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Enclosure 1 

SIP Completeness Checklist 

 
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STATE IMPLEMENTATION PLAN COMPLETENESS CHECKLIST 

SUBMITTAL OF STATE IMPLEMENTATION PLAN (SIP) REVISION 

2012 State Implementation Plan for the 

 Nogales PM10 Nonattainment Area 

1. SUBMITTAL LETTER FROM GOVERNOR/DESIGNEE 

 

 See cover letter. 

2. EVIDENCE OF ADOPTION 

See cover letter. 

3. STATE LEGAL AUTHORITY FOR ADOPTION/IMPLEMENTATION 

 A.R.S. §§ 49-404 and 49-406 were approved into the Arizona SIP on 6/08/2000. ADEQ's 

 Infrastructure SIP for the 1997 and 2006 PM2.5 NAAQS and the 1997 8-hour Ozone NAAQS 

 submitted to EPA Region IX on August 24, 2012, included a certified copy of authorizing statute 

 A.R.S. § 104. 

4. COMPLETE COPY OF ACTUAL REGULATION 

 Same as above. 

5. EVIDENCE THAT ARIZONA ADMINISTRATIVE PROCEDURE ACT REQUIREMENTS 

 (ARS §§ 41-1021 through 1036) WERE MET FOR RULE 

 See Appendix K. 

6 EVIDENCE OF PUBLIC HEARING PER 40 CFR 51.102 

 See Appendix K.

7 PUBLIC COMMENTS AND AGENCY RESPONSE 

 See Appendix K.

 

8. IDENTIFICATION OF POLLUTANTS REGULATED BY RULE 

 Particulate matter 10 microns and smaller in size (PM10) 

9. IDENTIFICATION OF SOURCES/ATTAINMENT STATUS 

 See Enclosure 3. 
10. WRITTEN SUMMARY OF RULE/RULE CHANGE 

 Not applicable. 

11. RULE CHANGES INDICATED BY UNDERLINING AND CROSS-OUTS 

 Not applicable. 

12. RULE’S EFFECT ON EMISSIONS 

 See Enclosure 3. 

13 DEMONSTRATION THAT NAAQS, PSD INCREMENTS AND RFP ARE PROTECTED 

 See Enclosure 3. 

14. EVIDENCE THAT EMISSIONS LIMITATIONS ARE BASED ON CONTINUOUS 

 EMISSIONS REDUCTION TECHNOLOGY 

 Not applicable. 

15. MODELING SUPPORT 

 Not applicable. 

16. IDENTIFICATION OF RULE SECTIONS CONTAINING EMISSION LIMITS, WORK 

 PRACTICE STANDARDS, AND/OR RECORD KEEPING/REPORTING REQUIREMENTS 

 Not applicable. 

17. COMPLIANCE/ENFORCEMENT STRATEGIES 

 

 See Enclosure 3. 

18 ECONOMIC TECHNICAL JUSTIFICATION FOR DEVIATION FROM EPA POLICIES 

 No known deviation from EPA policy. 
Final 

2012 State Implementation Plan 

Nogales PM10 Nonattainment Area 

August 24, 2012 

 
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iii

Executive Summary................................................................................................................................ ES-1 

Introduction 1.0 ...............................................................................................................................................1 

1.0 Physical, Demographic, and Economic Description of the Nogales NA..................................1 

 1.1 Physical, Demographic, and Economic Description of the Nogales NA...........................1 

 1.1.1 Climate and Physiography.......................................................................................1 

 1.1.2 Population .................................................................................................................2 

 1.1.3 Santa Cruz County and City of Nogales Economy................................................3 

 1.2 Nogales Regulatory Background ..........................................................................................4 

 1.2.1 EPA's Particulate Matter NAAQS ..........................................................................5 

 1.2.2 Nogales NA Statutory Boundary ...........................................................................5 

 1.2.3 General SIP Approach - Regulatory Requirements and Guidance.......................6 

2.0 Air Quality Monitoring ...................................................................................... 9 

 2.1 Monitoring Site, Equipment, and Quality Assurance Procedures.......................... 9 

 2.2 Air Quality Data..................................................................................................... 9 

 2.3 24-hour PM10 NAAQS Compliance..................................................................... 12 

3.0 Emissions Inventory........................................................................................................... 13 

 3.1 Significant Emissions Sources ............................................................................ 13 

 3.2 Nogales NA Future Year (2011) PM10 Emissions Projections.......................... 15 

4.0 Demonstration of Attainment in Accordance with Section 179B of the Clean Air Act .........16 

 4.1 Population Growth in Nogales Municipality, Sonora....................................................16 

 4.2 Nogales Municipality, Sonora, Emissions Inventories..................................................17 

 4.3 Comparison of Ambos Nogales Emissions Inventories..................................... 19 

 4.4 PM10 Exceedance Analyses - Monitoring Data, Wind Speed, and Temperature....... 19 

 Changes 

 4.5 Wind Direction and Wind Rose Analyses.......................................................... 24 

 4.6 Conceptual Model of 2007-2009 Exceedance Days .......................................... 27 

 4.7 Review of Exceedance Days Differing from 25-Day Conceptual Model.......... 29 

 4.8 Expected Exceedance Days "But For" International Transport from Mexico ... 33 

 4.8.1 Daily Analysis of Expected Exceedances ............................................. 33 

 4.8.2 Hourly Analysis of Excepted Exceedances........................................... 34 

 4.9 Conclusion ......................................................................................................... 36 

5.0 Control Measures............................................................................................................. 37 

 5.1 Definition and Selection of RACM/RACT......................................................... 37 

 5.1.2 RACM Analysis for the Nogales NA...................................................... 38 
iv

 5.2 Control Measures Adopted into the SIP and Implemented by ADEQ................. 38 

 5.2.1 Require RACT for Stack and Fugitive PM10 from Permitted................ 38 

 Stationary Sources/Require RACT for Haul Roads and Staging Areas 

 5.2.2 Require Dust Control Measures for Material Storage Piles.................... 39 

 5.2.3 Limit Use of Recreational Vehicles on Open Land ................................ 39 

 5.3 Status of 1993 Nogales NA SIP Control Measures Implemented by the City ... 40 

 5.3.1 Pave or Chemically Stabilize Unpaved Roads; Pave, Vegetate or ...................40 

 Chemically Stabilize Access Points Where Unpaved Traffic Surfaces 

 Adjoin Paved Roads 

 5.4 Control Measures Implemented by Agencies but not included in the SIP for Credit....43 

 5.4.1 General Services Administration - Reduce Idling Time of Diesel-Powered ...43 

 Vehicular Traffic at Border Entrances 

 5.4.2 Provide for Storm Water Drainage to Prevent Water Erosion onto Paved ......43 

 Unpaved Roads/Provide for Traffic Rerouting or Rapid Clean Up of 

 Temporary Sources of Dust on Paved Roads 

 5.4.3 Require Permanent Unpaved Haul Roads, and Parking or Staging Areas.......44 

 at Commercial 

 5.4.4 Require Haul Trucks to be Covered...................................................................44 

 5.5 Nogales NA RACM/RACT Conclusion..........................................................................44 

6.0 Reasonable Further Progress and Contingency Measures......................................................46 

7.0 Transportation Conformity Procedures and Motor Vehicle Emissions Budget .................47 

8.0 Conclusions and Summary............................................................................................................49 

List of Figures 

Figure ES1 – Map of Nogales NA .......................................................................................... ...ES-2 

Figure ES2 – Nogales Post Office Filter-Based Monitor PM10 Monitoring Data.......................ES-3 

 Trends 1985-2010 

Figure ES3 – Nogales Post Office BAM Monitoring Data Trends 2005-2010 ......................... ES-3 

 Monitoring Trends 2005-2010 

Figure ES4 – 2008 Annual Emissions Inventory for the Nogales, Arizona, PM10 ................... ES-4

 Nonattainment Area 

Figure 2.1 – Nogales Post Office Filter-Based Monitor PM10 Monitoring Data Trends 1985-2010 .....12 

Figure 2.2 – Nogales BAM Monitor PM10 Monitoring Data Trends 2005-2010 .....................................12 
v

List of Figures Continued 

Figure 3.1 – 2008 Annual Emissions Inventory for the Nogales, Arizona PM10 Nonattainment Area.....13 

Figure 4.1 – Comparison of Ambos Nogales Population Growth 1995-2010............................................17 

Figure 4.2 – Nogales, Sonora 2008 High and Low Inventories Compared to Nogales, AZ 2008 ............19

 Inventory 

Figure 4.3 – PM10 Exceedances at the Nogales, Arizona Post Office, by Month and Year ......................20 

Figure 4.4 – Hourly Ambient PM10 Concentrations on 29 Exceedance Dates ...........................................21 

Figure 4.5 – Hourly Ambient PM10 Concentrations on 26 Similar Exceedance Days, .................22 

 Excluding the Following Days: January 1, 2007; May 22, 2008; and 

 January 1, 2009

Figure 4.6 – Hourly Wind Speed Variations on 29 Exceedance Dates.......................................................23 

Figure 4.7 – Hourly Temperature Variations on 29 Exceedance Days ......................................................24 

Figure 4.8 – Wind Rose of Wind Speed vs. Wind Direction at the Nogales, Arizona, Post......................25 

 Office BAM Monitor for all 29 Exceedance Days 

Figure 4.9 – Pollution Rose of PM10 Concentration vs. Wind Direction at the Nogales ....................26 

 Arizona Post Office BAM for all 29 Exceedance Days 

Figure 4.10 – Average Hourly PM10 Concentration, Wind Speed, and Temperature at the Nogales, ..........28 

 Arizona Post Office BAM vs. Time of Day for all Exceedances Excluding January 1, 

 2007, May 22, 2008, and January 1, 2009 

Figure 4.11 – January 1, 2007 PM10 Concentrations and Wind Speeds Compared to 26................. 30 

 Exceedance Day Average PM10 Concentrations and Wind Speeds from Figure 4.11 

Figure 4.12 – January 1, 2009 PM10 Concentrations and Wind Speeds Compared to 26................. 31 

 Exceedance Day Average PM10 Concentrations and Wind Speeds from Figure 

Figure 4.13 – May 22, 2008 PM10 Concentrations and Wind Speeds Compared to 26 Exceedance................ 32 

 Day Average PM10 Concentrations and Wind Speeds from Figure 4.10 

Figure 4.14 – January 26, 2008 PM10 Concentrations and Wind Speed Compared Average ....................32 

 PM10 Concentrations and Wind Speeds from Figure 4.11 

Figure 5.1 – Image of an Intersection of Paved and Unpaved Road in Rio Rico .................................42 

Figure 8.1 – Comparison of Ambos Nogales Population Growth 1995-2010 ......................................49 

List of Tables 

Table ES-1 – Arizona Administrative Code Rules Approved into the Arizona SIP...............ES-5 

Table 1.1 – Climatological Data for Nogales, AZ (1952-2010) ..................................................... 2 

Table 1.2 – Population of Nogales, Rio Rico, and Santa Cruz County 1990-2010 ......................... 2 

Table 1.3 – Population Projections for the Region .......................................................................... 3 

Table 1.4 – Population of Nogales Municipality, Sonora, Mexico.................................................. 3 
vi

List of Tables Continued 

Table 1.5 – Building Permits Issued in Nogales and Santa Cruz County 1990-2010...................... 4 

Table 1.6 – Clean Air Act (CAA) Regulatory Requirements .......................................................... 7 

Table 2.1 – Nogales Post Office Monitor Site Specifications.......................................................... 9 

Table 2.2 – Nogales Filter-Based 24-hour PM10 Monitoring Data 1985-2010.............................. 10 

Table 2.3 – Nogales Continuously Operating BAM Monitor PM10 Monitoring Data 2005-2010 ..........11 

Table 3.1 – Significant PM10 Emissions Sources in the Nogales NA ........................................... 14 

Table 3.2 – PM10 Emissions Sources in the Nogales NA .............................................................. 14 

Table 3.3 – Projected PM10 Emissions 2008 and 2011 .................................................................. 15 

Table 4.1 – 2008 and 2011 PM10 Emissions Inventories for Nogales, Sonora .............................. 18 

Table 4.2 – 24-hour Concentration and Hourly Concentrations Disaggregated by ....................... 33 

 Southerly Wind Direction Quadrant for Exceedance Days Differing from 

 Conceptual Model 

Table 5.1 – Arizona Administrative Code Rules Approved into the Arizona SIP for PM10 Sources .....37 

Table 5.2 – PM10 Generating Point Sources Operating in the Nogales NA in 2008...................... 39 

Table 5.3 – Calculated PM10 Emissions Assuming Paved Road Efficiency for Roads in ............. 41 

 the City of Nogales, Arizona 1993-1996 

Table 5.4 – Calculated PM10 Emissions Assuming Paved Road Efficiency for Roads in........................42 

 Rio Rico within the Nogales NA 

Table 7.1 – 2011 Nogales NA Motor Vehicle Emissions Budget .......................................................48 

List of Appendices 

Appendix A – Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona 

 PM10 Nonattainment Area 

Appendix B – 2008 & 2011 PM10 Emissions Inventories for the Nogales Nonattainment Area, 

 Santa Cruz County, Arizona 

Appendix C – 2008 and 2011 PM10 Emissions Inventories, Nogales Municipality, State of 

 Sonora, Mexico 

Appendix D – Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in 

 Nogales, Arizona: 2007-2009 

Appendix E – ADEQ Technical Support Document for Control Measure Emission Reductions 

Appendix F – Correspondence 

Appendix G – Supplementary Information 

Appendix H – NNA Monitoring Data 2008-2010 

Appendix I – 1996 Reasonable Further Progress Report 

Appendix J – Potential New Source 

Appendix K – Public Process Documentation 
7

EXECUTIVE SUMMARY 

 The Nogales PM10 Nonattainment Area (Nogales NA) is located 66 miles south of Tucson, 

covering approximately 76 square miles along the international border with Mexico in Santa Cruz 

County. The City of Nogales and portions of Rio Rico, an unincorporated community, occupy most of the 

nonattainment area, as depicted in Figure ES-1. Nogales, Arizona and Nogales, Sonora, Mexico, 

collectively referred to as Ambos Nogales, form a micropolitan area bisected by the international border. 

 Pursuant to the 1990 Clean Air Act (CAA) Amendments, by operation of law all areas where 

violations of the PM10 NAAQS had been recorded were designated as moderate nonattainment areas for 

PM10, including the Nogales NA. Because Arizona did not submit a required moderate PM10 plan for the 

Nogales NA by the November 15, 1991, deadline, EPA issued a finding of failure to submit (57 FR 

19906; May 8, 1992). The Arizona Department of Environmental Quality (ADEQ) subsequently 

submitted a State Implementation Plan (SIP) for the Nogales NA on June 14, 1993.1

 EPA found the SIP 

to be complete but did not take action on it.2 One of the purposes of this document is to ultimately serve 

as a replacement of the 1993 Nogales NA SIP. This plan demonstrates that the annual expected 

exceedances are less than one but for emissions originating in Mexico. 

 This PM10 SIP for the Nogales NA is organized as follows and is intended to meet the 

requirements established by the CAA for moderate PM10 nonattainment area plans. 

 Chapter 1 provides an overview of the Nogales NA and Santa Cruz County. It discusses the 

climate, physiography, population, and economy of the area and the impact each has on ambient PM10

concentrations. Chapter 1 also includes an account of the regulatory history of the PM10 NAAQS and the 

Nogales NA, and describes how this SIP meets all the regulatory requirements for a PM10 nonattainment 

area plans under CAA Sections 172, 189, and 179B. 

 

1

 “Final State Implementation Plan for the Nogales PM10 Nonattainment Area.” ADEQ. Submitted to EPA June 14, 1993. 

<http://www.azdeq.gov/environ/air/plan/download/nogpm10sip_061993.pdf> 2

 Correspondence. Letter from EPA to ADEQ dated November 30, 1993. See Appendix F.4. 

ES-1 
8

Figure ES-1 

ES-2 ES- 
9

 Chapter 2 describes how the Nogales NA ambient monitoring network meets CAA and EPA 

regulatory requirements, provides a description of the monitoring equipment, and includes a physical 

description of the monitor sites. This chapter provides PM10 monitoring data collected by monitors in the 

Nogales NA from 1985-2010. As shown in Figure ES-2, filter-based monitoring data from 2008-2010 

showed observed concentrations below the PM10 NAAQS. Additional data collected during 2008-2010 at a 

co-located continuous monitor, however, showed observed concentrations above the NAAQS, as shown in 

Figure ES-3.3

 Although recent trends indicate a decline in ambient concentrations, based on preliminary 

monitoring data, the Nogales BAM monitor recorded exceedances in 2011; quality assured monitoring data 

for the Nogales NA will be certified and submitted to EPA in 2012. 

Figure ES-2 

Nogales Post Office Filter-Based PM10 Monitoring Data Trends 1985-2010

0

50

100

150

200

250

300

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

ug/m3

24hr Max 2nd 24hr High PM10 NAAQS

Source: EPA's AQS Database. 

Figure ES-3 

Nogales BAM Monitoring Data Trends 2005-2010

0

50

100

150

200

250

300

350

400

2005 2006 2007 2008 2009 2010

ug/m3

1st Hi 2nd Hi 3rd Hi 4th Hi PM10 NAAQS

 Source: Ibid. 

 

3

 Due to data completeness deficiencies in 2010 BAM monitoring data, ADEQ reviewed, certified, and quality assured 

data for 2007-2009 collected by the Nogales BAM monitor and determined the Nogales NA did not meet the NAAQS 

during that period either. 

ES-3 
10

 Chapter 3 contains the 2008 base year PM10 emissions inventory; provides a summary of the 

inventory methodology; and identifies significant and insignificant emission sources in the Nogales NA. 

Figure ES-4 depicts the 2008 emissions inventory major source categories. Chapter 3 also includes a 

projected emissions inventory for 2011. 

Figure 3.1

2008 Annual Emissions Inventory for the Nogales, Arizona 

PM10 Nonattainment Area

1,531 tons per year total

Other

87 tpy

6%

Residential 

Garbage Burning 

24 tpy

 2%

Residential 

Construction 

24 tpy

2%

Residential Wood 

Burning

24 tpy

 2% Paved Road Dust 

121 tpy

 8%

Commercial/

Industrial 

Construction

 143 tpy

9%

Road 

Construction

267 tpy

17%

Unpaved Road 

Dust 

865 tpy

 57%

Source: 2008 and 2011 PM10 Emissions Inventories for the Nogales NA, Santa Cruz County, 

Arizona (see Appendix B). Estimates rounded. 

 Chapter 4 includes a demonstration in accordance with CAA section 179B that but for emissions from 

Mexico, the Nogales NA would attain the PM10 standard. The demonstration includes analyses of population 

growth, sources of PM10, ambient PM10 concentrations, and meteorology in the Ambos Nogales area. 

 Chapter 5 describes CAA requirements for reasonably available control measures (RACM) in 

moderate PM10 nonattainment areas. The chapter cites applicable State laws already approved into the 

Arizona SIP. Chapter 5 describes the selection process, implementation, and status of RACM required by 

the SIP submitted for the Nogales NA in 1993 and describes in detail the extensive road paving projects 

that have been completed since that time. This chapter includes a demonstration that the control measures 

meet CAA criteria to qualify as RACM and also includes supplemental control measures not intended for 

inclusion in the Arizona SIP. 

 

 Chapter 6 discusses CAA requirements for contingency measures that provide supplementary 

emissions reductions not included in a SIP attainment demonstration in the event of failure to make RFP 

or attainment by the prescribed attainment date. 

ES-4 
11

 Chapter 7 discusses requirements in the CAA to ensure potential emissions from federally funded 

transportation projects will not delay attainment of the standard in the Nogales NA or cause violations of 

the PM10 standards. To meet this obligation, the Transportation Conformity Rule (40 CFR Part 93) directs 

the State to establish a limit or “budget” for onroad emissions in the area. The emissions budget 

developed for this SIP assists in assuring transportation conformity requirements are met. Each new travel 

plan must be shown to conform with the motor vehicle emissions budget (MVEB) at least every four 

years and upon any amendments, including a new regional emissions analysis. 

 Chapter 8 summarizes the obligations and commitments the State is making with the submission 

of this SIP. Several of the applicable air quality sections of Arizona Revised Statutes have been amended 

and the numbering system has changed since the rules listed below in Table ES-1 were approved into the 

State Implementation Plan. The following rules have been submitted to EPA and approved into the 

Arizona SIP. 

 

4

 R18-2-702, General Provisions, reflects the current R18 Arizona Administrative Code numbering format. The R9 

series of rules were subsequently renumbered as well, but have only been approved by EPA in the original 

numbering format. 

Table ES-1

Arizona Administrative Code Rules Approved into the Arizona SIP

Rule FR Date FR Citation

R9-3-404 Open Areas, Dry Washes, or Riverbeds 4/23/1982 47 FR 17485

R9-3-405 Roadways and Streets 4/23/1982 47 FR 17485

R9-3-406 Material Handling 4/23/1982 47 FR 17485

R9-3-407 Storage Piles 4/23/1982 47 FR 17485

R9-3-410 Evaluation of Nonpoint Source Emissions 4/23/1982 47 FR 17485

R9-3-502 Standards of Performance for Unclassified Sources 10/19/1984 49 FR 41026

R9-3-522 Standards of Performance for Existing Gravel and 

Stone Crushing Operations 

9/28/1982 47 FR 42572

R18-2-7024 General Provisions 8/24/2004 69 FR 51952 

 

ES-5
1

1.0 INTRODUCTION 

 Chapter 1 provides a description and regulatory history of the Nogales Nonattainment Area (NA) 

and presents general regulatory requirements for PM10 nonattainment areas.

1.1 Physical, Demographic, and Economic Description of the Nogales NA 

 Section 1.1.1 describes the climate and physiography of the Nogales NA; Sections 1.1.2 and 1.1.3 

provide an overview of the demographics and economy of the Nogales area. 

1.1.1 Climate and Physiography 

 The Nogales NA is located on the U.S./Mexico border 66 miles southeast of Tucson. This region of 

the Sonoran Desert is characterized by north-south elongated valleys surrounded by mountain ranges. Nogales 

is located in a valley created by the Nogales Wash, a tributary of the nearby Santa Cruz River. 

 The mean elevation in Nogales, Arizona is 3,865 feet above sea level. Mountain ranges near 

Nogales include the Patagonia Mountains to the east and the Tumacacori, Atascosa, and Pajarito 

mountains to the west. Approximately twenty-five miles to the north are the Santa Rita Mountains and 

Madera Canyon in the Coronado National Forest where Mount Wrightson rises to an elevation of 9,432 

feet. Northwest of Interstate 19 are the Cerro Colorado, Las Guijas, and Sierrita Mountain Ranges. 

 The mean elevation in Nogales, Sonora is 4,265 feet above sea level.5

 At 5,380 feet, the highest 

elevation in Nogales, Sonora is the Cerro de los Nogales (Nogales Hill), west of where the Obregón and 

Colosio routes meet, near the southern end of the city. 

 The elevation drops approximately 709 feet from the southernmost edge of the Nogales, Sonora 

urban boundary to the Nogales NA northern boundary line. 

 The average daily maximum temperature is 79.7 oF, based on a 62-year average of meteorological 

data (see Table 1.1). The highest monthly daily maximum average temperature (94.1 oF.) occurs in July, 

and the lowest monthly daily minimum average temperature (64.3 oF.) occurs in January. 

 The yearly average total rainfall for the Nogales area is 17.21 inches, as shown in Table 1.1. The 

majority of this precipitation falls in July and August, when warm moist air penetrates Arizona from the 

Gulf of Mexico. The area receives approximately 8.5 inches of precipitation during this time. The area 

receives an average of only 0.22 inches of rain in May, the driest month of the year. 

 

5

 “Statistical Municipal Workbook for Nogales, Sonora,” 2005 edition, INEGI. <http://www.inegi.org.mx/> 
2

Table 1.1 

Climatological Data for Nogales, AZ (1952-2010) 

Average Temperature oF Rain in 

Inches 

Month Daily Max. Daily Min. Avg. Total 

January 64.3 27.3 1.14

February 66.7 29.6 0.86

March 70.7 33.7 0.87

April 78.1 38.6 0.38

May 86.3 45.0 0.22

June 95.3 54.5 0.46

July 94.1 63.9 4.38

August 91.7 62.7 4.03

September 90.2 55.5 1.57

October 82.4 43.9 1.29

November 71.7 33.0 .065

December 64.6 27.6 1.37

Annual Average 79.7 43.0 17.21

SOURCE: Western Regional Climate Center.6

1.1.2 Population 

 Table 1.2 includes historical and projected population estimates for the Nogales area. Estimates for 

1990, 2000, 2008, and 2010 were obtained from the U.S. Census Bureau. The base year for the emissions 

inventory is 2008. According to 2008 population estimates, 55 percent of the County’s population resides 

within the Nogales NA, which includes portions of Rio Rico and all of the City of Nogales. The Arizona 

Commerce Authority (ACA) population projections, shown in Table 1.3, were developed in 2006 based on the 

rate of growth during the peak of the housing market. Updated projections from the ACA based on 2010 

Census data will not be published until December 31, 2012. 

Table 1.2

Population of Nogales, Rio Rico, and Santa Cruz County 1990-2010

1990 2000 2008 2010

City of Nogales 19,489 20,878 19,752 20,837

Santa Cruz County 29,676 38,381 43,091 43,716

Portions of Rio Rico SE 

and SW in Nogales NA

3,983 4,042

 Source: U.S. Census Bureau. Rio Rico population figures were estimated from U.S. 

 Census data; see Appendix B for allocation calculations.

 

6

 “Nogales, Arizona.” Western Regional Climate Center. n.d. June 28, 2011. 

< http://www.wrcc.dri.edu/cgi-bin/cliMAIN.pl?az5924>. 
3

 

Source: Arizona Commerce Authority. 

 Nogales, Sonora, depicted in Figure ES-1, is Nogales, Arizona’s much larger sister city. The Nogales 

Municipality's population in 2010 is estimated to be 220,292.7

 Table 1.4 contains population estimates and 

projections obtained from Mexico’s Instituto Nacional de Estadistica y Geografía (INEGI). 

Table 1.4

Population of Nogales Municipality, Sonora, Mexico

1995 2000 2005 2010

Nogales Municipality, Sonora 133,491 159,787 193,517 220,292 

Source: INEGI. 

1.1.3 Santa Cruz County and City of Nogales Economy 

 The City of Nogales was founded in 1880 when a trading post opened on the international border; 

two years later, a railway running through Nogales connected the U.S. and Mexico. Today the economies 

of Nogales, Arizona, and Nogales, Sonora are largely interdependent. According to the ACA, 47 percent 

of Santa Cruz County’s annual sales tax revenue is generated from purchases made by residents of 

Mexico.8

 There are two ports of entry (POE) in the area, the DeConcini POE in downtown Nogales and 

the Mariposa POE 0.5 mile to the west. The DeConcini POE does not accept commercial trucks, all of 

which are required to cross the border at the Mariposa POE. From November through April, 

approximately 136,000 trucks haul produce from Mexico to warehouses in Nogales; approximately 

200,000 U.S. trucks distribute the fresh produce to supermarkets in the United States and Canada.7

 The 

Nogales ports of entry serve as the gateway to 50 percent of all fresh fruits and vegetables shipped into 

the U.S. from Mexico.8

 

 In 2008, 74 percent of Nogales Arizona's working population was employed in the private sector. 

The trade, transportation, and utilities industry accounted for 43 percent of all employment; 26 percent of 

the working population was employed in the public sector, with most working for the Department of 

Homeland Security, Santa Cruz County, the City of Nogales, and Cochise Community College. The 

County’s unemployment rate was 13.1 percent in 2009, 9 higher than the State average, 10.6 percent. 

 

7 Instituto Nacional de Estadistica y Geografia. n.d. June 1, 2011. <http://www.inegi.org.mx/>. 8

 “Nogales Community Profile.” Arizona Department of Commerce. September 10, 2009. June 1, 2011. 

<http://www.nogalesusa.com/commerce.html> 9

 Census Bureau. Santa Cruz County, AZ Census Statistics. 

 <http://census-statistics.findthedata.org/l/111/Santa-Cruz-County-AZ> 

Table 1.3 

Population Projections for the Region

2020 2030

 City of Nogales 24,783 26,356

 Santa Cruz County 61,658 71,033
4

 The number of building permits in the City of Nogales has slowed considerably since 2000; the 

number of building permits issued in 2010 was 5, compared to 60 in 2000, as shown in Table 1.5. Home 

sales in the third quarter of 2011 were 74 percent lower than the market’s peak in the first quarter of 2006.10 

Table 1.5 

Building Permits Issued in Nogales and Santa Cruz County 1990-2010 

1990 1996 2000 2010

City of Nogales n/a 37 60 5

Unincorporated Santa Cruz County n/a 265 301 47

Santa Cruz County 217 306 302 53

Source: U.S. Census Bureau.11

1.2 Nogales NA Regulatory Background 

 EPA promulgated a revised particulate matter NAAQS in 1987 (52 FR 24634; July 1, 1987). 

These primary and secondary standards apply to particulate matter 10 microns12 or less in diameter 

(PM10) and superseded the previous total suspended particulate (TSP) standards. ADEQ began monitoring 

PM10 in the Nogales NA in 1985. 

 

As part of the implementation policy for the 1987 PM10 NAAQS, EPA created a tiered scale to 

designate nonattainment areas based on an area’s probability of violating the standard. An area with a high 

probability of violating the standard was designated as a Group I area; an area with a moderate probability of 

violating was designated as a Group II area; and an area likely to attain the standard was designated as a Group 

III area. The Nogales planning area was subsequently classified as a Group II Area, with a moderate likelihood 

of violating the PM10 NAAQS. In accordance with Section 110 (a)(1) of the Clean Air Act (CAA), the State 

was required to submit a State Implementation Plan (SIP) within three years after promulgation of the NAAQS 

(52 FR 24672; July 1, 1987, and 52 FR 29383; August 7, 1987) by August 7, 1990. 

 With the CAA amendments of 1990, areas where previous violations of the PM10 standard had 

been recorded prior to January 1, 1989, were designated nonattainment for PM10 by operation of law and 

classified as “moderate”; these areas included all former Group II PM10 planning areas like the Nogales 

NA (55 FR 45799; October 31, 1990). On March 15, 1991, EPA published a list of the areas designated 

nonattainment for PM10 upon enactment of the 1990 amendments, including the Nogales nonattainment 

area (56 FR 11101; March 15, 1991). Later, EPA codified the PM10 nonattainment designations and 

moderate area classifications (56 FR 56694; November 6, 1991). 

 As stipulated in the 1990 amendments, by November 15, 1991, Arizona was required to submit a 

SIP for the Nogales NA demonstrating attainment of the PM10 NAAQS by December 31, 1994. Because 

 

10 Citydata.com. <http://www.city-data.com/zips/85621.html> 11 U.S. Census Bureau. Web. <http://censtats.census.gov/bldg/bldgprmt.shtml?> 12 One micron is one millionth of a meter, or 0.0004 inches. 
5

Arizona did not submit a SIP for the Nogales NA by the November 15, 1991 deadline, EPA made a finding 

of failure to submit a PM10 SIP on December 16, 1991. In response, on June 14, 1993, Arizona submitted 

the ‘‘Final State Implementation Plan for the Nogales PM10 Nonattainment Area.” (1993 Nogales NA SIP) 

EPA found the plan to be complete by letter dated November 30, 1993, but did not act on the plan.13

 On January 11, 2011, EPA promulgated a determination of attainment as of the applicable 

attainment date for the Nogales NA based on ambient air quality monitoring data from 1992-1994, 

retroactively affirming that the area had met the PM10 NAAQS by the December 31, 1994 deadline 

established by the 1990 amendments of the CAA (76 FR 1532; January 11, 2011). 

1.2.1 EPA’s Particulate Matter NAAQS 

The CAA requires the EPA to assess the latest scientific information and review the particulate 

matter NAAQS every five years. On October 17, 2006, EPA revised the 1987 PM10 standards by retaining 

the existing 24-hour PM10 standard and revoking the annual PM10 standard effective December 18, 2006 

(71 FR 61144; October 17, 2006). Therefore, this SIP revision addresses EPA’s current primary and 

secondary 24-hour PM10 NAAQS. The PM10 NAAQS allows for a maximum 24-hour average of 150 

μg/m3

. The 24-hour standard is attained when the expected number of days per calendar year with a 24-

hour average concentration exceeding the standard is less than or equal to one (see 40 CFR 50.6 and 40 

CFR Part 50, Appendix K). The primary standard was established to protect human health; the secondary 

standard was established to protect property, materials, and general welfare. Both NAAQS have a 24-hour 

average concentration limit of 150 μg/m3

. This plan addresses both the primary and secondary PM10

NAAQS. 

1.2.2 Nogales Nonattainment Area Statutory Boundary 

 The Nogales NA in southern Arizona is within Santa Cruz County on the international border 

with Mexico, and includes the City of Nogales, portions of the Rio Rico community, and unincorporated 

portions of the County. It is shown in Figures ES-1. The nonattainment area is codified at 40 CFR 81.303 

and is described by the townships and ranges listed below that are within the State of Arizona and lie east 

of 111 degrees longitude: 

T23S, R13E 

T23S, R14E 

T24S, R13E 

T24S, R14E 

 

13 Correspondence. Letter from EPA to ADEQ dated November 30, 1993. See Appendix F.4. 
6

1.2.3 General SIP Approach – Regulatory Requirements and Guidance 

 The November 1990 CAA amendments were enacted by the United States Congress to improve air 

quality across the nation. One of the primary goals of this comprehensive revision to the CAA was to 

expand and clarify the planning provisions for those areas not currently meeting the NAAQS. The 

amendments identify specific emission reduction goals, require both a demonstration of reasonable further 

progress (RFP) and attainment, and incorporate more stringent sanctions for failure to attain or to meet 

interim milestones. Title I, Part A, and Title I Part D, Subparts 1 and 4 of the CAA are applicable to this 

SIP. Table 1.6 includes the SIP requirements and explains how this document meets them. The pollutant 

specific requirements for moderate PM10 nonattainment areas applied to the U.S. are found in section 189 of 

the CAA, and the general planning and control requirements for nonattainment area plans are found in CAA 

sections 110 and 172. The following excerpt from the CAA describes requirements of SIPs submitted for 

consideration under Section 179B - International Border Areas: 

Sec. 179B. INTERNATIONAL BORDER AREAS 

 "(a) IMPLEMENTATION PLANS AND REVISIONS. — Notwithstanding any other 

 provision of law, an implementation plan or plan revision required under this chapter shall 

 be approved by the Administrator if— 

 (1) such plan or revision meets all the requirements applicable to it under the Act other than 

 a requirement that such plan or revision demonstrate attainment and maintenance of the relevant 

 national ambient air quality standards by the attainment date specified under the 

 applicable provision of this Act, or in a regulation promulgated under such provision, and 

 (2) the submitting State establishes to the satisfaction of the Administrator that the implementation plan 

 of such State would be adequate to attain and maintain the relevant national ambient air quality 

 standards by the attainment date specified under the applicable provision of this chapter, or in a 

 regulation promulgated under such provision, but for emissions emanating from outside of the United 

 States... 

(d) ATTAINMENT OF PM10 LEVELS - Notwithstanding any other provision of law, any State that 

 establishes to the satisfaction of the Administrator that, with respect to a PM10 nonattainment area in 

 such State, such State would have attained the national ambient air quality standard for carbon 

 monoxide [sic] by the applicable attainment date, but for emissions emanating from outside the 

 United States, shall not be subject to the provisions of section 188 (b)(2)." 14 

EPA issued administrative guidance in 1994 setting forth several types of information that could 

be used to evaluate the impact of emissions emanating from outside the U.S. and demonstrate that a 

 

14 Carbon monoxide is an apparent typographical error; the text should read "PM10". 
7

border area's inability to meet the NAAQS was due to emissions from outside the U.S.15 Section 4.0 

follows these guidelines to demonstrate that the Nogales NA would be in attainment of the 24-hour PM10

NAAQS "but for" emissions from Mexico. 

Table 1.6 

 Clean Air Act (CAA) Regulatory Requirements

CAA 

Citation Action to Meet Requirement Location in Document

CAA Section 172(c), Nonattainment Plan Provisions 

172(c)(1) 

General 

“...Such plan provisions shall provide for the implementation of all 

reasonably available control measures (RACM) as expeditiously as 

practicable [including such reductions in emissions from existing sources in 

the area as may be obtained through the adoption, at a minimum, of 

reasonably available control technology (RACT)] and shall provide for 

attainment of the national primary ambient air quality standards...” 

Chapter 5.0 provides 

an explanation of 

RACM/RACT for 

PM10 sources in the 

Nogales NA. 

172(c)(2) 

Reasonable 

Further 

Progress 

Plan provisions shall demonstrate RFP or “annual incremental reductions in 

emissions...for the purpose of ensuring attainment of the applicable national 

ambient air quality standards by the applicable date.” 

In Chapter 4.0, the 

State demonstrates 

that the Nogales NA 

would be in 

attainment but for 

emissions from 

Nogales, Sonora and 

that RFP is not 

required. 

172(c)(3) 

Emissions 

Inventory

The plan provisions “...shall include a comprehensive, accurate, current 

inventory of actual emissions from all sources of the relevant pollutant(s)...” 

Base-year PM10 

emission estimates 

are presented in 

Chapter 3.0. 

172(c)(5) 

Permits for 

New and 

Modified 

Major 

Stationary 

Sources

The plan provisions “...shall require permits for the construction and 

operation of new or modified major stationary sources anywhere in the 

nonattainment area...” 

All new sources and modifications to existing sources in Arizona are subject 

to state requirements for preconstruction review and permitting pursuant to 

AAC, Title 18, Chapter 2, Articles 3 and 4. All new major sources and 

major modifications to existing major sources in Arizona are subject to the 

New Source Review (NSR) provisions of these rules or Prevention of 

Significant Deterioration (PSD) for maintenance areas. 

Table 5.2 in Chapter 

5.0 lists permitted 

sources in the Nogales 

NA. 

 

15 State Implementation Plans for Serious PM10 Nonattainment Areas, and Attainment Date Waivers for PM10 Nonattainment 

Areas Generally; Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990

(59 FR 41,998; August 16, 1994). 
8

Table 1.6 

 Clean Air Act (CAA) Regulatory Requirements

CAA 

Citation Action to Meet Requirement Location in Document

CAA Section 172(c), Nonattainment Plan Provisions 

172(c)(6) 

Other 

Measures

The plan “...shall include enforceable emissions limitations, and such other 

control measures, means or techniques....as well as schedules and 

timetables for compliance, as may be necessary or appropriate to provide for 

attainment of such standard in such area by the applicable attainment date...” 

Emissions limitations 

and control measures 

for sources in the 

Nogales NA are 

described in Chapter 

5.0. 

172(c)(7) 

Compliance 

with Section 

110(a)(2), 

Implementati

on Plans 

The plan provisions “... shall also meet the applicable provisions of Section 

110(a)(2).” 

The requirements 

of Section 110(a)(2) 

are detailed elsewhere 

in this table. 

172(c)(8) 

Equivalent 

Techniques

The plan may include upon application by the state “... the use of equivalent 

modeling, emission inventory, and planning procedures ...” as allowed by 

the administrator. 

Chapter 4.0 includes 

an analysis 

demonstrating but for 

emissions from 

Mexico, the Nogales 

NA would meet the 

PM10 standard. 

172(c)(9) 

Contingency 

Measures

The plan “... shall provide for the implementation of specific measures to be 

undertaken if the area fails to make RFP or to attain the national primary 

ambient air quality standard ... Such measures shall be included in the plan 

revision as contingency measures to take effect in any such case without 

further action by the State or the Administrator.” 

Chapter 6.0 describes 

the State’s 

contingency plan. 

CAA Section 110(a)(2) – Implementation Plans

110(a)(2)(A) 

Control 

Measures 

and 

Emission 

Limits 

Section 110(a)(2)(A) requires that states provide for enforceable emission 

limitations and other control measures, means, or techniques, as well as 

schedules for compliance necessary to meet applicable requirements of 

CAA. 

Chapter 5.0 describes 

the measures 

implemented to 

reduce PM10

emissions and ensure 

future maintenance of 

the NAAQS. 

CAA Section 179B – International Border Areas 

179B 

International 

Border 

Areas 

Section 179B of the CAA provides the State with an option to demonstrate 

that a nonattainment area would meet the NAAQS but for emissions 

emanating from outside of the United States. 

Chapter 4.0 

demonstrates the 

Nogales NA would 

be in attainment but 

for emissions from 

Mexico. 
9

2.0 AIR QUALITY MONITORING 

 

 The primary goal of PM10 monitoring in the Nogales Nonattainment Area (NA) is to collect the 

data necessary to determine compliance with the PM10 NAAQS and fulfill the regulatory requirements for 

PM10 monitoring in the nonattainment area. This chapter provides a general description of the Nogales 

NA monitoring network and historical PM10 air quality data for the years 1985 through 2010. 

2.1 Monitoring Site, Equipment, and Quality Assurance Procedures 

 The Nogales NA monitors were installed and are maintained in accordance with federal siting and 

design criteria16 and consistent with ADEQ’s State of Arizona Air Monitoring Network Plan for the Year 

2011, which was approved by EPA on December 1, 2011.17 Presently ADEQ operates two PM10 monitors at 

the Nogales Post Office site in the center of the Nogales business district. ADEQ has operated a filter-based 

monitor at that location since 1985 that operates on a one-in-six day schedule. A single exceedance recorded 

by a monitor operating on this schedule counts as six exceedances and the area is in nonattainment of the 

PM10 NAAQS. A continuously operating Beta Attenuation Monitor (BAM) has been operating at the Post 

Office site since February 2004. ADEQ began operating a weather station at the site in June 2003.

 

 The monitor site was selected in an effort to monitor the maximum PM10 impacts on the Nogales 

population. The PM10 monitors are middle-scale monitors suited to measure concentrations within a 1/3 of 

a mile radius (40 CFR 58, Appendix D). Table 2.1 features the locations, methods, and parameters 

measured at the site.

Table 2.1 

Nogales Post Office Monitor Site Specifications 

AQS ID 

Number 

Latitude Longitude Device 

Types 

Pollutants 

Measured 

Address Scale Objective 

04-023- 

0004 

31.3372 -110.936 Partisol 

and BAM 

PM10, PM2.5, 

Meteorology 

300 N. 

Morley 

Ave 

Neighborhood Population 

Source: State of Arizona Air Monitoring Network Plan for the Year 2011. 

2.2 Air Quality Data 

 Monitoring for PM10 began within the Nogales NA in 1985. Since 1985, numerous exceedances 

of the 24-hour PM10 standard of 150 μg/m3

 have been recorded, with 24-hour average ambient PM10 

values that exceed the standard ranging from 155 to 351 μg/m3. Following the implementation of the 

control measures included in the 1993 Nogales NA SIP, a reduction was evident in both the maximum 

and second-highest 24-hour PM10 concentrations. The Nogales NA met the PM10 NAAQS by the 

 

16 40 CFR Part 58, Appendices D and E.

17 Correspondence. Letter from EPA to ADEQ dated December 1, 2011. See Appendix F.1. 
10

December 31, 1994, deadline established by the 1990 CAA Amendments (76 FR 1532; January 11, 

2011). The Nogales NA continued to meet the NAAQS until 1998. 

 Since that time, intermittent exceedances have been recorded by the filter-based and continuously 

operating monitors. Although there were no exceedances recorded by the filter-based monitor in 2009-

2010, preliminary data indicate the filter monitor did violate in 2011. The BAM monitor did record six 

exceedances in 2010; however, the BAM monitor experienced significant technical malfunctions during 

2010 resulting in four calendar quarters with incomplete data. Preliminary data for 2011 indicate 

exceedances were recorded. Quality assured and certified data for 2011 will be submitted to EPA in 2012. 

 

 Table 2.2 displays the maximum 24-hour values recorded by the filter-based PM10 monitor from 

1985-2010, and Table 2.3 displays the maximum 24-hour values recorded by the continuously operating 

BAM monitor from 2005-2010.18 Appendix H contains data for each quarter in the most recent three-year 

period during which quality-assured data is available, 2008-2010. To be in compliance with the NAAQS, 

the area can not exceed the standard more than once per year on average over a 3 year period. For 2008-

2010, the Nogales NA did not meet the NAAQS (i.e., as show in Table 2.2, the rate of expected 

exceedances is greater than 1.) 

Table 2.2

Nogales Filter-Based 24-hour PM10 Monitoring Data 1985-2010

Year

24-hour

Max

24-hour

2nd High

24-hour

3rd High

24-hour

4th High

Percentage 

of Valid 

Observations

Expected 

Exceedances

1985 110 88 85 83 31 0

1986 162 152 126 124 64 5.75

1987 232 166 160 135 77 18.33

1988 155 147 143 133 74 8.36

1989 244 168 145 138 69 15.33

1990 175 108 107 106 85 8.36

1991 164 149 112 110 95 6.1

1992 153 146 134 101 87 0

1993 119 108 86 72 74 0

1994 116 95 91 72 85 0

1995 123 107 80 77 87 0

1996 104 88 92 88 69 0

1997 126 93 84 77 84 0

1998 169 158 116 90 82 13.5

1999 184 184 152 119 83 15.5

 

18 The Nogales continuously operating Beta Attenuation Monitor (BAM) experienced significant technical 

difficulties in 2010 that resulted in the invalidation of half the year’s monitoring data. The BAM was originally sited 

as a Special Purpose Monitor in 2005 that is now used to determine compliance with the PM10 NAAQS. 
11

Table 2.2

Nogales Filter-Based 24-hour PM10 Monitoring Data 1985-2010

Year

24-hour

Max

24-hour

2nd High

24-hour

3rd High

24-hour

4th High

Percentage 

of Valid 

Observations

Expected 

Exceedances

2000 130 116 112 109 95 0

2001 213 112 96 95 93 6.9

2002 187 115 111 106 93 6.1

2003 184 162 125 119 100 12.3

2004 140 109 86 82 98 0

2005 279 205 156 144 97 17.93

2006 239 168 163 146 93 20

2007 190 133 122 115 97 6.1

2008 155 150 147 108 95 6.6

2009 123 116 109 105 95 0

2010 96 84 70 65 72 0

2008-2010 3-year Expected Annual Exceedances 2.2

Source: EPA’s Air Quality System database. 

Table 2.3

Nogales Continuously Operating BAM Monitor

 PM10 Monitoring Data 2005-2010

Year

24-hour

Max

24-hour

2nd High

24-hour

3rd High

24-hour

4th High

Percentage of 

Valid 

Observations

Expected 

Exceedances

2005 351 327 324 306 80 29

2006 271 256 240 233 89 42

2007 233 211 210 210 98 14

2008 234 217 206 204 97 13

2009 238 204 147 146 94 2

2010 191 177 175 163 17* 8.49

2008-2010 3-year Expected Annual Exceedances 7.83

Source: Ibid. *2010 monitoring data does not meet completeness criteria. 

 Figure 2.1 illustrates the complete ambient PM10 monitoring data history from 1985 through 

present for the filter monitor. This time period reflects ambient concentrations following the 

implementation of the control measures included in the 1993 Nogales NA SIP. As the data shows, the 

Nogales NA met the NAAQS by 1994 and showed values below the standard through 1998, after which 
12

exceedances of the standard were recorded. Since 1998, only 2000 and 2004 provided years with no 

observed exceedances of the NAAQS. 

 

Figure 2-1

Nogales Post Office Filter-Based PM10 Monitoring Data Trends 1985-2010

0

50

100

150

200

250

300

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

ug/m3

24hr Max 2nd 24hr High PM10 NAAQS

PM10 NAAQS

Source: EPA's AQS Database.

Figure 2-2

Nogales BAM Monitoring Data Trends 2005-2010

0

50

100

150

200

250

300

350

400

2005 2006 2007 2008 2009 2010

ug/m3

1st Hi 2nd Hi 3rd Hi 4th Hi PM10 NAAQS

Source: Ibid.

2.3 24-hour PM10 NAAQS Compliance 

 The primary (health) and secondary (welfare) 24-hour PM10 standards are met when the expected 

number of exceedances per year at each monitoring site is less than or equal to one. The expected number 

of exceedances per year is determined by recording the number of exceedances in each calendar year and 

averaging them over the past three years. Based on complete quality-assured data for 2008-2010, the 

number of expected exceedances of the 24-hour PM10 NAAQS for the Nogales NA is 2.2 for the filterbased monitor and 7.9 for the BAM monitor. Because the annual expected exceedance rate is greater than 

1.0, the Nogales NA is not currently meeting the PM10 standard. 
 

13

3.0 EMISSIONS INVENTORY 

 

 This chapter discusses the development of the emissions inventory required by the CAA Section 

172(c)(3). The 2008 emissions inventory for the Nogales NA 19 was developed starting with the 2008 

National Emissions Inventory (NEI) for Santa Cruz County. Then, county-level emissions estimates 

were apportioned to the Nogales NA based on population and land ratios, or actual location in the case of 

a stationary source. Figure 3.1 illustrates the major source categories in the Nogales NA in 2008. 

Figure 3.1

2008 Annual Emissions Inventory for the Nogales, Arizona 

PM10 Nonattainment Area

1,531 tons per year total

Other

87 tpy

6%

Residential 

Garbage Burning 

24 tpy

 2%

Residential 

Construction 

24 tpy Residential Wood 2%

Burning

24 tpy

 2%

Paved Road Dust 

121 tpy

 8%

Commercial/

Industrial 

Construction

 143 tpy

9% Road 

Construction

267 tpy

17%

Unpaved Road 

Dust 

865 tpy

 57%

Source: 2008 and 2011 PM10 Emissions Inventories for the Nogales NA, Santa Cruz County, 

Arizona (see Appendix B). Estimates are rounded. 

3.1 Significant Emissions Sources 

 The annual PM10 emissions inventory for the Nogales NA in 2008 is 1,531 tons per year 

(tpy). The four largest source categories comprise 90 percent of emissions generated in the Nogales 

NA. Those categories are fugitive dust from unpaved and paved roads, and dust generated by road 

and building construction. 

 The greatest source of emissions in the nonattainment area is fugitive dust from unpaved roads, 

accounting for 57 percent of annual emissions and 865 tpy. The 2008 emissions inventory determined 

that emissions from Road Construction are the second greatest source of PM10 emissions in the Nogales 

NA, accounting for 18 percent of annual emissions and 267 tpy. Fugitive emissions from Commercial 

 

19 The more detailed 2008 and 2011 PM10 Emissions Inventories for the Nogales Nonattainment Area, 

Santa Cruz County, Arizona are found in Appendix B of this plan. 
 

14

and Industrial sources are the third greatest source of PM10 emissions in the nonattainment area, 

accounting for nine percent of annual emissions and 143 tpy. Control measures for this source are 

discussed in Section 4.0. The fourth greatest source of PM10 emissions in the Nogales NA is dust from 

paved roads. Emissions for this category total eight percent of the 2008 emissions inventory and 121 tpy. 

 In total, the four emissions source categories discussed above account for 90 percent of 

annual emissions in the nonattainment area and 1,396 tons per year; see Table 3.1. The RACM 

implemented for these significant source categories and others are discussed in detail in Section 5.0. 

Table 3.1

Significant PM10 Emissions Sources in the Nogales NA, 2008

PM10 Source Categories TPY Percentage of 

Annual Emissions 

Fugitive Dust from Unpaved Roads 865 57 

Road Construction Dust 267 18 

Commercial and Industrial Construction Dust 143 9 

Paved Road Dust 121 8 

Total 1,396 90 

Source: 2008 PM10 Emissions Inventory for the Nogales NA (see Appendix B). Estimates are rounded. 

 Residential construction, and residential wood and waste burning, each account for 2 

percent of the 2008 annual emissions inventory. Those source categories are below the de 

minimis threshold, and therefore control measures are not required. Similarly, ADEQ determined 

that the emissions sources shown in Table 3.2 did not significantly contribute to ambient PM10

concentrations in the Nogales NA; therefore, control measures were not developed for these 

categories, which collectively account for three percent of the 2008 emissions inventory. The 

remaining minor source categories which contribute less than 2 tons of PM10 per year are 

included in Appendix B. 

Table 3.2 

PM10 Emissions Sources in the Nogales NA, 2008

PM10 Source Categories TPY 

Onroad Mobile - Diesel (includes exhaust, brake and tire wear) 19 

Onroad Mobile - Gasoline (includes exhaust, brake and tire wear) 8 

Commercial Cooking – Charbroiling 6 

Agriculture/Livestock Dust 4 

Prescribed Fires 3 

Non-road Gasoline Equipment 3 

Aircraft 2 

Total 45 

Source: Ibid. Estimates are rounded.
 

15

3.2 Nogales NA Future Year (2011) PM10 Emissions Projections 

 Projected emissions for 2011, shown in Table 3.3, were developed based on projected 

growth rates for population, industry, and motor vehicle activity for the Nogales NA. Motor 

vehicle emissions for 2011 are slightly lower than 2008 due to a newer cleaner fleet of vehicles 

and implementation of new fuel standards. The Federal Highway Administration's Highway 

Statistics statewide series data on Arizona shows a decline in Vehicle Miles Traveled (VMT) between 

2007 and 2008, and no change in VMT between 2008 and 2009. This trend is consistent with 

economic conditions. As discussed in Section 1.0, population and economic growth is not 

expected between 2008 and 2011 due to current economic conditions. Accordingly, no increases 

in source categories affected by these factors are projected. The complete projected inventory and 

methodology for emissions projections are included in Appendix B. 

Table 3.3 

Projected PM10 Emissions 2008 and 2011 (tons per year) 

Emissions Source Category 2008 

tpy 

2011 

tpy 

Projection 

Method 

Dust - Unpaved Road Dust 864.9 864.9 No growth 

Dust - Road Construction 267.0 267.0 No growth 

Dust - Commercial/Industrial/Institutional Construction 142.6 142.6 No growth 

Dust - Paved Road Dust 121.4 121.4 No growth 

Fuel Comb - Residential - Wood 24.0 25.7 Population 

Waste Disposal - Residential Garbage Burning 23.0 24.7 Population 

Dust - Residential Construction 23.9 23.9 No growth 

Mobile - Onroad Diesel (includes brake, tire, and exhaust) 19.4 13.2 Lower Emissions/MOVES 

Mobile - Non-Road Equipment - Diesel 8.5 8.5 No growth 

Mobile - Onroad Gasoline (includes brake, tire, and exhaust) 8.4 7.9 Lower Emissions/MOVES 

Commercial Cooking - Charbroiling 6.3 6.7 Population 

Fires - Prescribed Fires 3.4 3.4 No growth 

Agriculture - Crops & Livestock Dust 4.3 4.3 No growth 

Mobile - Non-Road Equipment - Gasoline 3.1 3.1 No growth 

Mobile - Aircraft 2.3 2.3 No growth 

Other (see Appendix B) 8.2 8.5 Various 

TOTALS 1530.7 1528.2 

Source: 2011 PM10 Emissions Inventory for the Nogales NA, Santa Cruz County, Arizona (see Appendix B). Estimates are rounded. 
 

16

4.0 Demonstration of Attainment in Accordance with Section 179B of the CAA 

 

 Section 179B of the Clean Air Act allows a State to demonstrate that exceedances of the PM10

NAAQS in the Nogales NA would not occur were it not for PM10 emissions from Nogales Municipality, 

Sonora, Mexico. In this section, the relevant data and observations taken from the following supporting 

analyses are reviewed: 

 Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona PM10

Nonattainment Area; 

 2008 and 2011 Emissions Inventories for the Nogales NA; 

 2008 and 2011 Emissions Inventories for the Nogales Municipality, Sonora, Mexico; and, 

 Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 

2007-2009. 

This section provides a summary of these supporting analyses for this determination of attainment of the 

PM10 NAAQS, but for international emissions. These four analyses are provided in full and can be found in 

Appendices A through D of this Nogales Plan.20 

Consistent with 40 CFR Part 50, appendix K, the standard used to determine attainment of the PM10

NAAQS in the Nogales NA, “but for” international emissions is as follows: the expected number of days 

per calendar year with a twenty-four hour average concentration above 150 μg/m3 must be equal to or less 

than one. Consequently, to determine that the Nogales NA has met the PM10 standard “but for” emissions 

from Mexico, the State must show through this analysis that no more than three exceedances (based on data 

completeness and every day sampling) over a three year period were due to emission sources arising within 

the Nogales NA, and that all other monitored exceedances of the NAAQS originate from Mexico. 

4.1 Population Growth in Nogales, Sonora 

 Population estimates provide an indication of anthropogenic PM10 emissions sources on both 

sides of the international border. The combined area of Nogales, Arizona, and the Nogales Municipality, 

Sonora, Mexico, is collectively known as Ambos Nogales. The Nogales Municipality, Sonora, Mexico 

 

20 The document “Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona PM10

Nonattainment Area” includes “2008 and 2011 Emissions Inventories for the Nogales NA”, “2008 and 2011 

Emissions Inventories for the Nogales Municipality, Sonora, Mexico”, and “Analysis of Ambient PM10 Levels, 

Topography, and Meteorological Data in Nogales, Arizona: 2007-2009” as supporting appendices A through C; 

therefore, all four analyses should be considered one document and when reading them one should keep in mind that 

they reference each other. 

For ease of reference within this Nogales plan, however, these four documents have been split apart, are provided 

each with their individual appendix, and are cited as such herein. To avoid confusion, please keep in mind this 

difference as a frame of reference. 
 

17

accounts for 90.2 percent of the 2010 population in the Ambos Nogales area.21 Figure 4.1, below, depicts 

the rapid/regular population growth of the Nogales Municipality, Sonora, and the consistently low or no 

population growth of Nogales, Arizona. 

Figure 4.1

Comparison of Ambos Nogales Population Growth 1995-2010

0

50

100

150

200

250

Thousands

Nogales Municipality, Sonora 133,491 159,787 193,517 220,292

Nogales, Arizona 20,184 20,878 20,421 20,837

1995 2000 2005 2010

4.2 Nogales, Sonora Emissions Inventories 

The 2008 and 2011 Nogales Municipality, Sonora emissions inventories shown in Table 4.1 were 

derived from Mexico's 1999 National Emissions Inventory, using a methodology explained in detail within 

Appendix C. The Nogales, Sonora emissions inventories contain low and high estimates for point sources and 

paved and unpaved roads due to the relative uncertainty of scaling or calculating these estimates. Point source 

estimates are presented as a range because different calculation methods produced a difference in results. Paved 

and unpaved road estimates are presented as a range given the range of sample data used to calculate these source 

categories. Again, the methods and data used to develop these emissions estimates can be found in Appendix C. 

In both high and low inventories, fugitive emissions from paved and unpaved roads were identified as the greatest 

sources of the ambient PM10 concentrations in Nogales, Sonora. See Table 4.1.

 

21 Table 1, "Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona PM10 Nonattainment Area” (see 

Appendix A). 
 

18

Table 4.1. 

2008 and 2011 PM10 Emissions Inventories for Nogales Municipality, Sonora (tpy)22

Source Category Range 2008 2011 

Point Sources Low Estimate 1.1 1.1 

 High Estimate 305 390 

Area Sources Unpaved Roads Low Estimate 2,144 2,308 

 High Estimate 5,521 5,944 

 Paved Roads Low Estimate 53 57 

 High Estimate 646 696 

 Agricultural Tilling 0.8 0.8 

 Agricultural Burning 1.6 1.6 

 Residential Wood Combustion 176 47 

 Open Burning of Waste 55 56 

 Construction Activities 23 24 

 Remaining Area Sources 159 150 

Mobile Sources 80 85 

Nonroad Sources 20 27 

Total Low Estimate 2,713 2,757 

Total High Estimate 6,987 7,420 

 

22 Emissions are rounded to the nearest ton/year, or to the nearest tenth of a ton/year for emissions less than ten tons/year. Source: 

"2008 and 2011 PM10 Emissions Inventories, Nogales Municipality, State of Sonora, Mexico", March 2012. (See Appendix C).
 

19

4.3 Comparison of Ambos Nogales Emissions Inventories 

Nogales NA, Arizona and Nogales Municipality, Sonora have similar sources of PM10, primarily 

fugitive dust from unpaved and paved roads, as well as combustion sources and construction. A comparison 

of the Nogales, Sonora 2008 low emission inventory and the 2008 Nogales NA inventory concludes that 

there is a 64/36 percent split in total Ambos Nogales emissions between emissions from Sonora and 

Arizona; a comparison of the 2008 high emission inventory suggests that there is an 82/18 percent split 

between emissions from Sonora and Arizona. Figure 4.2 depicts the emissions split. A different metric 

comparing the emissions inventory data shows that for every one ton of PM10 produced in the Nogales NA, 

there were between 1.8 and 4.6 tons of PM10 emissions produced annually in the Nogales Municipality. 

1531

6988

1531

2757

0

1000

2000

3000

4000

5000

6000

7000

PM10 

TPY

High Inventory Low Inventory

Figure 4.2

Nogales, Sonora 2008 High and Low Inventories 

Compared to Nogales NA 2008 Inventory

Nogales NA Emissions Nogales Municipality, Sonora Emissions

Source: Appendices B and C. 

4.4 PM10 Exceedance Analyses – Ambient Monitoring Data, Wind Speed, and Temperature Changes 

 For these analyses, ambient monitoring data from 2007-2009 collected by the by the continuously 

operating Beta Attenuation Monitor (BAM) monitor was examined; data collected by the BAM in 2010 

did not meet CAA completeness criteria, and 2011 data was not compiled and certified at the time of this 

analysis. Over the 2007-2009 timeframe, 29 exceedances of the NAAQS were recorded by the BAM at 

the Nogales, Arizona Post Office.23 Data recorded by the BAM monitor was selected for the analysis 

because the monitor recorded the greatest number of exceedances at the monitoring site and records 

hourly ambient PM10 values. The meteorological monitor at the site also provides hourly wind speed and 

direction data. The majority of the 29 exceedance days in our 2007 to 2009 study timeframe, 23 

exceedances (or 79 percent), occurred during October to January, mostly in November. See Figure 4.3. 

 

23 Arizona has not flagged any of these 2007 through 2009 exceedance days for potential exclusion from air quality planning 

considerations under EPA’s Exceptional Events Rule.
 

20

Figure 4.3 

PM10 Exceedances at the Nogales, Arizona Post Office, by Month and Year

Source: EPA AQS database. 

 Analysis of ambient air quality data identified 26 of the 29 exceedances as having nearly identical 

hourly emission, wind speed and temperature profiles. As shown in Figures 4.4 and 4.5, the exceedance 

days began with a repeated pattern of declining PM10 concentrations in the early morning hours followed 

by a pronounced increase starting at 6:00 am and a decline around 9:00 a.m. Figures 4.6 and 4.7 

demonstrate that wind speeds and temperatures rise, dispersing the spike in morning PM10 concentrations. 

As the day progresses, ambient PM10 concentrations reach their lowest points between 10:00 am and 4:00 

pm. As temperatures drop by as much as 20 degrees Fahrenheit over 3 to 4 hours and wind speeds drop 

through the evening, a spike in PM10 concentrations between 4:00 pm and 6:00 pm is observed that may 

correspond with evening commute hours. Ambient concentrations remain high for several hours through 

the evening, before eventually declining around 10:00 pm. 
 

21

Figure 4.4 

Hourly Ambient PM10 Concentrations on 29 Exceedance Days 

Source: "Analysis of Ambient PM10 Levels, Topography, and 

 Meteorological Data in Nogales, Arizona: 2007-2009" (see Appendix D)
 

22

Figure 4.5 

Hourly Ambient PM10 Concentrations on 26 Similar Exceedance Days, Excluding the 

Following Days: January 1, 2007; May 22, 2008; and January 1, 2009 

Source: Ibid.
 

23

Figure 4.6: 

Hourly Wind Speed Variations on 29 Exceedance Days 

Source: Ibid. 
 

24

Figure 4.7: 

Hourly Temperature Variations on 29 Exceedance Days 

Source: Ibid. 

4.5 Wind Direction and Pollution Rose Analyses 

 Wind roses were used to depict wind direction and speed on exceedance dates in Ambos Nogales. 

Wind roses depict hourly wind direction and wind speed values collected over 24 hours; the wind data is 

then sorted by direction so that the percentage of time that the wind was blowing from each direction can 

be determined. Wind speed data is then superimposed on each of the wind rose's twelve 30o segments to 

illustrate the average wind speed when the wind was blowing from that segment's direction. Figure 4.8 

depicts the wind speeds and directions for all of the 29 PM10 exceedances analyzed. A clear pattern of 

winds from a southerly direction traveling at low speeds emerges on exceedance days. 
 

25

Figure 4.8 

 Wind Rose of Wind Speed vs. Wind Direction at the Nogales, Arizona Post Office 

BAM Monitor for all 29 Exceedance Days 

 Source: Appendix D - Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007-2009

Pollution rose analyses substitute ambient hourly PM10 values for wind speed to provide a 

depiction of wind direction and correlated ambient concentrations. The result is a graphical representation 

of the possible directionality of pollution sources and the ambient concentration levels time-linked with 

those wind direction observations. See Figure 4.9. A review of the hourly ambient data shows that on 

exceedance days, 71-92 percent of hourly values exceeding 150 g/m3

 and 92 percent of the highest 
 

26

observed PM10 concentrations (above 450 g/m3), are associated with a southerly wind direction (135-225 

degrees).24 Appendix D includes additional wind and pollution rose analyses. 

Figure 4.9 

Pollution Rose of PM10 Concentration vs. Wind Direction at the Nogales, Arizona 

Post Office BAM for all 29 Exceedance Days 

Source: Appendix D - Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007-2009. 

 

24 See Table 11 in "Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona PM10 Nonattainment Area” 

(see Appendix A). Section 3.3.1 of that document provides additional analyses of ambient PM10 values and wind direction. 
 

27

4.6 A Conceptual Model of 2007-2009 Exceedance Days 

 As described in Section 4.4, 26 of the 29 2007 - 2009 exceedances showed a similar pattern of 

ambient PM10 concentration, wind speeds, wind direction, and temperature variation over a twenty-four hour 

period. The three exceptions were the January 1, 2007, May 22, 2008, and January 1, 2009 exceedance days. 

Two of these days, January 1, 2007 and January 1, 2009, with higher early morning PM10 concentrations, only 

vary slightly from the diurnal profile of PM10 concentrations observed for the other exceedances, but these two 

days have similar meteorological and concentration patterns throughout the rest of the day. Also, two of the 29 

exceedance days, January 1, 2007, and January 26, 2008, showed high average ambient concentrations during 

hours when the wind was from directions other than the southerly 90 degree quadrant (135-224 degrees on a 

compass). Thus, there are twenty-five exceedance days that are equivalent and can be considered here as a 

group, setting aside the dissimilar exceedance days listed above, January 1, 2007, January 26, 2008, May 22, 

2008, and January 1, 2009. These remaining 25 similar exceedance days provide the basis for a daily 

conceptual model consistent with ambient concentrations, wind speed and direction, temperature changes, 

diurnal heating and cooling pattern, and relative pollution loads discussed in sections 4.2, 4.3, and 4.4 above. 

See Figure 4.10. 
 

28

Figure 4.10 

Average Hourly PM10 Concentration, Wind Speed, and Temperature at the Nogales, Arizona Post Office 

BAM vs. Time of Day for all Exceedances Excluding January 1, 2007, May 22, 2008, and January 1, 2009 25

Source: Ibid. 

To review the conceptual model and average PM10 concentration, wind speed, and temperature 

profiles in Figure 4.10, beginning at midnight and through the early morning hours, there is a strong 

pattern of decreasing PM10 concentrations from the previous day’s high values. Then, in the morning 

hours, there is a pronounced PM10 increase and drop-off between 6:00 am and 9:00 am, suggesting an 

almost daily reproducible PM10 source, such as fugitive road dust from the morning commute. As 

morning temperatures rise, so does wind speed and wind direction changes from south to north dispersing 

the morning spike in PM10 concentrations. PM10 concentrations continue to fall through the afternoon and 

reach their lowest points between 10:00 am and 4:00 pm. The morning and afternoon increases in ambient 

temperature and wind speed can be attributed to the heating portion of a diurnal heating and cooling cycle 

where heated air flows from lower elevations to the north to the higher elevations to the south. 

 

25 The diurnal pattern shown in Figure 4.10 applies to 25 very similar exceedance days and also includes January 26, 2008 given 

this day’s similar diurnal profile. Elements of the conceptual model discussion, however, may not apply to January 26, 2008 

because of the higher observed PM10 concentrations when winds were from the east southeast and outside of the 90 degree 

southerly wind direction quadrant. For this reason, the January 26, 2008 exceedance day was examined in further detail along 

with the other three exceedance days, January 1, 2007, May 22, 2008, and January 1, 2009. 
 

29

As evening approaches and night falls, the diurnal cooling cycle begins as ambient temperatures drop 

and lower elevation air masses no longer rise with convection causing wind speed to drop and wind direction 

to vary. As temperatures continue into the night, wind speeds drop and cold air masses flow down from higher 

elevations in Nogales, Sonora causing wind direction to shift from a variable/northerly direction to a southerly 

direction. A corresponding and pronounced spike in PM10 concentration is observed beginning between 4:00 

pm and 6:00 pm, again suggesting an almost daily reproducible PM10 source, such as fugitive road dust from 

the evening commute. Concentrations remain high for several more hours into the night and gradually begin to 

decrease as midnight approaches. The highest concentrations of PM10 occur in these evening hours when dust 

from vehicle traffic on unpaved and paved roads may be captured by cold air flows from higher elevations and 

moving south to north. Also, home heating combustion may be part of the evening PM10 load and is captured 

in the evening northerly air flows. 

Usually, this pattern of exceedances is observed during times when the general weather pattern allows 

for stagnation and a relatively still air mass subject to movement by the diurnal cooling and heating cycle. At 

other times of the year, frontal weather systems move through often enough and with enough energy to prevent 

a stagnant air mass and the diurnal heating and cooling cycle from exerting a strong influence on the local 

meteorology and from causing exceedances of the PM10 standard. 

It should be noted that this conceptual model is consistent with the study by Arizona State University, 

“Atmospheric, Hydroclimatic, and Anthropogenic Causes of Fugitive Dust in the Nogales, Arizona-Nogales, 

Sonora Airshed.”26 In this study, the authors conclude that stagnant atmospheric conditions over a large scale 

are the most important factor in predicting high daily PM10 concentrations in the Ambos Nogales area. 

Finally, for these similar 25 days, the ambient concentration attributed to the southerly wind direction 

quadrant (90 degrees) always exceeds the 150 μg/m3

 level, in most cases markedly. Conversely, the ambient 

concentration attributed to the all other wind direction quadrants (the remaining 270 degrees) never exceeds 

the 150 μg/m3

 level. Across all 25 exceedance days, the average concentration value for the southerly wind 

direction quadrant concentration is 264 μg/m3

, with the range for each day’s average concentration being 163 

to 369 μg/m3

. In comparison, the average concentration value across these 25 exceedance days for the all other 

wind direction quadrants is 80 μg/m3

, with the range for each day’s average being 38 to 148 μg/m3.

27

4.7. Review of Exceedance Days Differing From 25-Day Conceptual Model 

 As described in Section 4.6, the data support the finding that at least 25 of 29 exceedances of the 

PM10 standard in the Nogales NA can be attributed to sources of PM10 originated from across the 

international border. There are, however, four exceedance days that differ in one or more ways from the 

conceptual model of PM10 exceedances in the Nogales NA: January 1, 2007; May 22, 2008; January 26, 

2008; and January 1, 2009. 

 

26 Completed in 2002 by A.W. Ellis, the final report is available through The Southwest Center for Environmental Research and 

Policy at http://scerpfiles.org/cont_mgt/doc_files/A-02-2.pdf. 27 See Table 12 of Appendix A for average hourly concentrations segregated into those attributed to the southerly wind quadrant 

and the 270 degree all other wind direction quadrant for all exceedance days. 
 

30

January 1, 2007 and January 1, 2009 had a diurnal pattern that varied from the conceptual model 

and further analysis showed a higher PM2.5 component compared to the remaining 27 exceedance days, 

suggesting a larger contribution from combustion sources such as residential wood burning.28 See Figures 

4.11 and Figure 4.12. 

Figure 4.11 

January 1, 2007 PM10 Concentrations and Wind Speeds Compared to 26 Exceedance 

Day Average PM10 Concentrations and Wind Speeds from Figure 4.10 

Source: Appendix D - Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007-2009. 

 

28 See Section 4.4, of Appendix D for discussion of PM2.5 concentrations relative to PM10 concentrations for the 29 exceedance 

days. 
 

31

Figure 4.12 

January 1, 2009 PM10 Concentrations and Wind Speeds Compared to 26 Exceedance Day 

Average PM10 Concentrations and Wind Speeds from Figure 4.10 

Source: Ibid. 

The May 22, 2008 exceedance is associated with high winds. Most of the highest hourly 

concentrations in the 29 exceedance days occurred on May 22, 2008. The PM coarse component on this 

day was higher compared to the remaining 28 exceedance days suggesting a large contribution from 

fugitive dust sources such as open area, and unpaved and paved roads.29 Furthermore, all wind direction 

observations were southerly. See Figure 4.13 below. 

 

29 See Section 4.4 of Appendix D for discussion of PM2.5 concentrations relative to PM10 concentrations for the 29 exceedance 

days. 
 

32

Figure 4.13 

May 22, 2008 PM10 Concentrations and Wind Speeds Compared to 26 Exceedance Day 

Average PM10 Concentrations and Wind Speeds from Figure 4.10 

Source: Appendix D - Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007-2009. 

 

 As described earlier, January 26, 2008 has a similar diurnal pattern to the 25-day conceptual 

model. See Figure 4.14. Other elements of the conceptual model, however, may not apply to January 26, 

2008 because of the higher observed PM10 concentrations when winds were from the east-southeast and 

outside of the 90-degree southerly wind direction quadrant. This results in high average concentrations 

for all the other wind direction quadrants. See Table 4.2 below. 

Figure 4.14 

January 26, 2008 PM10 Concentrations and Wind Speed Compared 

Average PM10 Concentrations and Wind Speeds from Figure 4.10 

 Source: Ibid. 
 

33

In addition to diurnal patterns, high concentrations from the “all other wind direction” quadrants were 

examined for these four exceedance days. On all 29 exceedance days, the ambient PM10 concentration attributed 

to the southerly wind quadrants exceeds 150 μg/m3

. In contrast, two exceedance days from the “all other wind 

direction” quadrants show a value greater than 150 μg/m3: January 1, 2007 and January 26, 2008. Only one of 

29 exceedance days shows the concentration attributed to the “all other wind direction” quadrant greater than that 

of the concentration attributed to the southerly wind quadrant: January 1, 2007. See Table 4.2. 

Table 4.2

24-hour Concentration and Hourly Concentrations Disaggregated by Southerly Wind Direction 

Quadrant for Exceedance Days Differing from Conceptual Model

Date 24-hour PM10

Concentration 

(μg/m3) 

Southerly Wind Quadrant 

PM10 Average Concentration 

(μg/m3) (135 to 224 degrees) 

All Other Wind Direction 

PM10 Average Concentration 

(μg/m3) (225 to 134 degrees) 

January 1, 2007 210 199 (15 of 24 values) 231 (9 of 24 values) 

January 26, 2008 204 257 (7 of 24 values) 182 (17 of 24 values) 

May 22, 2008 217 217 (24 of 24 values) No Observed Values 

January 1, 2009 238 323 (14 of 24 values) 119 (10 of 24 values) 

Source: Air Quality System database. 

4.8 Expected Exceedance Days “But For” International Transport from Mexico

Consistent with 40 CFR Part 50, appendix K, the standard used to determine attainment of the 

PM10 NAAQS in the Nogales NA, “but for” international emissions is as follows: the expected number of 

days per calendar year with a twenty-four hour average concentration above 150 μg/m3

 must be equal to 

or less than one. Consequently, to determine that the Nogales NA has met the PM10 standard “but for” 

emissions from Mexico, this analysis must show that no more than three exceedances (based on data 

completeness and every day sampling) in the 2007-2009 analysis period were due to emission sources 

arising within the Nogales NA, and that all other monitored exceedances of the NAAQS originate from 

Mexico. Two analyses were used to examine the issue of expected exceedances but for international 

emissions: a daily analysis reviewing selected exceedance days; and, an analysis of observed hourly 

concentrations designed to estimate a Nogales NA 24-hour average concentration after accounting for the 

influence of international emissions. 

4.8.1 Daily Analysis of Expected Exceedances 

From the day-by-day review above, it is possible to determine whether or not to assign the four 

exceedance days in question, January 1, 2007, January 26, 2008, May 22, 2008, and January 1, 2009 to 

the category of exceedance days having a significant contribution from sources on the Nogales, Sonora 

side of the international border. 

The May 22, 2008 exceedance day is completely different from the conceptual model exceedance 

day because of the relative high wind speeds and higher than usual coarse PM (e.g., unpaved roads) 

component. As with total PM10 emissions, emissions of coarse PM are higher from Nogales, Sonora, than 
 

34

they are from the Nogales NA. The wind direction is from a southerly quadrant in all hourly 

concentration observations. Given this information, this day should be placed with the 25 other 

exceedance days in the conceptual model, because it is likely that the sources of PM10 causing the 

exceedance originated from the Nogales, Sonora side of the international border. 

The January 1, 2009 exceedance day is different from the conceptual model exceedance day in 

the timing and distribution of observed ambient PM10 values and high PM2.5 component most likely 

caused by a combustion source. As with total PM10 emissions, emissions of fine PM (e.g., combustion 

sources) are higher from Nogales, Sonora, than they are from the Nogales NA. The key factor for 

assigning this day is the contribution of high hourly ambient concentrations with a southerly wind 

direction quadrant compared to the remaining 270 degree wind direction quadrants (see Table 4.2 above). 

Consequently, this day should be placed with the 25 other exceedance days in the conceptual model, 

because it is likely that the sources of PM10 causing the exceedance originated from the Nogales, Sonora 

side of the international border. 

Considering the January 1, 2007 exceedance day, it also differs from the conceptual model 

exceedance day in the timing and distribution of observed ambient PM10 values and high PM2.5

component. What differs in the case of the January 1, 2007 exceedance is that the 270 degree wind 

direction quadrants contains enough high values to contribute disproportionately to the overall twentyfour hour average concentration (see Table 4.2). Although more detailed and different field studies might 

prove otherwise, with the information available, this analysis is inconclusive as to whether this 

exceedance can be attributed solely to a disproportionate international contribution from Nogales, Sonora. 

Finally, the January 26, 2008 exceedance day is most like the conceptual model exceedance day 

in the timing and distribution of observed ambient PM10 values. While the southerly wind direction 

quadrant contains enough high values to contribute disproportionately to the overall twenty-four hour 

average concentration, there are enough remaining high values in the 17 of 24 hourly observations from 

the 270 degree wind direction quadrants to be above the 150 μg/m3

 level (see Table 4.2). Again, while 

specifically designed field studies might help determine the relative contributions to this exceedance, with 

the information available, this analysis is inconclusive as to whether this exceedance can be attributed 

solely to a disproportionate international contribution from Nogales, Sonora. 

To summarize, two exceedance days, May 22, 2008 and January 1, 2009, should be categorized 

with the 25 exceedance days where there is a high likelihood of a large contribution of PM10 from sources 

on the Nogales, Sonora side of the international border across from the Nogales NA. The two remaining 

exceedance days, January 1, 2007 and January 26, 2008, may have a contribution from sources on the 

Nogales NA side of the international border such that one cannot say whether there is a high likelihood 

that the area would not have exceeded the PM10 standard but for PM10 emissions originating from the 

Nogales, Sonora side of the international border. 
 

35

4.8.2 Hourly Analysis of Expected Exceedances 

In this analysis, each hourly concentration value from the 29 exceedance days was classified based on 

the likely influence from Mexico according to four criteria or decision rules. An hourly concentration value that 

was classified by a given decision rule was then weighted by 0.36, representing the maximum proportion of 

Nogales NA emissions compared to the total Ambos Nogales regional emissions and equivalent to assuming a 36 

percent contribution from U.S. sources during those hours.30 Then, a 24-hour average concentration was 

recalculated to determine what concentration would have occurred but for international transport of PM10

emissions from Nogales, Sonora. 

 To review the decision rules for classifying the hourly values per Mexican influence, the first 

decision rule identified periods consistent with sustained high winds from the south carrying wind-blown 

dust, as discussed earlier concerning the May 22, 2008 exceedance day. The second and third decision 

rules identified daily periods influenced by downslope wind flow conditions usually occurring in the late 

afternoon and evening, indicative of sustained downslope air flows from higher elevations south of the 

international border. The fourth decision rule identified periods of sustained air mass stagnation usually 

found in the late night and early morning hours after the early evening downslope wind or air flow has 

ebbed and before sunrise, after which wind speeds begin to increase from their overnight low values. 

 

 To show the effects of each decision rule, an estimated 24-hour concentration was calculated after 

the application of Rule 1, Rules 2 and 3, Rules 1-3, and Rules 1-4. The results are summarized below.31

 

 The application of Rule 1 only removes one day, May 22, 2008; leaving 28 days showing a 

concentration value greater than 150 μg/m3

. 

 The application of Rules 2 and 3 removes 27 days; leaving January 1, 2007 and January 26, 2008 

showing a concentration value greater than 150 μg/m3

 ; 196.8 μg/m3 and 244.1 μg/m3, respectively. 

 The application of Rules 1, 2, and 3 again removes 27 days; leaving January 1, 2007 and January 

26, 2008 showing a concentration value greater than 150 μg/m3

; 196.1 μg/m3 and 244.1 μg/m3, 

respectively. 

 The application of Rules 1, 2, 3, and 4 removes 29 days; leaving no estimated days with a value 

greater than 150 μg/m3

. 

 In conclusion, this analysis of hourly concentration values, demonstrates that at least 27 of 29, 

and possibly all 29 exceedances of the PM10 NAAQS observed in the Nogales NA during 2007 - 2009 can 

be attributed to sources of PM10 from across the international border. 

 

30 See the emission inventory comparisons of the Nogales NA and the Nogales Municipality in Section 4.3. 31 See Section 3.7 of Appendix D “Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, 

Arizona: 2007-2009” for a complete discussion of the decision rules and all estimated 24-hour concentrations. 
 

36

4.9 Conclusion 

 A nonattainment area meets the national ambient air quality standard (NAAQS) for PM10 when 

the expected number of days per calendar year with a twenty-four hour average concentration above 150 

μg/m3

 are less than or equal to one. To determine that the Nogales NA has met the PM10 standard “but 

for” emissions from Mexico, this analysis must show that no more than three exceedances of the standard 

in the 2007-2009 analysis period were due to sources within the Nogales NA and all other exceedances 

were caused by sources originating from across the international border. This analysis found that 27 of 29 

exceedance days were due to transport of PM10 emissions from sources on the Nogales, Sonora side of the 

international border. Consequently, when considering a maximum of two remaining exceedances, the 

expected annual exceedance rate for 2007-2009 is 0.7 exceedances per year. Since the annual expected 

exceedance rate is less than one, the State has demonstrated that the Nogales NA would attain the PM10

NAAQS “but for” PM10 emissions originating in Mexico. 
 

37

5.0 CONTROL MEASURES 

 This section discusses the selection, implementation, and results of reasonably available control 

measures (RACM) and technology (RACT) implemented in the Nogales Nonattainment Area (NA). 

 The Arizona Administrative Code (AAC) rules already approved in the State SIP and relied upon 

for this plan are listed in Table 5.1. 

5.1 Definition and Selection of RACM/RACT 

 EPA defines RACM/RACT as measures that a State finds are both reasonably available and 

contribute to attainment as expeditiously as practicable. When developing a SIP for a moderate PM10 

nonattainment area, the State is required to provide an analysis identifying which of EPA’s RACM and 

RACT are appropriate for controlling significant PM10 sources. The State is instructed to begin with EPA’s 

suggested RACM and RACT for fugitive dust, prescribed burning, and residential wood burning (57 FR 

13540; April 16, 1992). The CAA also directs the State to consider potential control measures proposed by 

the local community during the public comment period as well as RACM in other similar areas. The RACM 

selected by the State must provide emissions controls for sources identified in the emissions inventory as 

significant sources of PM10 emissions. RACM are not required for insignificant sources, controlled sources 

where additional measures would not expedite attainment of the NAAQS, or for sources not present in the 

nonattainment area. 

 The emissions inventory in the 1993 Nogales NA SIP and the 2008 emissions inventory in Section 

3.0 cited the same significant PM10 emissions source categories for the Nogales NA. Accordingly, ADEQ is 

evaluating the implementation of control measures from the 1993 Nogales NA SIP within this plan. 

 

32 R18-2-702, General Provisions, reflects the current R18 Arizona Administrative Code numbering format. The R9 series of 

rules were subsequently renumbered as well, but have only been approved by EPA in the original numbering format.

Table 5-1 

Arizona Administrative Code Rules Approved into the Arizona SIP for PM10 Sources

Rule FR Date FR Citation 

R9-3-404 Open Areas, Dry Washes, or Riverbeds 4/23/1982 47 FR 17485 

R9-3-405 Roadways and Streets 4/23/1982 47 FR 17485 

R9-3-406 Material Handling 4/23/1982 47 FR 17485 

R9-3-407 Storage Piles 4/23/1982 47 FR 17485 

R9-3-410 Evaluation of Non-point Source Emissions 4/23/1982 47 FR 17485 

R9-3-502 Standards of Performance for Unclassified Sources 10/19/1984 49 FR 41026 

R9-3-522 Standards of Performance for Existing Gravel and 

 Stone Crushing Operations 

9/28/1982 47 FR 42572 

 R18-2-70232 General Provisions 8/24/2004 69 FR 51952 
 

38

5.1.2 RACM Analysis for the Nogales NA Area 

 The emissions inventory in ADEQ’s 1993 Nogales NA SIP identified emissions from unpaved 

roads as the greatest source of PM10 emissions generated in the Nogales NA.33 ADEQ accordingly 

consulted EPA guidance (57 FR 13540; April 16, 1992) to identify control measures for inclusion in the 

1993 Nogales Nonattainment Area (NA) SIP. This subsection examines the selection process, 

implementation, current status and applicability of control measures required in ADEQ’s 1993 SIP for the 

Nogales NA. 

 Because no new significant source categories were identified in the 2008 emissions inventory, 

ADEQ determined that the control measures from the 1993 Nogales NA SIP are still appropriate controls 

for the area. The following sections discuss why the RACM/RACT were initially selected and provides 

an explanation of their implementation status. The control measures selected in the 1993 Nogales NA 

SIP continue to be required in this SIP revision. Some of the 1993 control measures are not submitted for 

incorporation within the SIP and SIP credit because they are not enforceable by the State or have not been 

submitted to the Arizona SIP; those measures are clearly labeled as such. 

5.2 Control Measures Adopted into the SIP and Implemented by ADEQ 

The control measures implemented by ADEQ include the following: 

 

1. Require RACT for stack and fugitive PM10 from permitted stationary sources; 

2. Require RACT for haul roads and staging areas; 

3. Require dust control measures for material storage piles; 

4. Limit Use of Recreation Vehicles on Open Land. 

Most of these control measures are listed in Table 5-1 and are discussed further below. 

5.2.1 Require RACT for Stack and Fugitive PM10 from Permitted Stationary Sources/ 

 Require RACT for Haul Roads and Staging Areas 

 In the 1993 Nogales NA SIP, ADEQ committed to implement the RACM/RACT for stack and 

fugitive emissions from permitted stationary sources, haul roads and staging areas, and material storage 

piles. The sources permitted by ADEQ shown in Table 5.2 were in operation during 2008. With the 

exception of the UNS Electric facility, which operates under a Title V permit, the sources below operate 

under one of ADEQ’s general permits that require RACM/RACT appropriate for the source. In addition, 

R18-2-702, effective February 3, 2004 (69 FR 51592; August 28, 2004) establishes a 20 percent opacity 

standard for point sources in all moderate PM10 nonattainment and maintenance areas, including the 

Nogales NA, and qualifies as RACM. EPA states, "Where the sources affected by a particular measure 

 

33 See Table 3.1 on page 27 of the 1993 NA SIP. “Final State Implementation Plan for the Nogales PM10 Nonattainment 

Area.” ADEQ. Submitted to EPA June 14, 1993. <http://www.azdeq.gov/environ/air/plan/download/nogpm10sip_061993.pdf>
 

39

contribute only negligibly to ambient concentrations that exceed the NAAQS, EPA's policy is that it 

would be unreasonable and therefore would not constitute RACM to require controls on the source."34

Emissions from permitted sources meet these criteria and, therefore, do not require RACM. 

 

Table 5.2

 PM10 Generating Point Sources Operating in the Nogales NA in 2008

Company Name Place Description PM10 

TPY

Type

County Health Department Boilers and Generators 0.019 Stationary

AT&T Generator 0.002 Stationary

Steris Inc. Medical Device Sterilization N/A35 Stationary

UNS Electric Inc. Utilities – Natural Gas 0.610 Stationary

Wash and Clean World Dry Cleaners 0.011 Stationary

CEMEX Construction Materials South Concrete Batch Plant 1.662 Portable

Total 2.3 tpy 

Source: ADEQ. 

5.2.2 Require Dust Control Measures for Material Storage Piles 

AAC R9-3-407, approved into the Arizona SIP by EPA April 23, 1982 (47 FR 17485), prescribes the 

following requirements for storage piles: 

 

 A. No person shall cause, suffer, allow, or permit organic or inorganic dust producing material to be 

stacked, piled, or otherwise stored without taking reasonable precautions such as chemical stabilization, wetting, 

or covering to prevent excessive amounts of particulate matter from becoming airborne. 

 B. Stacking and reclaiming machinery utilized at storage piles shall be operated at all times with a 

minimum fall of material and in such manner, or with the use of spray bars and wetting agents, as to prevent 

excessive amounts of particulate matter from becoming airborne.

 ADEQ officials are authorized to issue citations for violating the law. 

5.2.3 Limit Use of Recreation Vehicles on Open Land 

 The City of Nogales is well-developed and city officials confirm there are no open public areas 

where off-highway vehicles (OHVs) can be used within its borders. The prohibition on OHV use is 

enforced by local law enforcement agencies. Portions of the Nogales NA with open areas are subject to 

 

34 EPA. PM10 Moderate Area SIP Guidance: Final Staff Work Product. April 2, 1991. 

<http://gate1.baaqmd.gov/pdf/1321_PM10_Moderate_Area_SIP_Guidance_Final_Staff_Work_Product_1991.pdf> 35 Exact emissions for Steris Inc are not available as their emissions are below reporting requirements. If a source emits below one ton per 

year of any single pollutant or below two and one-half tons of combined pollutants, the source is not required to report their emissions to 

ADEQ.
 

40

Arizona Administrative Code (AAC) R9-3-404 - Open Areas, Dry Washes, or Riverbeds, approved into 

the Arizona SIP on October 19, 1984 (49 FR 41026), which establishes that “No person shall operate a 

motor vehicle for recreational purposes in a dry wash, riverbed or open area in such a way as to cause or 

contribute to visible dust emissions which then cross property lines into a residential, recreational, 

institutional, educational, retail sales, hotel or business premises. For purposes of this subsection "motor 

vehicles" shall include, but not be limited to trucks, cars, cycles, bikes, buggies and 3-wheelers. Any 

person who violates the provisions of this subsection shall be subject to prosecution under A.R.S. § 49-

463.”36 Enforcement of the law is provided by Arizona Department of Public Safety officers, sheriffs, 

police, and State and federal land managers. Violations of the law may lead to penalties reaching $500.00. 

5.3. Status of 1993 Nogales NA SIP Control Measures Implemented by the City of Nogales 

 and/or Santa Cruz County Meeting RACM 

 This section provides a status report on the control measures included in the 1993 Nogales NA 

SIP implemented by the City of Nogales and Santa Cruz County. These measures are included in this SIP 

revision and continue to be enforceable and implemented.

5.3.1 Pave or Chemically Stabilize Unpaved Roads; Pave, Vegetate or Chemically 

 Stabilize Access Points Where Unpaved Traffic Surfaces Adjoin Paved Roads 

 All public roads in the City of Nogales have been paved and accepted into the City’s Street 

Maintenance Program; therefore, there are no unpaved/paved road access points between adjoining public 

roads.37 Santa Cruz County officials confirm the portions of Rio Rico within the nonattainment area 

boundaries include approximately 200 miles of paved/double chip-sealed roads, with approximately 40 

miles of unpaved roads at present.38 Because the map provided by the County does not differentiate 

between paved and unpaved roads, ADEQ created its own map of unpaved roads in the Nogales NA; the 

map is included in Appendix E.3. ADEQ's estimate for double chip-sealed roads in the Rio Rico portions 

of the nonattainment area is 134.4 miles; the estimate for unpaved roads is 53.5 miles. 

 Between 1992 and 2008, 17.5 combined miles of roadway were paved or double chip-sealed in 

the Rio Rico and Nogales portions of the Nogales NA. In Appendix E, the State presents two methods of 

calculating emission reductions for these chip sealed roadways. Method One assumes double chip-sealing 

provides 90 percent control efficiency of emissions; Method Two assumes double chip-sealing provides 

emissions rates equivalent to paving the roadways. 

 

 

36 Arizona Administrative Code. R18-2-604, formerly R9-3-404, approved by EPA in 1984 (49 FR 17485). 

<http://www.azsos.gov/public_services/Title_18/18-02.htm> 37 Correspondence. Juan Guerra, Nogales City Engineer. See Appendix F.3.

38 Correspondence. Jesus Valdez, P.E. Interim Public Works Director County Engineer, Santa Cruz County. See Appendix F.2.
 

41

 Within the 1993 Nogales NA SIP, the City of Nogales committed to pave several roadways within the 

city limits by 1998.39 In an implementation review using aerial photography, ADEQ identified eleven unpaved 

roads that were paved between 1992 and 1996 totaling 8.4 miles. Because traffic data could not be located for 

two of the eleven roadways (Hohokam and La Quinta Roads) emission reductions were not calculated for 

them. For the remaining 9 unpaved roads totaling 7.7 miles, the annual emission reduction associated with 

their paving is estimated to be 78.45 tons per year, as shown in Table 5.3.40 See Appendix E for calculations. 

 In a similar implementation review using aerial photography41 and data provided by Santa Cruz 

County,42 ADEQ also reviewed 39.8 miles of road paving/double chip-sealing completed by the County in the 

Rio Rico community in and around the Nogales NA between 2002-2008. Of those, ADEQ identified four 

unpaved roads within the Nogales NA totaling 9.75 miles, as shown in Table 5.4.43 The annual emission 

reductions associated with the paving of these four unpaved roads is estimated to be 107.4 tons per year. See 

Appendix E for calculations. While there was an additional estimated 40 miles of paving/double chip-sealing 

projects on unpaved roads in the Rio Rico community between 1994-2001, Santa Cruz County could not 

locate records detailed enough to allow ADEQ to calculate emission reductions for the subset of these projects 

located in the nonattainment area.44 As a result, ADEQ did not claim emissions reductions for these projects. 

As shown in Tables 5.3 and 5.4, within the Nogales NA, the City of Nogales and Santa Cruz County 

have paved 17.45 miles of unpaved roads resulting in 185.5 tpy of emissions reductions based on Method 2. 

Table 5.3 

Calculated PM10 Emissions for Roads in the City of Nogales, Arizona 1993-1996 

Roadway Miles 

Paved 

VMT 

Unpaved 

Emissions 

(tons) 

Paved 

Emissions 

(tons) 

Royal Rd 0.9 16178 4.55 0.0086 

Vista del Cielo 2.2 160072 45.06 0.0848 

Yucca Drive S. 2.0 13696 3.86 0.0073 

Bristol Dr 0.4 7875 2.22 0.0042 

Frank Reed Rd 0.95 62616 17.63 0.0332 

Kino Rd 0.28 3835 1.08 0.0020 

Kelsey Rd 0.27 6240 1.76 0.0033 

West 1st St 0.4 6848 1.93 0.0036 

Target Range Rd 0.2 1294 0.36 0.0007 

Total 7.7 278655 78.45 0.148 

 

39 Pages 31-32 of “Final State Implementation Plan for the Nogales PM10 Nonattainment Area.” ADEQ. Submitted to EPA June 

14, 1993. <http://www.azdeq.gov/environ/air/plan/download/nogpm10sip_061993.pdf> 40 See Appendix E, Table E.5. 

41 Correspondence. Letter from EPA to ADEQ dated November 30, 1993. See Appendix E.4. 

42 Correspondence. Jesus Valdez, Interim Public Works Director, Santa Cruz County Engineer. See Appendix F.2.

43 See Appendix E, Table E.1. 

44 Correspondence. Jesus Valdez, Interim Public Works Director, Santa Cruz County Engineer. See Appendix F.5. 
 

42

Table 5.4 

Calculated PM10 Emissions for Roads in 

Rio Rico within the Nogales NA, 2002-2008 

Roadway 

Miles 

Paved VMT 

Unpaved 

Emissions 

(tons) 

Paved 

Emissions 

(tons) 

Calle Arikara 1.09 22694 5.9 0.011 

Paseo Mexico 4.03 195774 35.5 0.067 

Calle CoyoteAnnette Ct 

1.92 65679 18.5 0.035 

Paseo Guebabi 2.70 168746 47.5 0.089 

Total 9.75 452893 107.4 0.202 

ADEQ used the latest satellite images available to assess paved and unpaved road intersections in 

Rio Rico in 2011 and found that, typically, intersections provided adequate stabilization of unpaved roads 

to mitigate trackout. As shown in Figure 5.1, soil trackout from the typical unpaved road in Rio Rico 

visibly trails off as vehicles approach the main paved road due to the paved apron transition area, 

decreasing trackout and reentrained emissions. Figure 5.1 is only provided as a demonstration of a typical 

apron in Rio Rico located with Google Maps; the intersection of Calle Remedios and Calle Carmelita is 

an example of the County's efforts to mitigate trackout onto paved roads. 

Figure 5.1 

Typical Intersection of Paved and Unpaved Road in Rio Rico 

Source: Google Maps.
 

43

As part of preventing track out on to paved roads, Section 8-8-2, Streets, of the City of Nogales 

Code requires curbing of paved roads and Section 8-9-5, General Parking Lot Design Requirements, 

requires paving of commercial parking lots; these measures are included as supplementary information in 

Appendix G and are not included for submittal with this SIP or for consideration as RACM.

5.4 Control Measure Implemented by Agencies but not included in the SIP for Credit 

 The control measures in this section provide additional emissions reductions in the Nogales NA 

but are not claimed for credit. 

5.4.1 General Services Administration (GSA) Reduce Idling Time of Diesel-Powered 

 Vehicular Traffic at Border Entrances 

 As reported by ADEQ in its 1996 Reasonable Further Progress report,45 by 1994 the GSA 

expanded the number of northbound vehicle lanes at the DeConcini Port of Entry (POE) from four to 

eight, and added three northbound lanes at the Mariposa POE. These actions provided supplemental 

reductions in exhaust and brake wear emissions, vehicle stops and starts, and idling time. 

5.4.2 Provide for Storm Water Drainage to Prevent Soil Erosion onto Paved Roads/ 

 Provide for Traffic Rerouting or Rapid Clean Up of Temporary Sources of Dust on 

 Paved Roads 

 Two problem storm drainage areas in the City of Nogales identified in the 1993 Nogales NA SIP 

(Meadow Hills, Yucca Drive) were repaired with box culverts and paved with concrete. The City owns two 

standard street sweepers; maintenance is performed on a 5-day, 40-hour weekly basis.46 Santa Cruz County 

implemented an on-call program for Public Works Department employees to be on standby after normal 

working hours to respond to road emergencies and/or road blockage following a storm. Public Works crews 

immediately perform clean up after every storm event by removing debris and sweeping the road.47 The 

County currently has two standard street sweepers. The County cleans roads on a routine, 5-day, 40-hour 

workweek basis. Section 8-6-6 of the City of Nogales Code, Surface Drainage and Storm Sewer System, 

and 8-16-23, Design Standards for On-site Retention of Storm Water, provide measures to prevent storm 

water and soil from flooding city streets. The County and City have local laws to prevent water erosion onto 

paved roads; these measures are included as supplementary information in Appendix G and are not included 

for submittal with this SIP.

 

45 ADEQ. Nogales PM10 Nonattainment Area Quantitative Milestone/Reasonable Further Progress Report. June 12, 1996. See Appendix I.

46 Correspondence. Juan Guerra, Nogales City Engineer. See Appendix F.3.

47 Correspondence. Jesus Valdez, P.E. Interim Public Works Director, Santa Cruz County Engineer. See Appendix F.2. 
 

44

5.4.3 Prohibit Permanent Unpaved Haul Roads, and Parking or Staging Areas at Commercial, 

 Municipal, or Industrial Facilities 

Section 8-9-5 of the Nogales City Building Code, General Parking Lot Design Requirements, and 

Article 11 of the Santa Cruz County Zoning Code provide regulations for this category and are included 

as supplementary information in Appendix G. RACM for haul roads required by the operating permits 

issued by ADEQ for sources in the Nogales NA is discussed in subsection 5.2.1. 

5.4.4 Require Haul Trucks to be Covered 

 Arizona Revised Statute 28-1098, effective September 19, 2007, requires that “For the purpose 

of highway safety or air pollution prevention, a person shall not drive or move a vehicle on a highway 

unless the vehicle is constructed or loaded in a manner to prevent any of its load from dropping, sifting, 

leaking or otherwise escaping from the vehicle...A person shall not operate a vehicle on a highway with a 

load unless the load and any covering on the load are securely fastened in a manner to prevent the 

covering or load from becoming loose, detached or in any manner a hazard to other users of the 

highway.” Department of Public Safety deputies and local law enforcement officials are authorized to 

issue citations for violating the law. [Emission reductions resulting from enforcement of ARS 28-1098 

are supplemental for this plan.] 

5.5 Nogales NA RACM/RACT Conclusion 

 The implementation of these measures ensured the Nogales NA attained the PM10 standard by the 

December 31, 1994 deadline established by the 1990 amendments of the CAA (76 FR 1532; January 11, 

2011). Monitoring data following the implementation of these measures demonstrates emissions 

reductions were sufficient to attain the NAAQS through 1998. As discussed in Section 4.0, subsequent 

violations of the PM10 NAAQS can be attributed to emissions originating in Mexico. The RACM 

identified by ADEQ’s 1993 Nogales NA PM10 SIP are still appropriate controls based on the 2008 base 

year emissions inventory included in Section 3.0. 

The greatest emissions sources, fugitive emissions from unpaved roads, have been effectively 

controlled in the Nogales NA as discussed earlier in this chapter. All public roads within the City of 

Nogales have been paved. Approximately 80 miles of roads in Rio Rico have been double chip-sealed, 

although emission reduction credit is taken for only 9.75 miles within the Nogales NA that could be 

verified with documentation. Implementation analysis of road paving projects completed within the 

Nogales NA by the City of Nogales and Santa Cruz County over the period 1992-2008 show that a 

combined total of 17.45 miles of unpaved roads have been paved/double chip-sealed, resulting in a 

reduction of 185.5 tons per year in PM10 emissions. 

 To control fugitive emissions from paved roads, both the City of Nogales and Santa Cruz County 

own two standard street sweepers. The City and County clean roads on a routine, 5-day, 40-hour work 
 

45

week basis. Appendix G includes supplementary information on local ordinances and codes that help 

control emissions from this category. 

 In conclusion, paving project RACM/RACT implemented in the Nogales NA by the City of 

Nogales and Santa Cruz County are permanent and continue to produce emission reductions. State control 

measures supporting the plan have been incorporated within the SIP (see Table 5.1). Control measures 

implemented by the GSA, by Santa Cruz County, and by the City of Nogales provide additional 

emissions reductions toward attainment but are not credited in this plan. 
46

6.0 REASONABLE FURTHER PROGRESS AND CONTINGENCY MEASURES 

 

The federal Clean Air Act (CAA), Section 189(c), requires PM10 nonattainment areas to include 

reasonable further progress (RFP) milestones, which are to be achieved every three years until the area is 

redesignated attainment or meets the NAAQS. 

On January 11, 2011, EPA promulgated a determination of attainment as of the applicable attainment 

date for the Nogales NA based on ambient air quality monitoring data from 1992-1994, retroactively affirming 

that the area had met the PM10 NAAQS by the December 31, 1994 deadline established by the 1990 

amendments of the CAA (76 FR 1532; January 11, 2011) based on emissions reductions from control 

measures included in the 1993 Nogales NA SIP. EPA’s retroactive acknowledgment that the Nogales NA had 

met the NAAQS by the 1994 deadline affirms RFP milestones were met. 

In 59 FR 41998 (August 16, 1994) EPA stated that if such a border area failed to achieve RFP 

milestones reductions in PM10 emissions from sources within the U.S., then contingency measures would be 

required.48 Because RFP milestones were met in the Nogales NA, contingency measures are not required. 

In the same Federal Register notice, EPA also stated that if the area fails to obtain the emission 

reductions necessary to demonstrate attainment of the NAAQS "but for" emissions emanating from 

outside the U.S., contingency measures would not be required. 

 As demonstrated by Chapter 4 and the supporting analyses almost all of the observed exceedances 

of the PM10 standard are due to emissions from Mexico. Paving projects completed in the Nogales NA by 

the City of Nogales and Santa Cruz County have gone beyond what RFP milestones would have been 

required if the area had not met the NAAQS by the 1994 attainment date. Consistent with the EPA guidance 

cited above, the State is not including contingency measures or RFP milestones in this plan. 

 

48 59 FR 41998 (August 16, 1994). "State Implementation Plans for Serious PM10 Nonattainment Areas, and Attainment Date Waivers for 

PM10Nonattainment Areas Generally; Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act 

Amendments of 1990."
47

7.0 TRANSPORTATION CONFORMITY PROCEDURES AND MOTOR VEHICLE 

 EMISSIONS BUDGET 

 Transportation conformity is a federal regulatory process that ensures coordination and 

consistency between transportation and air quality planning. The Clean Air Act (CAA) prohibits federal 

agencies from approving or funding transportation projects if they are not consistent with State air quality 

plans. Conforming to a SIP ensures that transportation projects are consistent with a SIP and do not delay 

attainment or cause violations of the PM10 standards in the nonattainment area. The Transportation 

Conformity Rule (40 CFR Part 93) also requires States to develop a limit or “budget” for on-road mobile 

source emissions in the nonattainment area. The motor vehicle emissions budget (MVEB) ensures that 

emissions associated with transportation projects will not result in an exceedance of the NAAQS. 

Transportation plans and programs produced by the transportation planning process are required to result 

in on-road emissions that are within the budget. 

 Normally, States are required to consult with local metropolitan planning organizations (MPOs) 

when developing a MVEB. The Nogales NA does not have an MPO. To develop the MVEB, ADEQ 

consulted with EPA and the Arizona Department of Transportation (ADOT). The State chose 2011 as the 

year for the MVEB. 

EPA’s new MOVES2010 (MOVES) emissions model for onroad mobile sources was used to 

estimate the on-road motor vehicle portion of the 2011 MVEB. MOVES is used to estimate tailpipe 

emissions from cars, trucks, motorcycles, buses, as well as brake and tire wear. EPA based MOVES on 

analyses of millions of emission test results, considerable advances in EPA’s understanding of vehicle 

emissions, emissions reductions associated with new fleets of cleaner vehicles, and cleaner fuel 

specifications. 

 EPA ran the MOVES model for 2011 to produce countywide estimates for onroad mobile 

sources. The estimates were then scaled to the Nogales NA based on Census Bureau population data. To 

be conservative and to reflect the most current population data, a 0.569 ratio was used to allocate 

countywide emissions to the Nogales NA instead of the 0.551 ratio used for 2008 population-based 

allocations. Vehicular emissions calculated using MOVES account for just 1.4 percent of the Nogales NA 

2011 projected year inventory and 1.7 percent of the MVEB. 

 

 The Federal Highway Administration's Highway Statistics statewide series data on Arizona 

shows a decline in Vehicle Miles Traveled (VMT) between 2007 and 2008, and no change in VMT 

between 2008 and 2009. This trend is consistent with economic conditions. Emission inventory estimates 

for 2011 show a slight decrease in VMT. While emissions from vehicles are insignificant in terms of the 

annual inventory, ADEQ is nevertheless including these categories in the MVEB for the Nogales NA. 

 Fugitive emissions from paved and unpaved roads are affected by the number of vehicle miles 

traveled (VMT), silt volume on paved roads, and other local factors. Emissions estimates for these 

categories were based on data obtained from State and federal agencies for the 2008 NEI. Estimates for 

Santa Cruz County were then apportioned to the Nogales NA based on population. The 2011 PM10 motor 
48

vehicle emissions budget for the Nogales NA was calculated to be 1,274.3 tons per year (tpy). Once EPA 

finds this budget adequate and/or approves the budget, ADOT and FHWA must use these budgets in 

transportation conformity determinations after the effective date of the approval or adequacy finding, 

whichever is earlier. 

As established by the technical demonstrations in Chapter Four, emissions from Mexico are 

responsible for PM10 exceedances recorded in the Nogales NA. The emissions inventories in Chapter 

Three, based on estimates from EPA's 2008 National Emissions Inventory (NEI), cite road construction 

dust as the second-highest emissions source. The 2008 NEI estimates for road construction in the Nogales 

NA were based on statewide housing starts in a 2006 FHWA report when the housing market was robust, 

not actual conditions in the Nogales NA in 2008. A statewide estimate was then allocated to the county 

level based on population. As discussed in Chapter One, population growth in the Nogales NA has been 

low in recent years, much lower than other areas in the State where housing starts were thriving. 

 In addition, there have been no substantial road construction projects in the Nogales NA in the 

last five years and no projects are planned for the next five years; therefore, estimates for this category 

present a conservative worst-case scenario, not actual emissions.49

Table 7.1 

2011 Nogales NA Motor Vehicle Emissions Budget 

Sector PM10 tpy 

Dust – Unpaved Road Dust 864.9 

Dust – Paved Road Dust 121.4 

Dust – Road Construction 267.0 

Mobile – Gasoline and Diesel 

(including Exhaust, Brake and Tire Wear) 21.0 

2011 MVEB 1274.3 

Source: 2011 PM10 Emissions Inventories for the Nogales NA, 

Santa Cruz County, Arizona (see Appendix B). 

 

49 Email, Beverly Chenausky, Arizona Department of Transportation. June 25, 2012. 
49

8.0 SUMMARY & CONCLUSIONS 

 The Nogales NA was designated as nonattainment following the 1990 amendments to the CAA, 

when all areas where violations of the PM10 NAAQS had been recorded were designated nonattainment for 

PM10 by operation of law and classified “moderate” upon enactment of the Amendments. The October 1987 

PM10 emissions inventory for the Nogales NA estimated PM10 emissions on both sides of the U.S.-Mexico 

border. The 1987 emissions inventory estimated that 94 percent of PM10 emissions in Ambos Nogales are 

from Mexico, primarily from unpaved roads.50 

ADEQ followed EPA guidance to select RACM/RACT for inclusion in 1993 Nogales NA SIP. 

These measures resulted in emissions reductions sufficient to meet the PM10 NAAQS by the December 31, 

1994 deadline established by the 1990 amendments to the CAA, (See 76 FR 1532, January 11, 2011). A 

period of attainment followed through 1998, but the Nogales NA soon relapsed back into a pattern of 

intermittent exceedances of the NAAQS that has endured.

 An analysis of the monitoring data from 1985-2010 demonstrates ambient concentrations fluctuate, 

based on activity in Nogales, Sonora, Mexico. The Nogales NA did not meet the NAAQS based on 

monitoring data from 2008-2010; preliminary data indicate exceedances of the NAAQS in 2011 were 

recorded in the Nogales NA. The population of the Nogales Municipality, Sonora, is approximately 10 times 

the population of Nogales, Arizona, as shown in Figure 8.1, and rapid growth is projected to continue. 

Figure 8.1

Comparison of Ambos Nogales Population Growth 1995-2010

0

50

100

150

200

250

Thousands

Nogales Municipality, Sonora 133,491 159,878 193,517 220,292

Nogales, Arizona 20,184 20,878 20,421 20,837

1995 2000 2005 2010

Source: U.S. Census Bureau and INEGI. 

 

50 Engineering Science. "PM10 Emissions Inventory Data for the Nogales Planning Area." October, 1987. 

See Appendix C of ADEQ's 1993 Nogales NA PM10 SIP:

<http://www.azdeq.gov/environ/air/plan/download/nogpm10sip_061993.pdf>
50

A nonattainment area meets the national ambient air quality standard for PM10 when the expected 

number of days per calendar year with a twenty-four hour average concentration above 150 μg/m3 are less 

than or equal to one. To determine that the Nogales NA has met the PM10 standard “but for” emissions from 

Mexico, the State’s Section 179B analysis must show that no more than three exceedances of the standard in 

a recent consecutive three-year period were due to sources within the Nogales NA and all other exceedances 

were caused by sources originating from across the international border. This analysis found that 27 of 29 

exceedance days were due to transport of PM10 emissions from sources on the Nogales, Sonora side of the 

international border. Consequently, when considering the remaining two exceedances, the expected annual 

exceedance rate for 2007-2009 is 0.7 exceedances per year. Since the annual expected exceedance rate is 

less than one, the State has demonstrated that the Nogales NA would attain the PM10 NAAQS “but for” 

PM10 emissions originating in Mexico. 

The 2008 base year emissions inventory showed emissions from unpaved roads are still the largest 

emission source in the Nogales NA. Because the significant sources have not changed since the 

implementation of RACM/RACT required by the 1993 Nogales NA SIP, ADEQ determined those measures 

are still appropriate for the Nogales NA. Local paving/double-chip sealing projects implemented in the City 

of Nogales and the Rio Rico area within the Nogales NA have resulted in an estimated 185.5 tons of PM10

reduced, annually (see Appendix E.) 

8.1 Commitments 

 Section 110(a)(2)(A) of the CAA requires that States provide for enforceable emissions limitations 

and other control measures, means, or techniques, as well as schedules for compliance with the PM10

NAAQS. ADEQ commits to enforce the measures in this plan to attain the 24-hour average PM10 NAAQS 

for the duration of this plan. 

 ADEQ commits to continue to operate the monitors in the Nogales NA area according to the 

references and guidelines referenced below for the duration of this plan. 

 40 CFR Part 50, Appendix J, Reference Method for the Determination of Particulate Matter 

as PM10 in the atmosphere; 

 40 CFR Part 50, Appendix K, Interpretation of the National Ambient Air Quality Standards 

for particulate matter; and 

 40 CFR Part 58, Appendix A, Quality Assurance Requirements for SLAMS 

 Section 2, Quality System Requirements 

 Section 3.3 and 3.4.1, Data Quality Assessment Requirements 

 Section 4.2, Annual Reports 

 Appendix D, Section 2.8, Particulate Matter Design Criteria for SLAMS 

 Appendix E, Probe and Monitoring Path Siting Criteria for Ambient Air Quality 

Monitoring, Section 8, Particulate Matter. 
51

8.2 Conformity Commitments 

 ADEQ commits to work with ADOT and federal agencies, federal grant recipients, and federal licensees 

and permittees in the Nogales NA to ensure that requirements in CAA Sections 118 and 176 and Title 40 C.F.R. 

§ 93 Subparts A and B will be met for applicable projects requiring federal funding and/or approval. 

8.3 CAA Section 189 Continuing Commitments 

 ADEQ commits to continue to fulfill the permitting requirements of the CAA Section 189. This 

commitment will ensure that all new sources and modifications to existing sources in the Nogales NA are 

subject to preconstruction review and permitting. All new major sources and major modifications to existing 

major sources in the Nogales NA are subject to the New Source Review provisions, including New Source 

Review.