell, Salt River, and Tohono O’odham 

(partial) – should be designated nonattainment for the 2008 ozone NAAQS as the Phoenix-Mesa, AZ

multi-jurisdictional nonattainment area. 
Appendix 1:

Map showing Monitors, Emissions, Vehicle Traffic, and General Population


Appendix 2:

Map showing Jurisdictional Boundaries and Detailed Population