1 

 

Technical Support Document for 

EPA’s Proposed Action on the 

State of Arizona’s 

2009 Infrastructure State Implementation Plan 

(Transport Portion) for the 

2006 24-hour Fine Particulate (PM2.5) 

National Ambient Air Quality Standard 

Air Division 

U.S. EPA Region 9 

July 2012 

 
2 

For information on this technical support document, please contact: 

Carol Bohnenkamp 

Office of Air Quality Assessment and Analysis 

U.S. Environmental Protection Agency – Region 9 

75 Hawthorne Street 

San Francisco, California 94105 

(415) 947-4130 

bohnenkamp.carol@epa.gov

Ginger Vagenas 

Office of Air Planning 

U.S. Environmental Protection Agency – Region 9 

75 Hawthorne Street 

San Francisco, California 94105 

(415) 972-3964 

vagenas.ginger@epa.gov 

 
3 

Table of Contents 

I. Interstate Transport and Arizona 

A. Clean Air Act Section 110(a)(2)(D)(i)(I) Requirements for the 2006 Fine 

Particulate Standards

B. Summary of Transport Assessment 

 1. Transport to Nonattainment Receptors in Western States 

 2. Transport to Maintenance Receptors in Western States 

3. Transport to Nonattainment and Maintenance Receptors in Eastern States 

C. Conclusion 

II. State of Arizona’s Assessment of Transport 

A. Summary of State of Arizona’s Assessment of Transport 

B. EPA’s Evaluation of the State of Arizona’s Assessment of Transport 

III. Transport Assessment Methodology 

A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology 

B. Factors Considered in the Transport Analysis for Nonattainment and Maintenance 

Receptors 

IV. Transport Assessment for Nonattainment Receptors 

A. Introduction 

B. Transport to Nearby States 

 1. Utah

 2. Nevada 

 3. California 

C. Transport to Other Western States – Oregon, Washington, Idaho, and Montana 

 1. Oregon 

 2. Washington 

 3. Idaho 

 4. Montana 

D. Transport to Eastern States 

V. Transport Assessment for Maintenance Receptors 

A. Introduction 

B. Transport to Nearby States 

1. California 

 2. Utah 

C. Transport to Eastern States 

 
4 

Appendices 

Appendix A – Nonattainment and Maintenance Receptors List 

1. List of Nonattainment and Maintenance Receptors 

Appendix B – Nonattainment Receptors 

1. EPA Region 9 States – California and Nevada 

2. EPA Region 8 States – Montana and Utah 

3. EPA Region 10 States – Idaho, Oregon, and Washington 

 

Appendix C – Maintenance Receptors 

1. EPA Region 9 States – California 

2. EPA Region 8 States – Utah 

Appendix D – PM2.5 Data – IMPROVE Data for Utah, Nevada, and California/Oregon Border 

Sites for the Years 2006-2010 

1. Map of IMPROVE Monitoring Sites 

2. Utah – IMPROVE Data for the Years 2006-2010 

 

3. Nevada – IMPROVE Data for the Years 2006-2010 

4. California/Oregon Border – IMPROVE Data for the Years 2006-2010 
1 

I. Interstate Transport and Arizona 

I.A. Clean Air Act Section 110(a)(2)(D)(i)(I) Requirements for the 2006 Fine Particulate

Standards

Section 110(a)(2)(D)(i)(I) of the Clean Air Act (CAA) requires each state to prohibit emissions 

that contribute significantly to nonattainment in, or interfere with maintenance by, any other state 

with respect to any primary or secondary national ambient air quality standard (NAAQS). The 

CAA requires states to submit plan provisions to address this requirement, among others, within 

three years after EPA’s promulgation of any new or revised NAAQS, or within such shorter 

period as EPA may prescribe. CAA section 110(a)(1). For purposes of implementing the 2006 

NAAQS for fine particulate matter (PM2.5), states were required to submit state implementation 

plan (SIP) provisions satisfying the requirements related to interstate transport in CAA section 

110(a)(2)(D)(i)(I) (among other section 110(a) requirements) by September 21, 2009. The rule 

establishing the revised PM2.5 NAAQS was signed by the Administrator and publically 

disseminated on September 21, 2006. Because EPA did not prescribe a shorter period for section 

110(a) infrastructure SIP submittals for these NAAQS, these submittals were due on September 

21, 2009, three years from the September 21, 2006 signature date pursuant to section 110(a)(1) 

of the CAA. See 42 U.S.C. 7410(a)(1). 

The Arizona Department of Environmental Quality (ADEQ) submitted a SIP revision to address 

the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2006 PM2.5 NAAQS, among other 

requirements, on October 14, 2009. See “Arizona State Implementation Plan Revision under 

Clean Air Act Section 110(a)(1) and (2): Implementation of 2006 PM2.5 [NAAQS], 1997 PM2.5 

[NAAQS], and 1997 8-hour Ozone [NAAQS],” September 2009 (“2009 Infrastructure SIP”).1 

Appendix B of the 2009 Infrastructure SIP (including attachments B1, B2, and B3) contains 

ADEQ’s assessment of potential interstate transport, entitled “Clean Air Act Section 

110(a)(2)(D)(i) – Interstate Transport Analysis for the 2006 PM2.5 National Ambient Air 

Quality Standards” (hereinafter “PM2.5 Transport Analysis”). Based on our evaluation of 

ADEQ’s submittal and other technical information, as discussed further below, we are proposing 

to approve the PM2.5 Transport Analysis and to conclude that additional control measures in 

Arizona are not necessary under CAA section 110(a)(2)(D)(i)(I) for the 2006 24-hour PM2.5 

NAAQS because emissions from Arizona sources do not contribute significantly to 

nonattainment or interfere with maintenance of these standards in any other state. 

I.B. Summary of Transport Assessment 

I.B.1. Transport to Nonattainment Receptors in Western States 

EPA reviewed the state of Arizona’s PM2.5 Transport Analysis and additional technical 

information to evaluate the potential for Arizona emissions to contribute significantly to 

 

1 ADEQ intended for this SIP submittal to also address all other requirements of CAA section 110(a), excepting 

section 110(a)(2)(G), for the 1997 8-hour ozone and PM2.5 NAAQS and the 2006 PM2.5 NAAQS. See letter dated 

October 14, 2009, from Eric C. Massey, Air Quality Director, ADEQ, to Laura Yoshii, Acting Regional 

Administrator, EPA Region 9, with enclosures. EPA has proposed to act on this submittal for purposes of 

addressing the other “infrastructure” requirements of CAA section 110(a) in a separate proposed rule published on 

June 27, 2012 (77 FR 38239). 
2 

nonattainment of the 2006 PM2.5 NAAQS at specified monitoring sites in the western United 

States. EPA first identified as “nonattainment receptors” all monitoring sites in the western states 

that had recorded PM2.5 design values above 35 micrograms per cubic meter (μg/m3), the level 

of the 2006 24-hour PM2.5 NAAQS, during the years 2008-2010.2 See section III below 

(discussing EPA’s methodology for selection of nonattainment receptors, and providing a list 

and map of western receptors). 

Because geographic distance is a relevant factor in the assessment of potential pollution 

transport, EPA focused its review on information related to potential transport of PM2.5 

pollution from Arizona to the states bordering Arizona that have nonattainment receptors: Utah, 

Nevada, and California. With respect to Utah and Nevada, EPA believes that the following 

factors support a finding that emissions from Arizona do not significantly contribute to 

nonattainment of the 2006 24-hour PM2.5 NAAQS in either of these states: (1) technical 

information indicating that elevated PM2.5 levels at nonattainment receptors are predominantly 

caused by local emission sources, and (2) air quality data indicating that regional background 

levels of PM2.5 are generally low during the time periods of elevated PM2.5 at these receptors. 

Similarly, with respect to California, technical information indicating that elevated PM2.5 levels 

at the nonattainment receptors are predominantly caused by local emission sources and that the 

dominant air flows across the State are from the west to the east support a finding that emissions 

from the state of Arizona do not significantly contribute to nonattainment of the 2006 24-hour 

PM2.5 standards in California. 

EPA also evaluated potential PM2.5 transport to nonattainment receptors in the more distant 

western states of Oregon, Washington, Idaho, and Montana. EPA believes that the following 

factors support a finding that emissions from Arizona do not significantly contribute to 

nonattainment of the 2006 24-hour PM2.5 NAAQS in any of these states: (1) the significant 

distance from the state of Arizona to the nonattainment receptors in these states, (2) technical 

information indicating that elevated PM2.5 levels at nonattainment receptors in these states are 

predominantly caused by local emission sources, and (3) air quality data indicating that regional 

background levels of PM2.5 are generally low during the time periods of elevated PM2.5 at these 

receptors. 

We discuss these evaluations in more detail below. 

I.B.2. Transport to Maintenance Receptors in Western States 

EPA reviewed the state of Arizona’s PM2.5 Transport Analysis and additional technical 

information to evaluate the potential for Arizona emissions to interfere with maintenance of the 

2006 24-hour PM2.5 standards at specified monitoring sites in the western U.S. EPA first 

identified as “maintenance receptors” all monitoring sites in the western states that had recorded 

PM2.5 design values above the level of the 2006 24-hour PM2.5 NAAQS (35 μg/m3) during the 

 

2 Because the Clean Air Interstate Rule (CAIR) did not cover states in the western United States, these data are not 

significantly impacted by the remanded CAIR and thus could be considered in this analysis. In contrast, recent air 

quality data in the eastern, midwestern and southern states are significantly impacted by reductions associated with 

CAIR and because the Transport Rule was developed to replace CAIR, EPA could not consider reductions 

associated with the CAIR in the base case transport analysis for those states. See 76 FR at 48223-24. 
3 

2006-2008 and/or 2007-2009 periods but below this standard during the 2008-2010 period.3See

section III below (discussing EPA’s methodology for selection of maintenance receptors). All of 

these maintenance receptors in the western states are located in California, Utah and Arizona. 

EPA thus evaluated the potential for transported Arizona emissions to interfere with maintenance 

of the NAAQS at California and Utah receptor locations.

4

 EPA believes that the following 

factors support a finding that emissions from Arizona do not interfere with maintenance of the 

2006 24-hour PM2.5 NAAQS in California: (1) technical information indicating that elevated 

PM2.5 levels at maintenance receptors in California are predominantly caused by local emission 

sources; and (2) technical information indicating that the dominant air flows across the State are 

from the west to the east. With respect to Utah, EPA believes that the following factors support a 

finding that emissions from Arizona do not interfere with maintenance of the 2006 24-hour 

PM2.5 NAAQS in this state: (1) technical information indicating that elevated PM2.5 levels at 

maintenance receptors are predominantly caused by local emission sources, and (2) air quality 

data indicating that regional background levels of PM2.5 are generally low during the time 

periods of elevated PM2.5 at these receptors. 

We discuss these evaluations in more detail below. 

I.B.3. Transport to Nonattainment and Maintenance Receptors in Eastern States 

EPA has also considered potential PM2.5 transport from Arizona emission sources to the nearest 

potential nonattainment or maintenance receptors located in the eastern states within the domain 

of the modeling analysis for the Cross State Air Pollution Rule (CSAPR) (76 FR 48208). The 

nearest nonattainment and/or maintenance receptor identified in the 2012 CSAPR modeling 

analysis is in Madison County, Illinois. The CSAPR modeling did not analyze the contribution 

of Arizona sources to Madison County, Illinois. Thus, EPA analyzed the magnitude of 

Arizona’s sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions relative to states found to 

have emissions that significantly contribute to nonattainment at that receptor. EPA also 

considered the distance of Arizona from Madison County, Illinois relative to states found to 

significantly contribute there. EPA believes that the following factors support a finding that 

emissions from Arizona sources do not significantly contribute to nonattainment or interfere with 

maintenance of the 2006 24-hour PM2.5 NAAQS at this location: (1) the relatively small 

magnitude of the emission inventory of PM2.5 precursors (SO2 and NOx) in Arizona combined 

with (2) the relatively long distance between the nearest portion of the state of Arizona to the 

Madison County, Illinois receptor.5 EPA believes that these factors also support a finding that 

emissions from Arizona sources do not contribute significantly to nonattainment or interfere with 

 

3 As noted above, EPA can consider data from these years for states in the western United States as such data is not 

impacted by the remanded CAIR. 

4 As this analysis is focused on interstate transport, EPA did not evaluate the impact of Arizona emissions on 

maintenance receptors within Arizona. 

5 Emission inventory data used for the Transport Rule modeling analyses indicate that SO2 emissions in Arizona are 

less than 10% of SO2 emissions in Texas, and that NOx emissions in Arizona are less than 20% of NOx emissions 

in Texas. Thus, the conclusion that Texas significantly contributes to nonattainment in Madison County, Illinois, 

which is also closer to Texas than to Arizona, does not demonstrate that emissions from Arizona similarly 

significantly contribute to Madison County. See “Emissions Inventory Final Rule TSD,” Technical Support 

Document (TSD) for the final Transport Rule, Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 

7-1 and 7-2. 
4 

maintenance of the 2006 24-hour PM2.5 NAAQS at any of the other CSAPR receptors, all of 

which are farther from Arizona than Madison County, Illinois. 

I.C. Conclusion 

EPA’s review of available technical information and air quality data supports the conclusion in 

Arizona’s PM2.5 Transport Analysis that emissions of direct PM2.5 and PM2.5 precursors from 

the state of Arizona do not significantly contribute to nonattainment in, or interfere with 

maintenance by, any other state with respect to the 2006 24-hour PM2.5 standards. 

Based on our evaluation of Arizona’s PM2.5 Transport Analysis and additional technical 

information, as discussed further below, EPA proposes to conclude that emissions of direct 

PM2.5 and PM2.5 precursors from the state of Arizona do not significantly contribute to 

nonattainment or interfere with maintenance of the 2006 24-hour PM2.5 standards in any other 

state and that CAA section 110(a)(2)(D)(i)(I) therefore does not require Arizona to adopt 

additional controls to prohibit such impacts. 

II. State of Arizona’s Assessment of Transport 

II.A. Summary of State of Arizona’s Assessment of Transport 

Arizona’s PM2.5 Transport Analysis contains the State’s assessment of the potential for 

emissions of PM2.5 and PM2.5 precursors from Arizona sources to significantly contribute to 

nonattainment or interfere with maintenance of the 24-hour PM2.5 standards in any other state.6 

The state considered topography and meteorology, stating that, “Generally dominant air flows 

across the State are from the west to the east and there are seasonal flows from the Gulf of 

Mexico to the southeast across Arizona to the northwest. The State asserts that natural mountain 

ranges in the eastern portion of the State prevent western flows from reaching New Mexico and 

other topographical features generally prevent Arizona generated pollutants from having 

significant transport capability into other nonattainment and maintenance areas.” The state also 

considered the level of emissions in the state of Arizona, and PM2.5 monitoring data. 

With respect to potential transport to the counties in California that share a border with Arizona 

(Imperial County, San Bernardino County, and Riverside County), Arizona’s PM2.5 Transport 

Analysis states that, “Based on regional and local flow patterns, California nonattainment areas 

are upwind of Arizona emission sources.” 

With respect to potential transport to the nonattainment counties in the northwestern part of 

Utah, the PM2.5 Transport Analysis states that the Utah nonattainment counties are 

“approximately 200 miles from the northern Arizona border and over 500 miles from the only 

recommended nonattainment designation in the state” of Arizona. 

Based on these analyses, ADEQ concludes that “monitored air quality data, the location of 

emission sources, topography and meteorology, and distance to downwind nonattainment areas 

 

6

See PM2.5 Transport Analysis at P.3 – P.9. 
5 

all demonstrate 24–hour PM2.5 and PM2.5 precursors do not significantly contribute to or 

interfere with maintenance of the 24-hour PM2.5 standards in any other state.”7 

II.B. EPA’s Evaluation of the State of Arizona’s Assessment of Transport 

Although ADEQ’s assessment in the PM2.5 Transport Analysis identifies several factors that are 

appropriate for consideration in the assessment of whether Arizona sources contribute 

significantly to nonattainment or interfere with maintenance of the 2006 PM2.5 NAAQS in other 

states, ADEQ’s conclusion that emissions from sources in Arizona do not cause either of these 

prohibited impacts is not supported by adequate technical information. As explained in Section 

III below, however, EPA is supplementing its evaluation of the PM2.5 Transport Analysis with 

additional technical information consistent with the methodologies and analyses developed in the 

Transport Rule (also called the “Cross-State Air Pollution Rule”)8in response to the judicial 

remand of the 2005 “Clean Air Interstate Rule.”9 Our proposed action takes into account both 

the State’s assessment in the PM2.5 Transport Analysis and our own supplemental assessment of 

relevant technical information, including the characteristics of the formation of elevated PM2.5 

at nonattainment and maintenance receptors in neighboring states, and ambient PM2.5 levels at 

monitoring sites representative of regional background in nearby states. This information is 

discussed further below. 

III. Transport Assessment Methodology 

III.A. Discussion of Nonattainment and Maintenance Receptor Selection Methodology 

On September 25, 2009, EPA issued a guidance memorandum that provides recommendations to 

states for making submissions to meet the requirements of CAA section 110(a)(2)(D)(i) for the 

2006 24-hour PM2.5 standards. See Memorandum from William T. Harnett, Director, Air 

Quality Policy Division, to Regional Air Division Directors, Regions I-X, “Guidance on SIP 

Elements Required Under Sections 110(a)(1) and (2) for the 2006 24-Hour Fine Particle (PM2.5) 

National Ambient Air Quality Standards (NAAQS),” September 25, 2009 (“2006 PM2.5 

NAAQS Infrastructure Guidance” or “Guidance” ).10 The Guidance recommends that each state 

explain in its section 110(a)(2)(D)(i)(I) SIP whether or not its emissions contribute significantly 

to nonattainment or interfere with maintenance of the NAAQS in any other state, and to address 

any such impacts. See Guidance at 3, 4. The Guidance states as follows: 

The state's conclusion must be supported by an adequate technical analysis. Information 

to support the state's determination with respect to significant contribution to 

nonattainment might include, but is not limited to, information concerning emissions in 

the state, meteorological conditions in the state and the potentially impacted states, 

monitored ambient concentrations in the state and the potentially impacted states, the 

distance to the nearest area that is not attaining the NAAQS in another state, and air 

 

7

Id.

8

75 FR 45210 (August 2, 2010) (proposed Transport Rule) and 76 FR 48208 (August 8, 2011) (final Transport 

Rule). 

9

70 FR 25172 (May 12, 2005). 

10 Available at: http://www.epa.gov/ttn/caaa/t1/memoranda/20090925_harnett_pm25_sip_110a12.pdf 
6 

quality modeling. The EPA believes that it would be appropriate for states to make this 

assessment by considering the impact of current or future emissions on nearby 

nonattainment areas, and evaluating the air quality impact and potential mitigation 

strategies.

11

To determine whether the CAA section 110(a)(2)(D)(i)(I) requirement is satisfied, EPA must 

determine whether a state’s emissions contribute significantly to nonattainment or interfere with 

maintenance in downwind areas. If this factual finding is in the negative, then section 

110(a)(2)(D)(i)(I) does not require any changes to a state’s SIP. If, however, the evaluation 

reveals that emissions from sources within the state do contribute significantly to nonattainment 

or interfere with maintenance in other states, then the state must adopt substantive provisions to 

eliminate those emissions. The state could achieve any required reductions through traditional 

command and control programs, or at its own election, through participation in a cap and trade 

program. Consistent with EPA's approach in the 1998 NOx SIP call, the 2005 CAIR, and the 

2011 Transport Rule,

12 EPA is evaluating these impacts with respect to specific monitors 

identified as having nonattainment and/or maintenance problems, which we refer to as 

“receptors.”13 EPA notes that no single piece of information is by itself dispositive of the issue. 

Instead, the total weight of all the evidence taken together is used to evaluate significant 

contributions to nonattainment or interference with maintenance of the 2006 24-hour PM2.5 

NAAQS in another state. 

A receptor may be a downwind location that is currently violating the PM2.5 NAAQS, has 

violated in the past, is projected to violate in the future, or may have trouble maintaining the 

NAAQS in the future. Nonattainment and maintenance receptors can be identified using future 

year modeling, recent ambient data, or both. 

If appropriate future year modeling is not available,14 nonattainment and maintenance receptors 

can be identified using recent ambient air quality monitoring data. For this action, we evaluated 

the three most recent consecutive 3-year periods for which complete, quality-assured and 

certified air quality data were available (covering a 5-year period) to calculate “design values”15

for those periods. Because EPA uses the most recent 3-year design value period for purposes of 

promulgating air quality designations and redesignations, it is logical to use the most recent 3-

year period to identify “nonattainment” receptors. However, previous violations of the NAAQS 

are indicative of an air quality problem that may return in the future. The year to year variability 

of emissions and/or meteorology may cause an area to have trouble maintaining the NAAQS in 

the future. Therefore, we have identified “maintenance” receptors by examining previous years 

 

11 Guidance at 3. 

12 See NOx SIP Call, 63 FR 57371 (October 27, 1998); CAIR, 70 FR 25172 (May 12, 2005); and Transport Rule or 

Cross-State Air Pollution Rule, 76 FR 48208 (August 8, 2011). 

13 Air quality designations are not relevant to the methodology for identifying these “receptors.” 

14 Available modeling data should be evaluated for the intended purpose. If modeling data is used to establish 

nonattainment and/or maintenance receptors, it should be for an appropriate future year (within the time frame of 

downwind attainment dates) and model performance should be shown to be acceptable for the upwind and 

downwind areas being considered. 

15 “Design value” means the “calculated concentration according to the applicable appendix of [40 CFR part 50] for 

the highest site in an attainment or nonattainment area.” 40 CFR 58.1 (definitions). 
7 

of data. This methodology is conceptually similar (although not identical) to the methodology 

that EPA used in the CSAPR to identify “nonattainment” and “maintenance” receptors. 

We applied the following methodology: 

Similar to the CSAPR analysis, we examined ambient data which spanned a 5-year period. This 

allows examination of year to year variability. The three most recent consecutive three-year 

design value periods are 2006-2008, 2007-2009, and 2008-2010.16 

1) Nonattainment receptors are those sites that are violating the NAAQS in the most recent 

3-year period.17 

2) Maintenance receptors are those receptors that show attainment in the most recent 3-year 

design value period (2008-2010) but violated the NAAQS in at least one of the previous 

two periods (2006-2008 and/or 2007-2009). 

Ambient data included the three most recent official design value periods available at the time of 

the analysis. The official design values are posted by EPA’s Office of Air Quality Planning and 

Standards (OAQPS) on the Air Trends website and are available at: 

http://www.epa.gov/airtrends/values.html. A list of receptors selected for this interstate transport 

analysis is shown below in Figure III.A.1., and the corresponding map of receptors is shown 

below in Figure III.A.2. Receptors with PM2.5 design values above the PM2.5 standard of 

35μg/m3for the years 2008 through 2010 are listed as nonattainment receptors. Receptors with 

PM2.5 design values at or below the PM2.5 standard of 35μg/m3for 2008-2010 but above the 

standard for at least one of the previous 3-year periods (2006-2008 or 2007-2009) are listed as 

maintenance receptors. Based on this methodology, New Mexico, Colorado, and Wyoming do 

not contain any nonattainment or maintenance receptors. 

To evaluate the potential for significant contribution to nonattainment in other states, EPA first 

evaluated potential transport to the nearest states with identified nonattainment receptors. The 

states bordering Arizona with nonattainment receptors are California, Utah, and Nevada. EPA 

then evaluated potential transport to other western states with nonattainment receptors located 

farther away, i.e., Oregon, Washington, Idaho, and Montana. To evaluate the potential for 

interference with maintenance in other states, EPA evaluated potential transport to maintenance 

receptors in Utah and California, which are the only western states (outside of Arizona) with 

identified maintenance receptors. 

 

 

16 As noted above, EPA can consider data from these years for states in the western United States as such data is not 

impacted by the remanded CAIR. 

17 When evaluating recent design values, it is not necessary to average the design values together to create a fiveyear weighted average. Weighted average data is only necessary when projecting modeling data to the future, since 

modeled projections are generally based on only a single year (or less) of modeled meteorology. 
8 

Table III.A.1. List of Western Counties with Daily PM2.5 

Nonattainment or Maintenance Receptors 

State County AIRS ID Design Value 

2006-08 

Design Value 

2007-09 

Design Value 

2008-10 

Receptor 

Type 

Arizona Pinal 040213013 48 NA 40 NA 31 A Maintenance 

Arizona Santa Cruz 040230004 40 NA 31 A 32 A Maintenance 

California Alameda 060010007 36 NA 34 A 30 A Maintenance 

California Butte 060070002 69 NA 59 NA 51 NA Nonattainment 

California Fresno 060190008 58 NA 60 NA 54 NA Nonattainment 

California Imperial 060250005 36 NA 34 inc-a 32 inc-a Maintenance 

California Inyo 060271003 34 inc-a 38 NA 36 NA Nonattainment 

California Kern 060290016 70 NA 70 NA 65 NA Nonattainment 

California Kings 060310004 52 NA 53 NA 49 NA Nonattainment 

California Los Angeles 060370002 41 NA 42 NA 38 NA Nonattainment* 

California Merced 060472510 50 NA 51 NA 45 NA Nonattainment 

California Orange 060590007 38 NA 37 NA 30 A Maintenance 

California Riverside 060658005 53 NA 49 NA 41 NA Nonattainment* 

California Sacramento 060670006 54 NA 49 NA 40 NA Nonattainment* 

California San Bernardino 060712002 52 NA 48 NA 37 NA Nonattainment* 

California San Diego 060731011 9 inc-a 9 inc-a 43 NA Nonattainment 

California San Joaquin 060771002 51 NA 50 NA 44 NA Nonattainment 

California Santa Clara 060850005 36 NA 34 A 30 A Maintenance 

California Solano 060950004 36 NA 36 NA 31 A Maintenance 

California Stanislaus 060990006 67 inc-na 60 inc-na 55 NA Nonattainment 

California Sutter 061010003 47 NA 42 NA 36 NA Nonattainment 

California Tulare 061072002 57 NA 59 NA 51 NA Nonattainment 

Idaho Franklin 160410001 27 inc-a 31 inc-a 46 NA Nonattainment 

Idaho Shoshone 160790017 34 A 34 A 36 NA Nonattainment 

Montana Silver Bow 300930005 32 A 32 A 38 NA Nonattainment 

Nevada Washoe 320310016 35 A 39 NA 38 NA Nonattainment 

Oregon Klamath 410350004 46 NA 47 NA 45 NA Nonattainment 

Oregon Lake 410370001 41 inc-na 41 NA 38 NA Nonattainment 

Oregon Lane 410392013 40 NA 41 NA 38 NA Nonattainment 

Utah Box Elder 490030003 35 A 37 NA 42 NA Nonattainment 

Utah Cache 490050004 36 NA 40 NA 43 NA Nonattainment 

Utah Davis 490110004 35 A 38 NA 38 NA Nonattainment 

Utah Salt Lake 490350003 45 NA 48 NA 45 NA Nonattainment* 

Utah Utah 490494001 44 NA 50 NA 41 NA Nonattainment* 

Utah Weber 490570002 36 NA 41 NA 38 NA Nonattainment* 

Washington Pierce 530530029 44 NA 46 NA 38 NA Nonattainment 

Washington Yakima 530770009 36 inc-na 37 NA 37 NA Nonattainment 

NA = Not attaining; A = attaining; inc-na = incomplete/not attaining; inc-a = incomplete/attaining 

* = This county contains both nonattainment and maintenance receptors. See Appendix A of this TSD for more 

details. 

 
9 

Figure III.A.2: Map of Daily PM2.5 Nonattainment and Maintenance Receptors

III.B. Factors Considered in Transport Analysis for Nonattainment and Maintenance 

Receptors. 

Consistent with the recommendations in the Guidance, EPA reviewed emission inventory data, 

ambient monitoring data, and meteorological conditions within the state of Arizona. In addition, 

EPA reviewed PM2.5 monitoring data in areas representative of western regional background 

levels of PM2.5 in the nearby states of Utah and Nevada as well as selected remote monitoring 

sites on the California-Oregon border. Finally, EPA reviewed technical information related to 

each of the nonattainment and maintenance receptors in the potentially impacted states, including 

meteorological conditions and ambient PM2.5 monitoring data. 

Specifically, EPA reviewed the emission inventory data submitted as part of Arizona’s PM2.5 

Transport Analysis. Based on 2005 data in the USEPA National Emission Inventory, the PM2.5 

Transport Analysis provides statewide emissions data as follows: 313,486 tons of NOx, 92,138 

tons of SO2 and 132,862 tons of PM2.5.18 The monitored ambient PM2.5 concentrations for 

nonattainment and maintenance receptors in the state of Arizona are shown above in Figure 

 

18 See PM2.5 Transport Analysis, Attachment B2: “Arizona Nitrogen Oxides, PM2.5 and Sulfur Dioxide Emissions 

Inventories.” 
10 

III.A.1, “List of Daily PM2.5 Nonattainment and Maintenance Receptors.” All design values for 

the time period 2008-2010 within the state of Arizona are below the PM2.5 24-hour standard of 

35μg/m3. Pinal County has design values above 35μg/m3 for the earlier time periods of 2006-08 

and 2007-09, and Santa Cruz County has design values above 35μg/m3 for 2006-08. 

EPA then reviewed PM2.5 monitoring data from relatively remote ambient air monitoring sites 

that EPA believes is representative of regional background PM2.5 levels in the western United 

States. EPA reviewed five years of data collected at the IMPROVE19 monitoring network at each 

of eight National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and Arches National Parks) 

and Nevada (Jarbidge Wilderness Area and Great Basin National Park), and at the CaliforniaOregon border (Lava Beds National Monument and Crater Lake National Park). Ambient PM2.5 

monitoring data, as well as chemical species data (ammonium nitrate, ammonium sulfate, 

elemental carbon, organic carbon, sea salt, and soil) is available for each of these monitoring 

sites. We provide monitored PM2.5 data from each of these monitoring sites during the 2006-

2010 period, for each day when measurements occurred, as well as a map of the site locations in 

Appendix D of this TSD. This provides information about regional background levels of PM2.5 

in the states surrounding Arizona, as well as the chemical composition of the PM2.5 in these 

areas. 

Most of the elevated levels of PM2.5 in the western states are measured during the winter 

months. For example, of the 17 days with measured values above the standard in 2010 in Salt 

Lake City, eleven days were in January (with levels up to 76μg/m3), and four days were in 

December (with levels up to 53μg/m3). The remaining two days above the standard were March 

30 and April 27. 

The PM2.5 data for each of the eight IMPROVE monitoring sites indicate low background 

PM2.5 levels throughout the year, but especially during the winter months for each of the years 

from 2006 through 2010. For example, the PM2.5 values for January and December of 2010 at 

Bryce Canyon National Park, Utah are below 3μg/m3. 

In the winter, when the measured PM2.5 values in Salt Lake City are as high as 76 μg/m3, the 

PM2.5 values in remote areas are very low (below 3 μg/m3), indicating that over 90% of the PM 

in the urban area is locally generated. Because the PM2.5 at these locations is local in nature, it is 

reasonable to conclude that emissions from Arizona do not have a significant impact on 

nonattainment in Salt Lake City. In contrast, an analysis of the CSAPR 2012 nonattainment and 

maintenance receptors shows that a large fraction of the daily PM2.5 concentrations in Eastern 

areas are from upwind states. For the 41 CSAPR daily PM2.5 nonattainment and maintenance 

receptors, the modeled upwind sulfate plus nitrate contribution to total PM2.5 ranged from a low 

 

19 The Interagency Monitoring of Protected Visual Environments (IMPROVE) program is a cooperative 

measurement effort governed by a steering committee composed of representatives from Federal and regional-state 

organizations. The IMPROVE monitoring program was established in 1985 to aid the creation of Federal and State 

implementation plans for the protection of visibility in Class I areas. The objectives of IMPROVE include 

establishing current aerosol conditions in mandatory class I areas; and identifying chemical species and emission 

sources responsible for existing man-made visibility impairment. 

http://vista.cira.colostate.edu/improve/Overview/IMPROVEProgram_files/frame.htm
11 

of 20% to a high of 53% with a median value of 37%.20 Since CSAPR only tracked the 

contributions of sulfate and nitrate, these values represent the minimum percentage of upwind 

contribution to the receptors. Accounting for transport of additional primary PM2.5 species 

would only increase the upwind percentage and therefore decrease the percentage of PM2.5 due 

to local sources. 

Figure III.B.1. IMPROVE PM2.5 Data for Bryce Canyon National Park for the Year 2010 

In addition to reviewing background monitoring data which indicates that the elevated PM2.5 

levels are not likely due to regional transport, EPA reviewed technical information, such as 

meteorological conditions and monitored ambient data, related to each of the areas with 

nonattainment and maintenance receptors in the potentially impacted states to determine whether 

local emissions cause or contribute to the elevated PM2.5 levels at these locations. We discuss 

our evaluation for each of the areas with receptors in the following sections. 

IV. Transport Assessment for Nonattainment Receptors 

IV.A. Introduction 

Based on our methodology for selecting nonattainment receptors in Section III.A, above 

(Discussion of Nonattainment and Maintenance Receptor Selection Methodology), EPA has 

identified nonattainment receptors in seven western states: Utah, Nevada, California, Oregon, 

Washington, Idaho, and Montana. EPA has evaluated technical information regarding transport 

for each of the areas with nonattainment receptors identified above, following the methodology 

discussed in Section III. B. Transport to the states which border Arizona and have nonattainment 

receptors (Utah, Nevada, and California) is addressed first. Transport to the more distant western 

 

20 See Memorandum to File, Brian Timin, EPA, Office of Air Quality Planning and Standards, “CSAPR Daily 

PM2.5 Upwind Contribution,” July 2012.
12 

states with nonattainment receptors (Oregon, Washington, Idaho, and Montana) are then 

addressed. Finally, transport to eastern states is addressed. 

IV.B. Transport to Nearby States 

IV.B.1. Utah21

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months.

22

The levels of elevated PM2.5 in the Salt Lake City 2006 PM2.5 nonattainment area and the 

Provo 2006 PM2.5 nonattainment area are primarily due to local emissions, as noted in the 

discussion of Salt Lake City and Provo nonattainment areas below. 

Of the 17 days with measured values above the standard in 2010 in Salt Lake City, eleven days 

were in January (with levels up to 76μg/m3), and four days were in December (with levels up to 

53μg/m3). The remaining two days above the standard were March 30 and April 27. 

During the winter months, levels of PM2.5 at background monitoring sites located north of 

Arizona and south of the Utah nonattainment receptors23 are very low, generally below 3μg/m3, 

indicating that over 90% of the PM in the urban area is locally generated. As discussed above, 

this supports our finding that PM2.5 levels are not likely to be caused by regional elevated 

PM2.5 levels. The local nature of the PM2.5 levels during the time period when the standard is 

exceeded and the low levels of background PM2.5 during these time periods support our finding 

that emissions from the state of Arizona do not contribute significantly to nonattainment of the 

PM2.5 standard at these nonattainment receptors. 

Box Elder, Davis, Salt Lake, Tooele, and Weber Counties (Greater Salt Lake Area)

All of Davis and Salt Lake counties, and portions of Box Elder, Tooele and Weber counties are 

designated as part of the Salt Lake City (SLC) 2006 PM2.5 nonattainment area (NAA). The SLC 

NAA is situated in a valley bordered on the west by the Stansbury Mountains,24 Promontory 

Mountains and Great Salt Lake, and on the east by the Wasatch Front. During inversions, the 

NAA becomes a closed airshed (save for potential transport between the Salt Lake City and 

Provo NAAs) featuring stagnant air masses and light winds which typically oscillate back and 

forth within the airshed. As the airshed is essentially capped during inversions, PM2.5 is formed 

in-situ (and trapped) via fresh locally derived emission sources and secondary chemistry.

25

 

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Salt Lake City is 58% ammonium nitrate, 31% carbon and organic 

 

21 For discussion of the Idaho/Utah – Franklin County/Cache County area, see section IV.3.C Idaho of this TSD. 

22 See Appendix E at E.1. 

23 IMPROVE monitoring network at each of six National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and 

Arches National Parks) and Nevada (Jarbidge Wilderness Area and Great Basin National Park), 

24 The Quqirrh Mountains lie between the Wasatch Front and the Stansbury Mountains. However, EPA determined 

that some areas located west of the Quqirrh Mountains should still be considered part of the SLC nonattainment 

area. 

25 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008, Index 583-669 at 40. 
13 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

mobile, point, and area sources contribute to primary and secondarily formed PM2.5 that violate 

the standard during stable weather events associated with strong inversions. 

Utah County (Provo-Orem)

A large portion of Utah County is designated as the Provo 2006 PM2.5 nonattainment area. The 

Provo NAA is situated in the Utah Valley. Like the other low-lying valleys just west of the 

Wasatch Front, the topography of the Utah Valley makes it prone to temperature inversions. 

During inversions, the Provo NAA features stagnant air masses and calm to light winds. As the 

airshed is essentially capped, PM2.5 is formed in-situ (and trapped) via fresh locally derived 

emission sources and secondary chemistry.

26 Transport of air masses between the Salt Lake City 

and Provo NAAs can occur during inversions, as there is a 4.75-mile gap in the mountains 

separating these airsheds that is below the approximate average inversion height for these 

areas.27 

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Provo is 71% ammonium nitrate, with 21% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

amounts of emissions from mobile, point, and area sources, contribute to ambient levels of 

primary and secondarily formed PM2.5 that violate the standard during stable weather events 

associated with strong inversions. 

IV.B.2. Nevada 

PM2.5 formation at the nonattainment receptor in Nevada is discussed in detail in Appendix B 

and is summarized below. 

Elevated PM2.5 levels in the Reno area occur during wintertime stagnation episodes. The highest 

values are generally measured in January and December. 

28 Wildfires in June and July of 2008 

had a large impact on PM2.5 concentrations in this area; however, the Washoe County Health 

District has flagged the affected data as exceptional events.29 

The IMPROVE PM2.5 monitoring data for the Nevada sites, shown in Appendix D, show very 

low levels of PM2.5 (below 3μg/m3) for the months of January and December for each of the 

years from 2006 through 2010. 

The local nature of the PM2.5 levels during time period when the standard is exceeded and the 

low levels of background PM2.5 during these time periods support our finding that emissions 

 

26 Id.

27 Id. at 41. 

28 Washoe County, Nevada Air Quality Trends (2002-2011). 

http://www.co.washoe.nv.us/repository/files/4/Washoe-County-Air-QualityTrends-2002-2011.pdf

29 Washoe County, Nevada Air Quality Trends (2002-2011). 

http://www.co.washoe.nv.us/repository/files/4/Washoe-County-Air-QualityTrends-2002-2011.pdf
14 

from the state of Arizona do not contribute significantly to nonattainment of the PM2.5 standard 

at these nonattainment receptors. 

IV.B.3. California 

Transport to nonattainment receptors in California is discussed in detail in Appendix B and is 

summarized below. 

Northern California – Butte, Sacramento, and Sutter Counties

In Northern California, monitored exceedances of the PM2.5 standard appear to result from 

complex topography and localized emissions occurring during wintertime temperature inversions 

with low winds that persist for several days in an area that traps emissions. The speciation data 

from high concentration days indicates that as much as 75% of the concentrations are due to 

organic carbon, which also indicates that residential wood burning emissions are the dominant 

source.30

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, which occur during wintertime temperature inversions with low winds that persist for 

several days in an area that traps emissions, together with complex topography and the distance 

of the area from Arizona, we believe it is reasonable to conclude that emissions from Arizona 

sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 NAAQS at 

these receptor locations. 

Central California – Fresno, Kern, Kings, Merced, San Joaquin, Stanislaus, and Tulare Counties

In Central California, the monitored exceedances of the PM2.5 standard appear to result from 

complex topography and localized emissions occurring during wintertime temperature inversions 

with low winds that persist for several days in an area that traps emissions together with complex 

topography. The speciation data from high concentration days indicate high levels of secondary 

nitrate. On some days elevated levels of organic carbon indicate that residential wood burning 

also contributes to elevated levels of PM2.5. 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, which occur during wintertime temperature inversions with low winds that persist for 

several days in an area that traps emissions, together with complex topography and the distance 

of the area from Arizona, we believe it is reasonable to conclude that emissions from Arizona 

sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 standard at 

these receptor locations. 

Southern California – Los Angeles, Riverside, and San Bernardino Counties

PM2.5 in Southern California is essentially a combustion-generated pollutant and is associated 

with the volume of traffic, and numbers of sources (both point and area) located in the region. It 

 

30 ARB Almanac website (2006) http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm)
15 

is important to note that the areas with the highest concentrations of PM2.5 are directly 

downwind of an area with major ammonia sources associated with dairies and poultry farming. 

Eastern California – Inyo County

Elevated levels of PM2.5 in Inyo County are measured at a single monitor, the Keeler monitor, 

which is located adjacent to the Owens Lake Bed. The Owens Lake Bed is surrounded by steep 

terrain. EPA believes that given the proximity of the monitor to a large local source of particulate 

matter and the nearby terrain, it is reasonable to conclude that emissions from Arizona sources 

do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 standard at this 

monitor. 

California/Mexico Border – San Diego County 

The La Posta receptor is classified as a nonattainment receptor, based on a single measured 

PM2.5 value of 114 μg/m3 measured on June 1, 2010. All other measured values of PM2.5 at the 

La Posta monitoring site are very low. On June 1, 2010, the La Posta monitor recorded the 

highest measured value in the entire state of California, and 99% of the PM2.5 values for the rest 

of the State were below 20 μg/m3. The monitoring site is located 95 miles from the border of 

Arizona. The monitored PM2.5 levels at the two operating monitors in Imperial County, which is 

located to the east of San Diego County and west of Arizona, on June 1, 2010 were 7.12μg/m3

and 10.2μg/m3. 

The level of PM2.5 measured at the La Posta monitor on June 1, 2010 appears to be from local 

sources, which supports our finding that emissions from Arizona sources do not significantly 

contribute to the elevated PM2.5 levels at this location. 

IV. C. Transport to Other Western States – Oregon, Washington, Idaho and Montana 

IV.C.1. Oregon 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring site31 are representative of regional background PM2.5 in southern Oregon, and is 

consistently low (below 3μg/m3

) in the wintertime. The available data for each of the three areas 

with nonattainment receptors, discussed below, indicate that the cause of elevated PM2.5 levels 

is local. 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, which occur during wintertime temperature inversions with low winds that persist for 

several days in an area that traps emissions, together with complex topography, the low 

background levels of PM2.5 in the area, and the distance of the area from Arizona, we believe it 

is reasonable to conclude that emissions from Arizona sources do not significantly contribute to 

nonattainment of the 2006 24-hour PM2.5 standard at these receptor locations. 

 

31 See Appendix D of this TSD. 
16 

Klamath County (Klamath Falls)

 

A portion of Klamath County is designated nonattainment for the 2006 PM2.5 NAAQS. Klamath 

Falls is a relatively small urban community located in and supporting a vast rural area in southcentral Oregon. 

The state of Oregon’s analysis includes a 2005 emission inventory that shows that wood stove 

emissions are the most significant source of emissions. Additional air quality monitoring data 

provide supporting evidence that residential wood combustion emissions are the primary cause of 

exceedance days. Data show that exceedances occur during winter months, at a time when 

woodstoves are contributing to smoke in the area. Exceedances occurred from December through 

January, corresponding directly with the winter wood heating season, indicating the exceedances 

(except for flagged wildfire events) are a seasonal occurrence. 

Speciation data analysis indicates most of the PM2.5 comes from elemental and organic carbon, 

typical indicators of combustion activities such as wood burning. Meteorological data from 

Klamath Falls show that low wind speeds dominate during violating days, and the Klamath Falls 

area experiences frequent winter-time nocturnal inversions, when PM pollution can build up over 

time. Diurnal concentrations of PM2.5 are observed by hourly light scatter data that correspond 

closely with night-time use of woodstoves. Night-time inversions coupled with low wind speeds 

strongly suggest that pollution in the Klamath Falls area is a localized effect heavily influenced by 

the use of woodstoves. 

EPA Region 10’s Positive Matrix Factor receptor modeling identified the 6 factors contributing 

to elevated wintertime PM2.5 including wood smoke (65%), organic pyrolysis rich (23%), and 

smaller contributions by other identified factors (nitrate rich, soil, sulfate rich, and urban 

unidentified). 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, which occur during wintertime temperature inversions with low winds that persist for 

several days in an area that traps emissions, together with complex topography and the distance 

of the area from Arizona, we believe it is reasonable to conclude that emissions from Arizona 

sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 standard at 

these receptor locations. 

Lane County (Oakridge)

A portion of Lane County is designated nonattainment for the 2006 PM2.5 NAAQS. 

EPA’s technical analysis points to residential home heating, using wood burning appliances, as 

the main contributors to fine particle pollution in this area. EPA Region 10’s Positive Matrix 

Factor receptor modeling identified seven factors which contribute to elevated wintertime PM2.5 

including wood smoke (76%), organic pyrolysis rich (15%), as well as smaller contributions by 

other identified factors (gasoline vehicles, iron rich, sulfate rich, sea salt, and soil). 
17 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring sites32 are representative of regional background PM2.5 in southern Oregon, and are 

consistently low (below 3μg/m3) in the wintertime. 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, monitoring data indicating that regional levels of PM2.5 are low, and the distance of 

the area from Arizona, we believe it is reasonable to conclude that emissions from Arizona 

sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 standard at 

these receptor locations. 

Lake County (Lakeview)

EPA Region 10’s Positive Matrix Factor receptor modeling identified seven factors contributing to 

PM2.5 including wood smoke (67%), organic pyrolysis rich (13%), nitrate rich (7%), soil (5%), 

and smaller contributions by other identified factors (sulfate rich and urban unidentified). 

PM2.5 monitoring data from the Crater Lake National Park and Lava Beds IMPROVE 

monitoring sites33 are representative of regional background PM2.5 in southern Oregon, and are 

consistently low (below 3μg/m3) in the wintertime. 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, the monitoring data, which indicate that regional levels of PM2.5 are low, and the 

distance of the area from Arizona, we believe it is reasonable to conclude that emissions from 

Arizona sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 

standard at these receptor locations. 

IV.C.2. Washington 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions and the distance of the area from Arizona, we believe it is reasonable to conclude that 

emissions from Arizona do not significantly contribute to nonattainment of the 24-hour PM2.5 

standard at either of the two nonattainment receptor locations in the state of Washington. 

Pierce County (Tacoma)

The state of Washington’s analysis indicates that wood smoke associated with home heating 

is the largest source of PM2.5 in the Tacoma-Pierce County nonattainment area. Surface 

measurements at multiple sites suggest that the only design values which violate the 2006 

PM2.5 NAAQS are in the core of the nonattainment area, within about 3 kilometers (km) of 

the South L St. monitor. Beyond about 3-5km, the design values drop and are well below the 

NAAQS. 

 

32 Id.

33 Id.
18 

Yakima County (Yakima)

EPA Region 10’s Positive Matrix Factor receptor modeling identified 10 factors 

contributing to elevated wintertime PM2.5 including wood smoke (24%), nitrate rich 

(24%), gasoline vehicles (16%), organic pyrolysis rich (9%), sulfate rich (7%), and smaller 

contributions from other identified factors (iron rich, sea salt, soil, zinc rich, and urban 

unidentified). 

IV.C.3. Idaho 

EPA believes that the factors that indicate the elevated PM2.5 levels at these locations are 

caused by local emissions combined with the distance of the area from Arizona support our 

finding that emissions from Arizona do not contribute to nonattainment of the 24-hour PM2.5

standard at the nonattainment receptors in the state of Idaho. 

Franklin County/Cache County

Portions of Franklin County, Idaho and Cache County, Utah are designated as part of the 

Cache Valley 2006 PM2.5, two-state, nonattainment area. Limited chemical speciation data 

in the Cache Valley indicates the PM2.5 problem is dominated by ammonium nitrate aerosol. 

Transport of PM2.5 and precursors from the rural regions at the domain periphery is very 

small and most of the observed Wasatch Front and Cache Valley PM2.5 is formed in-situ 

(and trapped) via fresh locally derived emission sources and secondary chemistry. 

Local heating emissions from woodstoves, emissions from agricultural activities, and mobile 

emissions may contribute to violations of the PM2.5 NAAQS during stable weather events 

associated with extremely strong inversions as they are trapped in the Cache Valley due to 

temperature inversions, low wind, and local topography. 

Shoshone County (Pinehurst)

Information from the state of Idaho indicates that emissions from woodstoves contribute to 

primary PM2.5 that violates the standard during stable weather events associated with strong 

inversions. These emissions and the related effects are limited to the city of Pinehurst airshed, 

as they are trapped there due to temperature inversions, low wind, and local topography. 

IV.C.4. Montana 

EPA believes that the factors that indicate the elevated PM2.5 levels at these locations are 

caused by local emissions combined with the distance of the area from Arizona support our 

finding that emissions from Arizona do not contribute to nonattainment of the 24-hour 

PM2.5 standard at the nonattainment receptor in the state of Montana. 
19 

Silver Bow County (Butte)

Elevated levels of PM2.5 in the Butte area occur primarily in the winter months.34 The 

Butte area is topographically prone to wintertime temperature inversions, as it is situated in 

a montane valley. Speciation data indicates that emissions from wood smoke are the 

primary contributor to exceedances of the PM2.5 standard in Butte.35 These factors 

indicate that high levels of PM2.5 in Butte are driven by local emissions, which become 

trapped and build during wintertime inversions. 

IV.D. Transport to Eastern States 

EPA has also considered potential PM2.5 transport from Arizona emission sources to the nearest 

potential nonattainment or maintenance receptors located in the eastern, midwestern and 

southern states within the domain of the modeling analysis for the Cross State Air Pollution Rule 

(CSAPR) (76 FR 48208). The nonattainment and/or maintenance receptor nearest to Arizona 

identified in the 2012 CSAPR modeling analysis is Madison County, Illinois. The CSAPR 

modeling did not analyze the contribution of Arizona sources to Madison County, Illinois. Thus, 

EPA analyzed the magnitude of Arizona’s SO2 and NOx emissions relative to states found to 

have emissions that significantly contribute to nonattainment at that receptor. EPA also 

considered the distance of Arizona from Madison County, Illinois relative to states found to 

significantly contribute there. EPA believes that the following factors support a finding that 

emissions from Arizona sources do not contribute significantly to nonattainment of the 2006 24-

hour PM2.5 NAAQS at this receptor: (1) the relatively small magnitude of the emission 

inventory of PM2.5 precursors (SO2 and NOx) in Arizona, combined with (2) the relatively long 

distance between Arizona and this receptor. EPA believes that these factors also support a 

finding that Arizona does not contribute significantly to nonattainment of the 2006 24-hour 

PM2.5 NAAQS at any of the other CSAPR receptors farther east. 

In the CSAPR modeling, EPA did not quantify the PM2.5 contributions from Arizona to Illinois 

or any of the other Eastern nonattainment and maintenance receptors. However, we can make a 

qualitative conclusion about the likely contribution from Arizona to Illinois and points farther 

east by comparing the Arizona emissions to a state that was modeled in CSAPR. Texas is the 

nearest state to Arizona that was found to significantly contribute to downwind nonattainment in 

CSAPR. And in fact, Texas was found to contribute significantly to the nonattainment receptor 

in Madison County, Illinois. The 24-hour PM2.5 contribution from Texas to Madison County 

was above the 1% threshold (0.35 μg/m3) used in CSAPR to identify contributions that were 

considered not significant (the Texas contribution was 0.37 μg/m3). EPA has evaluated the 

relative amounts of PM2.5 precursor (SO2 and NOx) emissions in Arizona compared to the 

amounts of PM2.5 precursor emissions in Texas, as modeled in the 2012 CSAPR “base case.” 

The emission inventories used in the CSAPR modeling analyses indicate that SO2 emissions in 

Arizona are less than 10% of SO2 emissions in Texas, and NOx emissions in Arizona are less 

than 20% of NOx emissions in Texas. Specifically, the CSAPR “2012 Base Case” inventories 

provide the following statewide emissions inventory data for these two states: 274,608 tons of 

NOx and 65,046 tons of SO2 from Arizona emission sources, compared to 1,501,170 tons of 

 

34 See Appendix E of this TSD at E.2. 

35 Id at E.3. 
20 

NOx and 712,582 tons of SO2 from Texas emission sources.36 Even though the relationship 

between upwind emissions and downwind secondary PM2.5 formation is not linear, we would 

expect the Arizona PM2.5 contribution to Illinois to be much less than that of Texas and well 

below the 1% threshold. In addition, the distance from the closest part of Arizona to Madison 

County, Illinois (975 miles) is more than twice the distance to Madison County from the closest 

part of Texas (415 miles). The distance from Arizona to the other eastern receptors is even 

greater, therefore, the expected impact is somewhat smaller. Given all of these factors, EPA 

believes it is reasonable to conclude that emissions of PM2.5 and PM2.5 precursors from 

Arizona sources do not significantly contribute to nonattainment of the 2006 24-hour PM2.5 

NAAQS in any eastern state. 

V. Transport Assessment for Maintenance Receptors 

V.A. Introduction 

Based on our methodology for selecting maintenance receptors in Section III.A, above 

(Discussion of Nonattainment and Maintenance Receptor Selection Methodology), EPA has 

identified maintenance receptors in only three western states: California, Utah, and Arizona. 

Thus, to evaluate the potential for Arizona emissions to interfere with maintenance in other 

states, we have evaluated technical information related to the maintenance receptors only in 

California and Utah. As this analysis focuses on interstate transport, EPA did not evaluate the 

impact of Arizona emissions on maintenance receptors within Arizona. 

V.B. Transport to Nearby States 

V.B.1. California 

Transport to maintenance receptors in California is discussed in detail in Appendix C and 

summarized below. 

Northern California/San Francisco Bay Area – Alameda, Solano, and Santa Clara County 

Receptors

The receptors in these counties are in the San Francisco Bay airshed. The monitored values of 

PM2.5 that exceed the standard likely reflect localized sources because they occur during 

wintertime temperature inversions with low winds that persist for several days, allowing directly 

emitted and secondary PM2.5 to build up over a few days. The Bay Area Air Quality 

Management District analyses show that during the winter peak season, wood burning can 

account for 33 to over 80 percent of the PM2.5 concentrations. Ammonium nitrate and 

elemental carbon from diesel sources can also contribute to these high values. 

EPA believes that the factors that indicate the elevated PM2.5 levels at these locations are caused 

by local emissions and the distance of the area from Arizona support our finding that emissions 

from Arizona do not interfere with maintenance of the 24-hour PM2.5 standard at this receptor. 

 

36 See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, 

Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 7-1 and 7-2. 
21 

Southern California – Orange County (Maintenance Only) and Los Angeles, Riverside, San 

Bernardino Counties 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, regional and local flow patterns, and the location of California nonattainment areas 

generally upwind of Arizona emission sources, we believe it is reasonable to conclude that 

emissions from Arizona do not interfere with maintenance of the 2006 24-hour PM2.5 standard 

at this receptor. 

California/Mexico Border – Imperial County 

The high monitored levels of PM2.5 are limited to the Calexico – Ethel Street monitoring site, 

which is located near the Mexican Border. The elevated PM2.5 levels occur primarily in the 

winter months during stagnation conditions, when long distance transport is unlikely. On days of 

elevated PM2.5 at the Calexico Ethel Street monitor, the levels of PM2.5 measured at the other 

monitors in Imperial County, the Brawley and El Centro sites, are lower on all days. The PM2.5 

appears to be from a local source near the California/Mexico Border. These factors support our 

finding that emissions from Arizona sources do not interfere with maintenance of the 24-hour 

PM2.5 standard at this receptor. 

 

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, regional and local flow patterns, and the location of California nonattainment areas 

generally upwind of Arizona emission sources, we believe it is reasonable to conclude that 

emissions from Arizona do not interfere with maintenance of the 2006 24-hour PM2.5 standard 

at this receptor. 

Northern California – Sacramento County

In Northern California, monitored exceedances of the PM2.5 standard likely reflect localized 

sources occurring during wintertime temperature inversions with low winds that persist for 

several days in an area that trap emissions together with complex topography. The speciation 

data from high concentration days indicates that the PM2.5 has a high carbon mass, which also 

indicates that residential wood burning emissions are the dominant source.37

Given the factors that indicate the elevated PM2.5 levels at these locations are caused by local 

emissions, which occur during wintertime temperature inversions with low winds that persist for 

several days in an area that trap emissions, together with complex topography and the distance of 

the area from Arizona, we believe it is reasonable to conclude that emissions from Arizona do 

not interfere with maintenance of the 2006 24-hour PM2.5 standard at these receptors. 

 

37 ARB Almanac website (2006) http://www.arb.ca.gov/ei/maps/statemap/cntymap.htm)
22 

V.B.2. Utah 

Elevated levels of PM2.5 in the Utah nonattainment areas occur primarily in the winter months.38

The levels of elevated PM2.5 in the Salt Lake City 2006 PM2.5 nonattainment area and the 

Provo 2006 PM2.5 nonattainment area are primarily due to local emissions, as noted in the 

discussion of Salt Lake City and Provo nonattainment areas below. 

Of the 17 days with measured values above the standard in 2010 in Salt Lake City, eleven days 

were in January (with levels up to 76μg/m3), and four days were in December (with levels up to 

53μg/m3). The remaining two days above the standard were March 30 and April 27. 

During the winter months, levels of PM2.5 at background monitoring sites located north of 

Arizona and south of the Utah maintenance receptors39 are very low, generally below 3μg/m3, 

indicating that over 90% of the PM in the urban area is locally generated. As discussed above, 

this supports our finding that PM2.5 levels are not likely to be caused by regional elevated 

PM2.5 levels. The factors that indicate the elevated PM2.5 levels at these locations are caused 

by local emissions, as well as the low levels of background PM2.5 during these time periods, 

support our finding that emissions from the state of Arizona do not interfere with maintenance of 

the 2006 24-hour PM2.5 standard at these maintenance receptors. 

Box Elder, Davis, Salt Lake, Tooele, and Weber Counties (Greater Salt Lake Area)

All of Davis and Salt Lake counties, and portions of Box Elder, Tooele, and Weber counties are 

designated as part of the Salt Lake City 2006 PM2.5 nonattainment area. The SLC NAA is 

situated in a valley bordered on the east by the Stansbury Mountains,40 the Promontory 

Mountains, and the Great Salt Lake, and on the west by the Wasatch Front. During inversions, 

the NAA becomes a closed airshed (save for potential transport between the Salt Lake City and 

Provo NAAs) featuring stagnant air masses and light winds which typically oscillate back and 

forth within the airshed. As the airshed is essentially capped during inversions, PM2.5 is formed 

in-situ (and trapped) via fresh locally derived emission sources and secondary chemistry.

41

 

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Salt Lake City is 58% ammonium nitrate, 31% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

emissions from mobile, point and area sources, contribute to primary and secondarily formed 

PM2.5 that violate the standard during stable weather events associated with strong inversions. 

 

38 See Appendix E at E.1. 

39 IMPROVE monitoring network at each of six National Parks in Utah (Bryce Canyon, Zion, Capitol Reef, and 

Arches National Parks) and Nevada (Jarbidge Wilderness Area and Great Basin National Park). 

40 The Quqirrh Mountains lie between the Wasatch Front and the Stansbury Mountains. However, EPA determined 

that some area located west of the Quqirrh Mountains should still be considered part of the SLC nonattainment area. 

41 2006 24-Hour PM2.5 NAAQS Designations (74 FR 58688, November 13, 2009), Technical Support Document, 

December 2008, Index 583-669 at 40. 
23 

Utah County (Provo-Orem)

A large portion of Utah County is designated as the Provo 2006 PM2.5 nonattainment area. The 

Provo NAA is situated in the Utah Valley. Like the other low-lying valleys just west of the 

Wasatch Front, the topography of the Utah Valley makes it prone to temperature inversions. 

During inversions, the Provo NAA features stagnant air masses and calm to light winds. As the 

airshed is essentially capped, PM2.5 is formed in-situ (and trapped) via fresh locally derived 

emission sources and secondary chemistry.

42 Transport of air masses between the Salt Lake City 

and Provo NAAs can occur during inversions, as there is a 4.75-mile gap in the mountains 

separating these airsheds which is below the approximate average inversion height for these 

areas.43

Speciation data from wintertime PM2.5 exceedance days from 2004-2006 showed the average 

composition of PM2.5 in Provo is 71% ammonium nitrate, with 21% carbon and organic 

compounds, 8% ammonium sulfate, and 2% crustal. Several factors, including significant 

mobile, point, and area sources contribute to ambient levels of primary and secondarily formed 

PM2.5 that violate the standard during stable weather events associated with strong inversions. 

V.C. Transport to Eastern States 

EPA has also considered potential PM2.5 transport from Arizona emission sources to the nearest 

potential nonattainment or maintenance receptors located in the eastern, midwestern and 

southern states within the domain of the modeling analysis for the Cross State Air Pollution Rule 

(CSAPR) (76 FR 48208). The nonattainment and/or maintenance receptor nearest to Arizona 

identified in the 2012 CSAPR modeling analysis is Madison County, Illinois. The CSAPR 

modeling did not analyze the contribution of Arizona sources to Madison County, Illinois. Thus, 

EPA analyzed the magnitude of Arizona’s SO2 and NOx emissions relative to states found to 

have emissions that significantly contribute to nonattainment at that receptor. EPA also 

considered the distance of Arizona from Madison County, Illinois relative to states found to 

significantly contribute there. EPA believes that the following factors support a finding that 

emissions from Arizona sources do not interfere with maintenance of the 2006 24-hour PM2.5 

NAAQS at this receptor: (1) the relatively small magnitude of the emission inventory of PM2.5 

precursors (SO2 and NOx) in Arizona, combined with (2) the relatively long distance between 

Arizona and this receptor. EPA believes that these factors also support a finding that Arizona 

emissions do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS at any of the 

other CSAPR receptors farther east. 

In the CSAPR modeling, EPA did not quantify the PM2.5 contributions from Arizona to Illinois 

or any of the other Eastern nonattainment and maintenance receptors. However, we can make a 

qualitative conclusion about the likely contribution from Arizona to Illinois and points farther 

east by comparing the Arizona emissions to a state that was modeled in CSAPR. Texas is the 

nearest state to Arizona that was found to significantly contribute to downwind nonattainment in 

CSAPR. And in fact, Texas was found to contribute significantly to the nonattainment receptor 

in Madison County, Illinois. The 24-hour PM2.5 contribution from Texas to Madison County 

 

42 Id.

43 Id. at 41. 
24 

was above the 1% threshold (0.35 μg/m3) used in CSAPR to identify contributions that were 

considered not significant (the Texas contribution was 0.37 μg/m3). EPA has evaluated the 

relative amounts of PM2.5 precursor (SO2 and NOx) emissions in Arizona compared to the 

amounts of PM2.5 precursor emissions in Texas, as modeled in the 2012 CSAPR “base case.” 

The emission inventories used in the CSAPR modeling analyses indicate that SO2 emissions in 

Arizona are less than 10% of SO2 emissions in Texas, and NOx emissions in Arizona are less 

than 20% of NOx emissions in Texas. Specifically, the CSAPR “2012 Base Case” inventories 

provide the following statewide emissions inventory data for these two states: 274,608 tons of 

NOx and 65,046 tons of SO2 from Arizona emission sources, compared to 1,501,170 tons of 

NOx and 712,582 tons of SO2 from Texas emission sources.

44 Even though the relationship 

between upwind emissions and downwind secondary PM2.5 formation is not linear, we would 

expect the Arizona PM2.5 contribution to Illinois to be much less than that of Texas and well 

below the 1% threshold. In addition, the distance for Arizona to Illinois is approximately twice 

the distance as from Texas to Illinois. The distance from the closest part of Arizona to Madison 

County, Illinois (975 miles) is more than twice the distance to Madison County from the closest 

part of Texas (415 miles). The distance from Arizona to the other eastern receptors is even 

greater, and therefore, the expected impact somewhat smaller. Given all of these factors, EPA 

believes it is reasonable to conclude that emissions of PM2.5 and PM2.5 precursors from 

Arizona sources do not interfere with maintenance of the 2006 24-hour PM2.5 NAAQS in any 

eastern state. 

 

44 See “Emissions Inventory Final Rule TSD,” Technical Support Document (TSD) for the final Transport Rule, 

Docket ID No. EPA-HQ-OAR-2009-0491, June 28, 2011, at Tables 7-1 and 7-2.