Final 

2012 State Implementation Plan 

Nogales PM10 Nonattainment Area 

July 23, 2012 

 
This page is intentionally blank. 
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 that 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 during 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 2.3 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 by 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

 

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

1999 184 184 152 119 83 15.5

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 filter-based 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, 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 

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

 

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. 

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

Appendix A). 
 

17

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.
 

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 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 continuously operating Beta Attenuation Monitor 

(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., that contingency measures would 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 Federal Highway Administration 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. 
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 
This page is intentionally blank. 
Clean Air Act, Section 179B Attainment Determination 

for the Nogales, Arizona PM10 Nonattainment Area 

U.S. Environmental Protection Agency 

Region 9 

Draft Final: July 20, 2012
2

Table of Contents 

1.0 Introduction 

 1.1 Purpose 

1.2 Sources of PM10

 1.3 Geography of the Ambos Nogales Area 

2.0 Statutory Requirements, EPA Guidance, and Attainment Standard 

2.1 Statutory Requirements 

2.2 EPA Guidance 

2.3 Guidance for Determining Attainment of the PM10 NAAQS

3.0 Review of Data and Analyses 

3.1 Population Estimates 

3.2 Emissions Inventories 

3.2.1 Nogales, Arizona Emissions Inventory Estimates 

3.2.2 Nogales, Sonora Emissions Inventory Estimates 

 3.2.3 Review and Comparison 

3.3 Ambient PM10 Levels, Topography, and Meteorological Data 

 3.3.1 Analyses of 2007-2009 Exceedance Days 

 3.3.2 Review of 2010 and 2011 Exceedance Days 

4.0 Findings

4.1 A Conceptual Model of 2007-2009 Exceedance Days 

4.2 Review of Exceedance Days That Diverge From the Conceptual Model 

4.2.1 January 1, 2007 Exceedance Day Review 

 4.2.2 January 26, 2008 Exceedance Day Review 

 4.2.3 May 22, 2008 Exceedance Day Review 

 4.2.4 January 1, 2009 Exceedance Day Review 

4.3 Estimate of Expected Exceedance Days “But For” International Transport 

 4.3.1 Daily Analysis 

 4.3.2 Hourly Analysis 

5.0 Conclusion 
3

List of Figures 

Figure 1: Map of Ambos Nogales Area and Nogales, Arizona PM10 Nonattainment Area 

Figure 2: Elevated Topographical View of Ambos Nogales Area from Northwest 

Perspective with Nogales, Sonora Highlighted and International Border in Red Line. 

Figure 3: Average hourly PM10 concentration, wind speed, and temperature at the 

Nogales, Arizona Post Office FEM monitor versus time of day for all exceedances, 

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

Figure 4: January 1, 2007 PM10 Concentrations and wind speeds compared to average 

PM10 concentrations and windspeeds from Figure 3. 

Figure 5: January 26, 2008 PM10 concentrations and wind speeds compared to average 

PM10 concentrations and windspeeds from Figure 3. 

Figure 6: May 22, 2008 PM10 concentrations and wind speeds compared to average PM10

concentrations and windspeeds from Figure 3. 

Figure 7: January 1, 2009 PM10 concentrations and wind speeds compared to average 

PM10 concentrations and windspeeds from Figure 3. 

List of Tables 

Table 1: 2010 Population: Nogales NAA, Arizona and Nogales Municipality, Mexico 

Table 2: Nogales, Arizona Exceedances of 24-hour NAAQS From 1995 - 2000 with 

1995 and 2000 Ambos Nogales Population Data. 

Table 3: Nogales, Arizona Exceedances of 24-hour NAAQS From 2000 - 2010 with 

Ambos Nogales 2000, 2005, 2010 Population Data. 

Table 4: 2008 Nogales NAA PM10 Emissions Inventory (tons per year) 

Table 5: PM10 Emissions Inventory for Nogales Municipality for 2008 and 2011 (Tons)

Table 6: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year). 

Table 7: 2011 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year). 

Table 8: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year). 

Table 9: 2011 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year). 

Table 10: Percentage of observed PM10 concentrations attributable to wind direction; 

January 1, 2007, May 22, 2008, and January 1, 2009 are excluded from the analysis of 

exceedance days. 

Table 11: Hourly ambient PM10 concentrations sorted by concentration and wind 

direction, 2007-2009 exceedance days 

Table 12: 2007-2009 Exceedance Days Concentration Values Disaggregated by 

Southerly Wind Quadrant versus All Other Wind Directions ( g/m3

).

Table 13: January 1, 2007 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant. 

Table 14: January 26, 2008 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant. 
4

Table 15: May 22, 2008 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant. 

Table 16: January 1, 2009 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant. 

Appendices 

Appendix A: 2008 and 2011 Emissions Inventories for Nogales NAA 

Appendix B: 2008 and 2011 Emissions Inventories for the Nogales Municipality, 

Sonora, Mexico 

Appendix C: Analysis of Ambient PM10 Levels, Topography, and Meteorological Data 

in Nogales, Arizona: 2007 - 2009
5

1.0 Introduction 

1.1 Purpose 

This document reviews and integrates several analyses of PM10 pollution in and around 

Nogales, Arizona to determine if the Nogales nonattainment area would have attained the 

National Ambient Air Quality Standard (NAAQS) for PM10 but for sources of PM10 in 

nearby Nogales, Sonora, Mexico. The Arizona Department of Environmental Quality 

(ADEQ) requested that EPA provide this analysis to support ADEQ’s work on a PM10

State Implementation Plan (SIP) for the Nogales nonattainment area (NAA), located in 

Santa Cruz County, Arizona. 

1.2 Sources of PM10

PM10 refers to particulate matter of ten microns or less in aerodynamic diameter. Another 

class of particles, denoted as PM2.5, also called fine particulate, refers to particles of 2.5 

microns or less in aerodynamic diameter. PM10 includes both PM2.5 and the particulates 

with aerodynamic diameter between 2.5 and 10 microns. Sometimes referred to as PM2.5-

10, this larger fraction of particles between 2.5 and 10 microns is also called “coarse” 

particulate. While fine particles originate mostly from combustion sources and secondary 

aerosol generation processes, coarse particles usually originate from mechanical activities 

and fugitive source categories. Typical sources of PM10 include fugitive dust, open 

burning including wild fires, mineral crushing and grinding operations, agricultural 

activities such as land tilling, dust suspended from vehicle travel on paved and unpaved 

roads and, to a lesser extent, fuel combustion sources and mobile source exhaust. 

1.3 Geography of the Ambos Nogales Area 

 

The combined communities of Nogales, Arizona and Nogales, Sonora, or Ambos 

Nogales are located within the Sonoran Desert. This desert covers 120,000 square miles 

with a minimum elevation of 2,500 feet and is in the Basin and Range topographic 

province. This topography is characterized by north-south elongated valleys surrounded 

by mountain ranges. Ambos Nogales is located in such a north-south valley created by 

the Nogales Wash running north to the Santa Cruz River. 

 

From south to north, Nogales Municipality is roughly analogous to a United States (U.S.) 

county and covers a 632.5 square mile area along the U.S./Mexico border.1 The largest 

urban center in the municipality is the City of Nogales, Sonora. Nogales, Sonora, Mexico 

lies directly south of Nogales, Arizona across the international border. Collectively 

referred to as Ambos Nogales, the cities of Nogales, Arizona and Nogales, Sonora, 

Mexico comprise the largest international border community in Arizona, with a combined 

population of 232,550 inhabitants in 2010.2 The majority of the population within the 

Nogales Municipality lives within the city of Nogales, Sonora. The mean elevation 

 

1

 Nogales Municipality land area was calculated by EPA using GIS software. 

2

 Nogales, Arizona had 20,017 inhabitants and Nogales, Sonora, Mexico had 212,533 inhabitants. U.S. 

Census Bureau 2010 and Instituto Nacional de Estadistica Geografia e Informatica, (INEGI) 2010.
6

above sea level in Nogales, Sonora is 4,265 feet.3 At 5,380 feet, the highest elevation 

area in Nogales, Sonora is in the Cerro de los Nogales (Nogales Hill), west of where the 

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

Proceeding northward, the U.S. and Mexico border forms the southern boundary of the 

Nogales NAA and Santa Cruz County, Arizona. Near the center of the Nogales NAA, 

the city of Nogales, Arizona is sixty miles south of Tucson, Arizona in the middle and 

southernmost portion of Santa Cruz County. The city of Nogales, Arizona is the largest 

city in the 76.1 square mile nonattainment area.4 The mean elevation above sea level in 

Nogales, Arizona is 3,865 feet. Mountain ranges near Nogales include the Patagonia 

Mountains to the east and the Tumacacori, Atascosa, and Pajarito mountains to the west. 

Approximately 25 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. 

 

3

 “Statistical Municipal Workbook for Nogales, Sonora”, 2005 edition, INEGI. 

4

 Nogales NAA land area was calculated by EPA using GIS software. 
7

Figure 1: Map of Ambos Nogales Area and Nogales, Arizona PM10 Nonattainment Area 
8

2.0 Statutory Requirements, EPA Guidance, and Attainment Standard 

Because the Nogales NAA lies along the international border with Mexico, there are 

specific statutory requirements in the Clean Air Act (CAA) that apply to the Nogales 

NAA. With a demonstration showing that the Nogales NAA would have attained the 

PM10 NAAQS but for international sources of PM10, EPA may approve an attainment 

plan provided by the State. Such a “but for” attainment demonstration, however, must be 

consistent with statutory and regulatory requirements. First, we review the statutory basis 

for a “but for” attainment demonstration. Secondly, we will review EPA’s published 

guidance on how such an analysis may be structured. Lastly, we will review the 

attainment standard applied to PM10 nonattainment areas, as stipulated in federal 

regulations. 

2.1 Statutory Requirements 

The Nogales NAA shares its southern border with Mexico. For international border 

areas, the Clean Air Act (CAA) section 179B(a) states that: 

“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 chapter 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 chapter, 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.”

As stated above, notwithstanding any other provision of law, should Arizona establish to 

the satisfaction of the EPA Administrator that the Nogales NAA would have attained the 

PM10 NAAQS by the applicable attainment date but for emissions emanating from 

outside the United States (U.S.), then the Nogales NAA shall not be subject to the 

provisions of CAA section 189(a)(1)(b), requiring a demonstration of attainment of the 

PM10 standard by the applicable attainment date. 

Section 179B(d) goes on to state that should Arizona provide a demonstration showing 

that the Nogales NAA would have attained the PM10 NAAQS but for emissions 

emanating from outside the U.S., then the Nogales NAA shall not be subject to the 

provisions of CAA section 189(b)(2), as well, and should not be reclassified as a 

“serious” PM10 nonattainment area. 
9

2.2 EPA Guidance 

EPA has issued guidance relating to serious PM10 nonattainment areas (General 

Preamble); this guidance includes a discussion of the requirements applicable to 

international border areas.5 The General Preamble reviews the information and methods 

that may be used to determine if an international border area qualifies for treatment under 

CAA section 179B and to demonstrate that the area would attain the relevant NAAQS 

but for emissions emanating from outside the U.S. 

The General Preamble provides that “several types of information may be used to 

evaluate the impact of emissions emanating from outside the U.S.” The EPA will 

consider the information “for individual nonattainment areas on a case-by-case basis in 

determining whether an area may qualify for treatment under section 179B.” The 

General Preamble suggests five methods that may be used to determine the impact of 

emissions emanating from outside the U.S. and states that “the State may use one or more 

of these types of information or other techniques, depending on their feasibility and 

applicability, to evaluate the impact of emissions emanating from outside the U.S. on the 

nonattainment area.” Below, we discuss the five methods and their applicability to the 

Nogales NAA. 

Method 1: Place several ambient PM10 monitors and a meteorological station measuring 

wind speed and direction in the U.S. nonattainment area near the international border. 

Evaluate and quantify any changes in monitored PM10 concentrations with a change in 

the predominant wind direction. 

We reviewed the ambient PM10 data, meteorology, and topography in the Ambos Nogales 

area. The State of Arizona maintains a monitor in Nogales, Sonora, as well as, three 

monitors in Nogales, Arizona. The Nogales, Arizona monitors are divided as follows: 

two monitor’s measure ambient PM10 levels; and, one monitor measures ambient PM2.5

levels. Arizona also has two reference monitors at increasing distances from the Nogales 

NAA. Our analysis of the ambient data, meteorology, and topography is provided in 

Appendix C and is discussed below in Section 3.3. 

Method 2: Comprehensively inventory PM10 emissions within the U.S. in the vicinity of 

the nonattainment area and demonstrate that those sources, after application of reasonably 

available controls, do not cause the NAAQS to be exceeded. This analysis must include 

background PM10 in the area. Estimates of background PM10 levels could be based on 

concentrations measured in a similar area not influenced by emissions from outside the 

U.S. 

This method implies the use of an air quality model to demonstrate that emissions within 

the U.S. do not create a violation of the NAAQS. Although a comprehensive, area-wide 

 

5

“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 41998, August 16, 1994. 
10

inventory of PM10 emissions is available for Nogales, Arizona, information about the 

spatial and temporal distribution of those emissions required to support air quality 

modeling is not readily available and would require significant effort to develop. 

Furthermore, given the complex topography of the Ambos Nogales area, it would be a 

challenging and expensive task to develop an adequate demonstration using available 

modeling tools. 

Method 3: Analyze ambient sample filters for specific types of particles emanating from 

across the border. Although not required, characteristics of emissions from sources may 

be helpful so as to better demonstrate the causal relationship with and contribution to 

exceedances in the U.S. nonattainment area due to domestic and international sources. 

This method is unlikely to produce useful information for Nogales because the large 

proportion of crustal PM sources on either side of the international border would far 

outweigh any specific stationary or combustion-based PM source contribution that may 

be discerned by a filter-based analysis. Also, we did not have specific local and 

international point source emissions information, such as source specific signature 

emissions compounds, with which to correlate the filter analyses results that Arizona 

might have provided. 

Method 4: Inventory the sources on both sides of the border and compare the magnitude 

of PM10 emissions originating within the U.S. to those emanating from outside the U.S. 

We produced two emissions inventories: the first inventory describes the PM10 sources 

in and around Nogales NAA, Arizona; and, the second inventory describes the PM10

sources in and around Nogales, Sonora, Mexico. Our Nogales NAA, PM10 Emissions 

Inventory is provided in Appendix A and our Nogales Municipality, Sonora, Mexico 

Emissions Inventory is provided in Appendix B. The results of both inventories are 

discussed below in Section 3.2. Also, as a basis for these analyses, we reviewed 

population estimates and will examine relative population differences in Section 3.1. 

Method 5: Perform air dispersion and/or receptor modeling to quantify the relative 

impacts on the nonattainment area of sources located within the U.S. and of foreign 

sources of PM10 emissions. 

As discussed above, the information necessary to support air dispersion or receptor 

modeling is not readily available for the Nogales, Arizona area, nor is it available for the 

Nogales, Mexico area. For example, we did not have available a gridded emissions 

inventory or a data set from an extensive monitoring array of ambient PM10 values and 

meteorological data derived from observations on multiple exceedance days. 

We considered a backward wind trajectory analysis using the HYSPLIT model, based on 

Eta Data Assimilation System (EDAS) gridded meteorological data, but did not pursue 

this analysis.6 Previously, we performed such an analysis for the Nogales, Arizona area 

 

6

 The HYSPLIT model refers to the “Hybrid Single Particle Lagrangian Integrated Trajectory” model 

developed and maintained by the National Oceanic and Atmospheric Administration. 
11

and found the resulting wind trajectories to be inconclusive. The EDAS has a 40- 

kilometer grid resolution; in contrast, the valley containing Nogales is 20 kilometers wide 

at its widest point. As a result, the EDAS data were not resolved enough to portray the 

south-to-north valley air drainage flows that are a key feature of local Nogales 

meteorology; consequently, we rejected further use of HYSPLIT model for purposes of 

this Section 179B analysis. 

To summarize, we analyzed ambient PM10 levels in and around the Nogales NAA, the 

local meteorology associated with exceedances of the PM10 standard, and sources of 

PM10 emissions on either side of the international border. These analyses are consistent 

with Methods 1 and 4 described by the General Preamble. We examined Method 3, but 

did not pursue this avenue of investigation because it was unlikely that we would get 

definitive results given the large crustal source emissions on either side of the 

international border. 

Initially, we did not pursue Methods 2 and 5 because we did not have the data and the 

models required for this type of analysis. Instead, we used the information at hand and, 

consistent with methods 1 and 4, determined if the Nogales NAA would have attained the 

standard, but for international emissions. Should these less resource intensive methods 

have proved inconclusive, we would have considered further analyses consistent with 

Methods 2 and 5. 

As stated in the General Preamble, the EPA will consider the information “for individual 

nonattainment areas on a case-by-case basis in determining whether an area may qualify 

for treatment under section 179B.” Because the individual circumstances surrounding a 

nonattainment area may differ widely whether by data, resources, or emissions sources, 

EPA anticipates that “the State may use one or more of these types of information or 

other techniques, depending on their feasibility and applicability, to evaluate the impact 

of emissions emanating from outside the U.S. on the nonattainment area.” The analysis 

provided below for the Nogales NAA is specific to this nonattainment area only and the 

timeframe, data, and circumstances therein. 

2.3 Guidance for Determining Attainment of the PM10 NAAQS 

EPA determines whether an area's air quality is meeting the PM10 NAAQS based upon 

air quality data gathered at monitoring sites in the nonattainment area. Then, EPA 

reviews the data to determine the area's air quality status according to 40 CFR part 50, 

appendix K (the Attainment Guidance). Three consecutive years of clean air quality data 

(i.e., no more than one expected exceedance per year) is generally needed to show 

attainment of the twenty-four hour PM10 standard. As defined by 40 CFR part 50, 

appendix K, a complete year of air quality data is composed of all four calendar quarters 

with each quarter containing data from at least 75 percent of the scheduled sampling 

days. 

Under the Attainment Guidance, a nonattainment area meets the twenty-four hour PM10

NAAQS when the expected number of days per calendar year with a twenty-four hour 
12

average concentration above 150 micrograms per cubic meter (μg/m3) is equal to or less 

than one. In general, the number of expected exceedances at a site which samples every 

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

averaging them over the most recent three calendar years. For sites which do not sample 

every day, EPA requires adjusting the observed exceedances to account for days not 

sampled. The procedures for making this data adjustment are specified in 40 CFR part 

50, appendix K. 

For this review of the Nogales NAA and the contribution of international emissions, we 

are analyzing ambient air quality data from 2007-2009 as representing the most recent 

and complete three-year data set certified by Arizona. The 2010 data set is incomplete 

and the 2011 data set has yet to be submitted to EPA and certified as meeting the relevant 

quality control and quality assurance requirements. The standard we will use to 

determine attainment of the PM10 NAAQS, “but for” international emissions, is similar to 

the one described above: the expected number of days per calendar year with a twentyfour hour average concentration above 150 μg/m3 must be equal to or less than one. To 

determine that the Nogales NAA has met the PM10 standard “but for” emissions from 

Mexico, the analysis must show that no more than three exceedances, based on data 

completeness and every day sampling, in the 2007-2009 analysis period were caused by 

emission sources on the U.S. side of the border. 

3.0 Review of Data and Analyses 

In this section, we review the relevant data and observations taken from the following 

supporting analyses described in Section 2.2: 

 

2008 and 2011 Emissions Inventories for the Nogales NAA; 

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.

These analyses are summarized here and provided in their entirety within the appendices 

of this document. 

3.1 Population Estimates 

In producing emissions inventories, we reviewed recent 2010 population information 

from the U.S. Census Bureau and Mexican Census data from the Instituto Nacional de 

Estadistica Geografia e Informatica (INEGI). While population estimates, by themselves, 

are not proximal indicators of emissions activity, these estimates provide an indication of 

relative human activity and resulting PM10 emissions on either side of the international 

border. 

 
13

Table 1: 2010 Population: Nogales NAA, Arizona and Nogales Municipality, Mexico 

Area Population Percent

Nogales NAA, Arizona 24,059 9.8%

Nogales Municipality, Mexico 220,292 90.2%

Total 244,351 100%

Although the Nogales Municipality is a larger land area than the Nogales NAA, a large 

proportion of Municipality’s population is concentrated within the City of Nogales, 

Sonora and the surrounding area. In sum, 90.2 percent of the 2010 population in the 

Ambos Nogales area can be attributed to the Mexican side of the international border. 

We also examined population change since 1995, when the Nogales NAA had met the 

PM10 NAAQS.7 Below, Tables 2 and 3 show population estimates for 1995, 2000, 2005, 

and 2010 beside the annual number of expected exceedances since 1995. 

Table 2: Nogales, Arizona Exceedances of 24-hour NAAQS From 1995 - 2000 with 

1995 and 2000 Ambos Nogales Population Data. 8

1995 1996 1997 1998 1999 2000

Expected Exceedances:

1 in 6 day monitoring 0.0 0.0 0.0 13.5 15.5 0.0

Continuous monitoring* --- --- --- --- --- ---

Population:

Nogales, Arizona 20,184 --- --- --- --- 20,878

Nogales Municipality 133,491 --- --- --- --- 159,787

*Continuous monitoring started in 2005; see table below.

Source for expected exceedance data: Air Quality System Database.

Source for 1995 and 2000 population data: INEGI & U.S. Census.

Table 3: Nogales, Arizona Exceedances of 24-hour NAAQS From 2000 - 2010 with 

Ambos Nogales 2000, 2005, 2010 Population Data. 

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Expected Exceedances:

1 in 6 day monitoring 0.0 6.9 6.1 12.3 0.0 17.9 20.0 6.1 6.6 0.0 0.0

Continuous monitoring --- --- --- --- --- 29.6 47.9 14.0 13.2 2.0 8.5*

Population:

Nogales, Arizona 20,878 --- --- --- --- 20,421 --- --- --- --- 20,837

Nogales Municipality 159,787 --- --- --- --- 193,517 --- --- --- --- 220,292

* There were no quarters in 2010 where there was a complete data set per 40 CFR part 50, appendix K; see 

Section 3.3.2 for discussion of 2010 data. 

Source for expected exceedance data: Air Quality System Database.

Source for 2000, 2005, and 2010 population data: INEGI & U.S. Census. 

 

7

 76 FR 1532, January 11, 2011. 

8

 The 1995 Nogales, Arizona population estimate was interpolated from 1990 and 2000 U.S. Census 

figures; 1990 population was 19,489. 
14

Between 1995 and 2010, Nogales Arizona population has increased slightly, 

approximately 3 percent, and has fallen since 2000. In contrast, the Nogales 

Municipality, Sonora population has increased 65 percent in the 1995-2010 timeframe. 

With exceptions of 2000 and 2004, exceedances of the PM10 standard have been recorded 

since 1997. The largest number of exceedances, 47.9, was recorded in 2006. 

3.2 Emissions Inventories 

Starting with information from EPA’s 2008 National Emissions Inventory for Santa Cruz 

County, Arizona, we estimated 2008 and 2011 emissions inventories for the Nogales 

NAA.9

 Unfortunately, we did not have a readily available and comparable PM10

emissions data collection system from which to draw from when estimating emissions for 

the Nogales Municipality, Mexico. Consequently, using the best information publically 

available at the time of our analysis, we estimated and calculated a source-based 

emissions inventory for the Nogales Municipality based primarily on data and 

methodologies from the 1999 Mexico National Emissions Inventory and a subsequent 

update providing a 2012 Mexico emissions inventory.10

 Because there was a reasonable 

range of data inputs from which to select in estimating PM10 emissions, particularly for 

emissions from unpaved and paved roads, we calculated a low and high estimated range 

of PM10 emissions for the Nogales Municipality. 

3.2.1 Nogales NAA, Arizona Emissions Inventory Estimates 

As shown in Table 2 below, in 2008 the majority of PM10 emissions in the Nogales NAA 

came from fugitive dust from four source categories: unpaved road dust, road 

construction, commercial/industrial/institutional construction, and paved road dust. Our 

estimated emissions inventory for 2011 only differed slightly as total emissions decreased 

from 1,531 tons per year (tpy) in 2008 to 1,528 tpy in 2011, due primarily to new and 

cleaner engine standards for diesel engines. From 2008 to 2011, the emissions estimated 

for five of the top six source categories remain unchanged, except for residential wood 

burning which increases two tons per year. Again, as in 2008, these six source categories 

account for approximately 95 percent of all PM10 emissions in the Nogales NAA in 2011. 

 

9

 See Appendix A: 2008 and 2011 Emissions Inventory for Nogales NAA. 

10 These two primary source documents are as follows: “Mexico National Emissions Inventory, 1999: Six 

Northern States”, Final, April 30, 2004, prepared by Eastern Research Group (ERG), Acosta Y Asociados, 

and Transengineering, for the Secretariat of the Environment and Natural Resources and the National 

Institute of Ecology of Mexico, the United States Environmental Protection Agency, the Western 

Governors’Association, and the North American Commission for Environmental Cooperation. (1999 

Mexico NEI); and, “Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 

2030”, Final, January 9, 2009, prepared by Eastern Research Group, Inc. (ERG) for the Instituto Nacional 

de Ecologia, Mexico City, Mexico, the National Renewable Energy Laboratory, and the United States 

Environmental Protection Agency, with assistance from the Western Governors’ Association. (2008-12 

NEI Projections). See Appendix B: 2008 and 2011 Emissions Inventories for the Nogales Municipality, 

Sonora, Mexico for the complete discussion of the sources and methods use to develop this emissions 

inventory. 
15

Table 4: 2008 Nogales NAA PM10 Emissions Inventory (tons per year)11

Source Category PM10 Percent

Dust - Unpaved Road Dust 865 56.5%

Dust - Road Construction 267 17.4%

Dust - Commercial/Industrial/Institutional Construction 143 9.3%

Dust - Paved Road Dust 121 7.9%

Fuel Combustion - Residential – Wood 24 1.6%

Dust - Residential Construction 24 1.6%

Waste Disposal - Residential Garbage Burning 23 1.5%

All other sources 64 4.2%

Total 1,531 100%

Note: All other sources include emissions from source categories such as all on-road mobile and off-road 

mobile, all commercial and industrial fuel combustion, agriculture, land clearing and burning activities. 

3.2.2 Nogales, Sonora, Mexico Emissions Inventory Estimates 

While less detailed than the Nogales NAA, Arizona emissions inventory, the Nogales, 

Sonora emissions inventory shows that the largest contributing sources of PM10

emissions are unpaved and paved road dust followed by residential wood combustion and 

other area sources. While the high estimate for point sources may be unlikely, we have 

included it because we did not have readily available source-specific information 

providing a precise estimate for stationary point sources of PM10 in the Municipality. 

The methods for calculating these estimates are discussed in Appendix B. 

Table 5: PM10 Emissions Inventory for Nogales Municipality for 2008 and 2011 (tons)

Source Category Range 2008 2011

Point Sources Low Estimate 1.1 1.1

High Estimate 305 390

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

High Estimate 5,521 5,944

Paved Road 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

Emissions are rounded to the nearest ton/year, or to the nearest tenth of a ton/year for emissions less than 

10 tons/year. 

 

11

 For all tables and throughout the text, emissions are rounded to the nearest ton/year, or to the nearest 

tenth of a ton/year for emissions less than 10 tons/year. Due to rounding, totals may not reflect exactly the 

sum of each category. 
16

3.2.3 Review and Comparison 

Both the Nogales NAA and the Nogales Municipality have similar sources of PM10, 

primarily fugitive dust from unpaved and paved roads, as well as combustion sources and 

construction. A comparison of 2008 and 2011 low emission inventory estimates suggests 

that there is a 36/64 percent split in total Ambos Nogales emissions between emissions 

from the Nogales NAA, Arizona and Nogales Municipality, Mexico areas, respectively. 

To characterize the relative difference by ratio, for every one ton of PM10 emissions 

produced annually in Nogales NAA there is an estimated 1.8 tons produced in Nogales 

Municipality. 

Table 6: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,531 36.1%

Nogales Municipality, Mexico 2,713 63.9%

Total 4,244 100%

Table 7: 2011 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,528 35.7%

Nogales Municipality, Mexico 2,757 64.3%

Total 4,285 100%

Similarly, a comparison of 2008 and 2011 high emission inventory estimates suggests 

that there is an 18/82 percent split in total Ambos Nogales emissions between emissions 

from the Nogales NAA, Arizona and Nogales Municipality, Mexico areas, respectively. 

Again, to characterize the relative difference by ratio, for every one ton of PM10

emissions produced annually in Nogales NAA there is an estimated 4.6 tons produced in 

Nogales Municipality. 

Table 8: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,531 18%

Nogales Municipality, Mexico 6,987 82%

Total 8,518 100%
17

Table 9: 2011 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,528 17.1%

Nogales Municipality, Mexico 7,420 82.9%

Total 8,948 100%

To summarize, a comparison of our 2008 and 2011 emissions inventory data suggests 

that for every one ton of PM10 produced in the Nogales NAA, there were between 1.8 and 

4.6 tons of PM10 emissions produced annually in the Nogales Municipality. The 

emissions sources appear to be similar with the majority of emissions from fugitive dust 

sources, such as reintrained unpaved and paved road dust. 

3.3 Ambient PM10 Levels, Topography, and Meteorological Data 

In our review and analyses, we found that the Ambos Nogales area’s meteorology and 

topography are likely components of the observed exceedances of PM10 NAAQS and 

there is a definite south to north directional component to these exceedances; particularly, 

in reference to the international border between Nogales, Arizona and Nogales, Sonora, 

Mexico. Over the 2007-2009 timeframe, there were 29 exceedances at the Nogales, 

Arizona Post Office (Model: Met One BAM 1020) monitor. We are focusing on the data 

from this particular monitor for the following reasons: it is comparable to the NAAQS; it 

has recorded all the exceedances; it has recorded hourly ambient values; and, it has a 

sufficiently complete dataset for comparison to the NAAQS. 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. 

Our analysis of ambient concentration and meteorological data identified 26 of the 29 

exceedances as having nearly identical diurnal patterns; the three exceptions were 

January 1, 2007, May 22, 2008, and January 1, 2009.12

 For each of the 26 days, there is a 

strong pattern of decreasing PM10 concentrations in the very early morning. The majority 

of days have a pronounced PM10 increase and drop-off between 6:00 am and 9:00 am, 

suggesting a reproducible direct PM10 source, noting the times correspond to a morning 

commute pattern. The PM10 concentrations reach their lowest points between 10:00 am 

and 4:00 pm, with corresponding increases in ambient temperature and wind speed 

observed during those times. As temperatures and wind speeds drop in the evening 

hours, a pronounced spike in PM10 concentration is then observed beginning between 

4:00 pm and 6:00 pm, with concentrations remaining high for a couple of hours and 

gradually dropping off towards midnight. The afternoon spike in PM10 concentrations 

correlates with a significant drop in temperature and wind speed, and generally a shift to 

low and variable southerly (from the south) winds. 

 

12

 See, in particular, Section 3 of Analysis of Ambient PM10 Levels, Topography, and Meteorological Data 

in Nogales, Arizona: 2007 - 2009, in Appendix C. 
18

Looking at topography from south to north, the highest elevation of a primary roadway 

transect is at 4,331 feet at the southern edge of Nogales, Sonora, falling to the 

international border at 3,933 feet, continuing to the northern edge of the Nogales, Arizona 

PM10 NAA at 3,425 feet, and elevation continues to fall along the Santa Cruz River 

watershed to the north to approximately 3100 feet.13 Across this largest 48.5 mile local 

transect, the elevation falls approximately 1200 feet from south to north. 

An examination of a smaller 14.8 mile transect along a similar primary roadway route 

shows elevation declines on a south to north axis. The Nogales, Sonora sub-transect 

shows an elevation drop of 201 feet over 4.8 miles to the international border where there 

is a slight leveling; starting at 4,134 feet at the Nogales, Sonora urban boundary and 

dropping to 3,933 feet at the international border. The Nogales, Arizona sub-transect 

shows an elevation drop of 508 feet over 10 miles, from the international border to the 

northern boundary of the Nogales NAA; starting at 3,933 feet and dropping to 3,425 

feet.14 In sum, looking at a south to north transect along the Nogales Wash, elevations 

fall from south to north with the highest elevations in the Nogales, Sonora area. Looking 

at the general topography of the Ambos Nogales area (from a northwest perspective, see 

Figure 2), there is a funnel created as the Nogales Wash falls from higher southern 

elevations to the international border along the route of the Alvaro Obregón Boulevard 

and into Nogales, Arizona. Small side canyons extend off of the Nogales Wash bottom 

and into the surrounding hills between the international border and south of the Nogales, 

Sonora city center, and to a lesser extent into Nogales, Arizona as elevations drop moving 

to the north. 

 

13 See Figure 18, Long Aerial and Elevation Transect of Nogales Arizona and Nogales, Sonora; Analysis of 

Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007 - 2009, in 

Appendix C.

14 See Figure 19, Short Aerial and Elevation Transect of Nogales, Arizona and Nogales, Sonora; Analysis 

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

Appendix C.
19

Figure 2: Elevated Topographical View of Ambos Nogales Area from Northwest 

Perspective with Nogales, Sonora Highlighted and International Border in Red Line. N 

3.3.1 Analyses of 2007 - 2009 Exceedance Days 

In three analyses of ambient PM10 concentrations and wind direction on exceedance days, 

we found that high PM10 concentrations are associated with wind direction from a 

southerly quadrant, or southerly air flows more often than what is typically observed on 

non-exceedance days. Also, we found that the largest number of hourly ambient values 

above 150 g/m3and the highest ambient values, including those markedly above 

150 g/m3

, originated from a southerly wind direction quadrant. 

In the first analysis, for the 26 exceedance days with nearly identical diurnal patterns, we 

examined the percent of the total observed 24-hour concentration that is attributable to 

winds out of specific directional quadrants by performing a weighted analysis of hourly 

concentrations. The weighted hourly analysis shows that, for non-exceedance days, the 

concentrations attributable to winds from a southerly wind quadrant are approximately 62 

percent of the total observed PM10. When we examine exceedance days, however, 

concentrations attributable to wind from a southerly wind quadrant increases to 80 

percent of the total. 
20

Table 10: Percentage of observed PM10 concentrations attributable to wind direction. 

January 1, 2007, May 22, 2008, and January 1, 2009 are excluded from the analysis of 

exceedance days. 

Ambient Data Sample Northerly

(315 - 44°)

Easterly

(45 - 134°)

Southerly

(135 - 224°)

Westerly

(225 - 314°)

All Days in 2007 - 2009 11% 16% 63% 10%

Non-Exceedance Days 12% 16% 62% 10%

Exceedance Days 7% 10% 80% 3%

In the second analysis, we examined all exceedance days using pollution roses, a method 

correlating wind direction observations with hourly ambient PM10 concentrations. We 

found that higher PM10 readings were observed when wind direction was from the 

southernmost quadrant; see Table 11 below. We found that the largest proportion of 

hourly values above 150 g/m3and the highest hourly concentrations were found in the 

southerly wind direction quadrant. When ambient PM10 values above 150 g/m3 were 

sorted by 100 g/m3increments to 550 g/m3and greater, we found within each 

increment above 150 g/m3

that 71 to 92 percent of the ambient PM10 observations were 

from the southerly wind quadrant.15

 

Table 11: Hourly ambient PM10 concentrations sorted by concentration and wind 

direction, 2007 - 2009 exceedance days. 

Range of Ambient Concentration Values (microgram/m3)

Wind 

Direction 

Quadrant

< 150 150 - 250 250 - 350 350 - 450 450 - 550 >= 550

Share of All 

Wind Direction 

Observations

Northerly

NW to NNE 27% 6% 3% 3% 3% 0% 17%

Easterly

NE to ESE 15% 16% 16% 11% 3% 8% 14%

Southerly

SE to WSW 41% 71% 72% 84% 92% 92% 57%

Westerly

SW to WNW 18% 6% 8% 3% 3% 0% 12%

Total 100% 100% 100% 100% 100% 100% 100%

Finally, we examined the wind direction and hourly PM10 concentrations on each 

exceedance day to determine two average ambient values for each exceedance day: one 

value for the southerly wind quadrant and a second value representing all other wind 

directions. Table 12 below shows the results. Two exceedance days, January 1, 2007 

and January 26, 2008, have an average ambient concentration greater than 150 g/m3

for 

 

15

 The 80 percent figure in Table 10 represents concentration-weighted hours from the southerly wind 

quadrant on exceedance days; whereas, the 57 percent figure in Table 11 represents a percentage of hourly 

observations from the southerly wind quadrant on exceedance days. To explain further, while 57 percent of 

the winds are from the southerly wind quadrant on exceedance days, there are much higher concentrations 

coming from those directions. 
21

the “all other wind direction” quadrants. The ratio of the southerly quadrant 

concentration to the “all other direction” quadrant concentration ranges from 0.86 to 11, 

with an average ratio value of 3.83. Only one day, January 1, 2007, has a ratio value less 

than 1.0; i.e., the “all other direction” quadrants’ share exceeds the southerly quadrant 

share. 

Table 12: 2007 - 2009 Exceedance Days Concentration Values Disaggregated by 

Southerly Wind Quadrant versus All Other Wind Directions ( g/m3

).

Date

24-hour 

Concentration

Southerly Wind Quadrant 

Concentration

(135 to 224 degrees)

All Other Wind 

Direction 

Concentration

(225 to 134 degrees)

Concentration Ratio 

of Southerly Wind 

Quadrant to Other 

Wind Directions

1-Jan-2007 210 199 231 0.86

6-Feb-2007 180 228 100 2.28

6-Mar-2007 157 265 66 4.02

15-Mar-2007 175 360 65 5.54

19-Oct-2007 189 335 43 7.79

27-Oct-2007 210 301 133 2.26

2-Nov-2007 211 278 79 3.52

3-Nov-2007 170 213 128 1.66

4-Nov-2007 170 183 148 1.24

6-Nov-2007 186 209 119 1.76

18-Nov-2007 167 277 38 7.29

19-Nov-2007 177 216 63 3.43

28-Nov-2007 167 278 75 3.71

24-Dec-2007 233 368 45 8.18

26-Jan-2008 204 257 182 1.41

27-Feb-2008 166 251 66 3.80

18-May-2008 169 356 57 6.25

22-May-2008 217 217 No values observed ---

26-Oct-2008 156 219 53 4.13

31-Oct-2008 159 245 74 3.31

1-Nov-2008 234 369 76 4.86

8-Nov-2008 167 197 79 2.49

16-Nov-2008 171 273 69 3.96

17-Nov-2008 206 297 27 11.00

20-Nov-2008 161 225 56 4.02

22-Nov-2008 179 245 102 2.40

31-Dec-2008 155 163 117 1.39

1-Jan-2009 238 323 119 2.71

16-Jan-2009 204 247 119 2.08
22

To summarize, we analyzed hourly ambient values on exceedance days in three different 

ways. We found that high PM10 concentrations are associated with wind direction from a 

southerly quadrant, or southerly air flows more often than what is typically observed on 

non-exceedance days. We found that the largest number of hourly ambient values above 

150 g/m3and the highest ambient values, including those markedly above 150 g/m3, 

originated from a southerly wind direction quadrant. Our third analysis of the hourly 

ambient data confirms our general findings; however, the January 1, 2007 and January 

26, 2008 exceedance days may be exceptions and are discussed in Section 4.2, below. 

3.3.2 Review of 2010 and 2011 Exceedance Days

We did not use 2010 and 2011 data for our detailed meteorological analysis and 

attainment determination for two reasons. First, the 2010 dataset did not meet the 

completeness criteria specified in 40 CFR part 50, appendix K; no quarter in 2010 had 

complete data. This was due to a large data gap from March 16 to October 27 resulting 

from poor quality assurance and control results. Second, the 2011 dataset has yet to be 

entered completely into the Air Quality System database and certified by Arizona. As 

stated earlier, a complete year of air quality data, as defined by 40 CFR part 50, appendix 

K, comprises all four calendar quarters with each quarter containing data from at least 75 

percent of the scheduled sampling days. While the 2010 and 2011 ambient data do not 

provide the basis for this attainment determination, we examined this data consistent with 

the analyses presented in this document and found no information to contradict our 

conclusions.16

 

While we did not use the data from 2010 and 2011 for our detailed meteorological 

analyses, we did review this most recent data to see how ambient PM10 levels compare 

generally to our 2007 - 2009 dataset. In 2010, the Nogales, Arizona Post Office (Model: 

Met One BAM 1020) monitor recorded six exceedances of the twenty-four hour PM10

NAAQS; these twenty-four hour average ambient values ranged from 159 g/m3to 191 

g/m3. There was one exceedance of the PM10 standard in 2011. Arizona has not 

flagged any of these 2010 or 2011 exceedances for potential exclusion from air quality 

planning considerations under EPA’s Exceptional Events Rule. 

 

4.0 Findings 

From our three analyses, the Nogales NAA emissions inventory, the Nogales 

Municipality emissions inventory, and the 2007-2009 Meteorological Analysis, we find: 

The majority of exceedances, 79 percent, occur in the October to January 

timeframe, mostly in November.17 Also, given the high desert environment and 

 

16 See Section 4.5 in Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, 

Arizona: 2007 - 2009, in Appendix C.

17

 See Figure 3, Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, 

Arizona: 2007 - 2009, in Appendix C. 
23

winter light regime, temperatures usually drop dramatically, 20 degrees 

Fahrenheit over the 3-4 hours after sunset.18 

From the emission inventories, we estimate that pollution loads may differ by a 

ratio of 1.8 - 4.6 to one on a south-to-north basis in relation to the international 

border. 

The largest sources of PM10 emissions in the Ambos Nogales area are reintrained 

dust from unpaved and paved roads. 

Overall, elevations drop approximately 709 feet across the entire south to north 

local transect we examined, from the southernmost edge of the Nogales, Sonora 

urban boundary to the Nogales NAA northern boundary line. 

Of the 29 exceedance days in 2007 - 2009, 26 of those days 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 

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

On exceedance days, the largest proportions, 71-92 percent, of hourly values 

exceeding 150 g/m3and almost all of the highest observed PM10 concentrations 

of observations above 450 g/m3 , 92 percent, are associated with a southerly 

wind direction quadrant.19

The ambient PM10 concentration attributed to the southerly wind quadrant 

exceeds 150 g/m3

on all 29 exceedance days. In contrast, two exceedance days 

from the “all other wind direction” quadrants show a value greater than 150 

g/m3: January 1, 2007, and January 26, 2008. 

Only one of 29 exceedance days shows the concentration attributed to the “all 

other wind direction” quadrants greater than that of the concentration attributed to 

the southerly wind quadrant: January 1, 2007. 

On exceedance days, the average ratio of the southerly wind quadrant share of 24-

hour ambient PM10 values to all other wind quadrants share of ambient values is 

3.83 to 1. This ratio is relatively consistent with the estimated pollution loads 

ratio of 1.8 - 4.6 to one, from south-to-north across the international border. 

 

18

 See Figures 7 and 14, Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in 

Nogales, Arizona: 2007 - 2009, in Appendix C. 

19

 See Table 11 above. For a visual representation of this data, see the pollution roses in Figures 11 and 

12, Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007 - 

2009, in Appendix C. 
24

4.1 A Conceptual Model of 2007 - 2009 Exceedance Days 

As described above in Section 3.3, 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 exceptions were January 1, 

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

similar meteorological and concentration patterns throughout the rest of the day. Two of 

the 29 exceedance days, January 1, 2007, and January 26, 2008, had high average 

ambient concentrations during hours when the wind was out of directions other than the 

south. 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. 

Considering these 25 similar exceedance days, we can postulate how the elements of 

pollution loads and sources, temperature changes, and wind direction may contribute to 

producing the majority of observed ambient PM10 values exceeding the NAAQS in 

Nogales, Arizona. We will review the data concerning January 1, 2007, January 26, 

2008, May 22, 2008, and January 1, 2009 in more detail within Section 4.2. 

As shown for the average PM10 concentration, wind speed, and temperature profiles in 

Figure 3, beginning at midnight, there is a strong pattern of decreasing PM10

concentrations from the previous day’s high values into the early morning hours. Then, 

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

suggesting a reproducible direct PM10 source, such as reintrained road dust from the 

morning commute. As morning temperatures rise, so does wind speed as wind direction 

changes from south to north dispersing the spike in morning PM10 concentrations. The 

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. 

As sunset approaches and night falls, the diurnal cooling cycle begins. Ambient 

temperatures drop and lower elevation air masses no longer rise with convection causing 

wind speed to drop and wind direction to be variable. As temperatures continue to drop 

after sunset, wind speeds drop and cold air masses flow down from higher elevations 

causing wind direction to shift from a variable/northerly direction to a southerly 

direction. A pronounced spike in PM10 concentration is then observed beginning 

between 4:00 pm and 6:00 pm; roughly corresponding with the evening commute hours. 

Concentrations remain high for several hours into the evening and gradually begin to 

decrease as midnight approaches. The highest concentrations of PM10 occur in these 

evening hours when reintrained dust from unpaved and paved roads may be captured by 

cold air flows moving south to north from higher elevations. Also, home heating 
25

combustion may add a component to the evening PM10 load and be captured in the 

evening southerly air flows. 

Figure 3: Average hourly PM10 concentration, wind speed, and temperature at the 

Nogales, Arizona Post Office FEM monitor versus time of day for all exceedances, 

excluding January 1, 2007, May 22, 2008, and January 1, 2009. 20

This pattern of exceedances is usually 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 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. 

The conceptual model we present is consistent with the study by Arizona State 

University, “Atmospheric, Hydroclimatic, and Anthropogenic Causes of Fugitive Dust in 

the Nogales, Arizona-Nogales, Sonora Airshed.”21

 In this study – based on a regression 

analysis of 815 daily PM10 observations at Nogales, Arizona, and 457 daily PM10

 

20

 The diurnal pattern shown in Figure 3 applies to 25 very similar exceedance days and also includes 

January 26, 2008. Elements of this discussion, however, may not apply to January 26, 2008 because of the 

higher observed PM10 concentrations when winds were from the east southeast. See Section 4.2.3 for a 

more detailed discussion of the January 26, 2008 exceedance day.

21 Completed in 2002 by A.W. Ellis, the final report is available through The Southwest Center for 

Environmental Researcy and Policy at http://scerpfiles.org/cont_mgt/doc_files/A-02-2.pdf. 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

50

100

150

200

250

300

350

400

450

500

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Wind Speed (mph)

PM10 (ug/m3)

Time (hour)

Concentration

Wind Speed

Temperature

Temperature (Fahrenheit)

80

90

70

60

50

40

30

20

10
26

observations at Nogales, Sonora, and other information – the authors conclude that 

stagnant atmospheric conditions over a large scale (i.e., a stagnant synoptic atmosphere) 

is the most important factor in predicting high daily PM10 concentrations.22 

As shown in Table 12 above, for these similar 25 days the ambient concentration 

attributed to the southerly wind direction quadrant always exceeds the 150 g/m3level, in 

most cases markedly. Conversely, the ambient concentration attributed to the all other 

wind direction quadrants never exceeds the 150 g/m3level. Across all 25 days, the 

average of the hourly concentration values for the hours with a southerly wind direction 

ranges from 163 to 369 g/m3for each of the days, with an average value across the 25 

days of 264 g/m3

. In comparison, the average of the hourly concentration values for all 

other wind direction quadrants ranges from 38 to 148 g/m3

for each of the days, with an 

average value across the 25 days of 80 g/m3

. 

In sum, for 25 of the 29 exceedance days, we have a conceptual model that explains how 

exceedances of the PM10 NAAQS occur in Nogales NAA. Moreover, for all of these 25 

days, the origin and contribution of PM10 to exceedances of the standard at the Nogales, 

Arizona Post Office monitor has a very large southerly component. Given the wind 

direction, the proximity of the monitor to the border, and the comparison of the 

magnitude of emissions on either side of the border, the majority of the emissions that 

result in these exceedances most likely originate from the Nogales, Sonora side of the 

international border. 

4.2 Review of Exceedance Days That Diverge From the Conceptual Model 

The conceptual model of Mexican influence on Nogales NAA PM10 concentrations 

described above fits the observations on 25 of the 29 exceedance days in 2007-2009. We 

have identified, however, four specific exceedance days that differ in one or more ways 

from our conceptual model of PM10 exceedances in the Nogales NAA: January 1, 2007, 

May 22, 2008, January 26, 2008, and January 1, 2009. We will examine each of these 

days in further detail to explain the high ambient PM10 values that occurred on those 

days. 

 

22

 With respect to soil moisture, this study noted a weak relationship between hydroclimatological 

conditions and high PM10 concentrations, i.e., while the soil is driest during the hot summer months of June 

through August, high PM10 concentrations typically occur during late fall through early spring months. In 

considering soil moisture related predictors of daily PM10 concentrations, the study did observe that the 

rate of daily drying is associated with higher observed PM10 concentrations, and that episodes of high PM10

were generally marked by more than twice the length of time since the last precipitation event when 

compared to episodes of low concentration. Despite these associations that soil moisture plays a role in 

high PM10 concentrations, the study concluded the following: overall conditions in the Nogales area are 

conducive to generating PM10 emissions throughout the year; and, meteorological conditions most strongly 

distinguish between high and low PM10 concentrations on a given day. 
27

4.2.1 January 1, 2007 Exceedance Day Review 

Table 13: January 1, 2007 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant. 

Figure 4: January 1, 2007 PM10 concentrations and wind speeds compared to average 

PM10 concentrations and wind speeds from Figure 3.23

As shown in Figure 4, with higher early morning PM10 concentrations contributing more 

strongly to the high 24-hour average, the PM10 diurnal pattern for January 1, 2007 varies 

from the average diurnal pattern for the 26 exceedance days. The diurnal pattern after 

mid-day looks similar to our conceptual model exceedance day, with an increase in 

hourly PM10 concentrations at 6:00 pm; however, this increase is less pronounced than 

our conceptual model exceedance day and the 24-hour exceedance is driven by the high 

early morning peaks. An examination of the hourly PM10 values shows high PM10

observations, from variable and backing wind directions, and very low wind speeds 

during the midnight to 8:00 am timeframe. 

The average PM10:PM2.5 ratio of all 2007 - 2009 days with valid samples was 6.24 

(standard deviation equals 2.89). The ratio observed on January 1, 2007 is the lowest in 

 

23 As discussed in Section 4.1 and shown in Figure 3, the average PM10 concentrations and windspeeds 

depicted in Figures 4, 5, 6, and 7 exclude observations from January 1, 2007, May 22, 2008, and January 1, 

2009. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

12:00:00 

...

1:00:00 AM2:00:00 AM3:00:00 AM4:00:00 AM5:00:00 AM6:00:00 AM7:00:00 AM8:00:00 AM9:00:00 AM

10:00:00 

...

11:00:00 

...

12:00:00 

...

1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PM7:00:00 PM8:00:00 PM9:00:00 PM

10:00:00 

...

11:00:00 

...

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

Average PM10

SWS (mph)

Average SWS

24-hour PM10

Concentration (μg/m3)

Southerly Wind Quadrant PM10

Concentration (μg/m3)

(135 to 224 degrees)

All Other Wind Direction PM10

Concentration (μg/m3)

(225 to 134 degrees)

210 199 (15 of 24 values) 231 (9 of 24 values)
28

the 2007 - 2009 sample period (1.49), suggesting that the large early morning ambient 

PM10 values were caused by a combustion source such as residential wood burning.24

4.2.2 January 26, 2008 Exceedance Day Review 

Table 14: January 26, 2008 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant.

Figure 5: January 26, 2008 PM10 concentrations and wind speed compared average PM10

concentrations and windspeeds from Figure 3. 

As shown in Figure 5, the PM10 diurnal pattern for January 26, 2008 is nearly the same as 

the conceptual model day and the other 25 exceedance days (excluding January 1, 2007, 

May 22, 2008, and January 1, 2009 from the 29 exceedances), with high evening PM10

concentrations contributing most to the high 24-hour average. The diurnal pattern during 

mid-day looks the same as our conceptual model exceedance day, with decreasing hourly 

PM10 concentrations from 9:00 am as wind speeds increase. There is a slight morning 

PM10 spike beginning at 6:00 am, but that is dispersed by rising low winds, again 

consistent with our conceptual model day. An examination of the hourly PM10 values 

shows the highest PM10 observations occurring in the evening (7:00-8:00 pm) from an 

east southeast direction (ESE); just outside of our defined southerly quadrant of 135-224 

degrees. These two hourly values greater than 550 g/m3are the only two from the ESE 

direction across all observed values on exceedance days. For further comparison, less 

 

24 For the complete discussion of coarse versus fine particulate matter on all exceedance days, see Section 

4.4 and Table 8 of Analysis of Ambient PM10 Levels, Topography, and Meteorological Data in Nogales, 

Arizona: 2007 - 2009, in Appendix C. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

12:00:00 AM

1:00:00 AM2:00:00 AM3:00:00 AM4:00:00 AM5:00:00 AM6:00:00 AM7:00:00 AM8:00:00 AM9:00:00 AM

10:00:00 AM11:00:00 AM

12:00:00 PM

1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PM7:00:00 PM8:00:00 PM9:00:00 PM

10:00:00 PM11:00:00 PM

Wind Speed (mph)

PM10 Concentration (ug/m3)

PM10 (ug/m3)

Average PM10

SWS (mph)

Average SWS

24-hour Concentration

(μg/m3)

Southerly Wind Quadrant 

Concentration (μg/m3)

(135 to 224 degrees)

All Other Wind Direction 

Concentration (μg/m3)

(225 to 134 degrees)

204 257 (7 of 24 values) 182 (17 of 24 values)
29

than 2 percent of hourly wind observations were from the ESE wind direction on all days, 

including non-exceedance days. 

The average PM10:PM2.5 ratio of all 2007 - 2009 days with valid samples was 6.24 

(standard deviation equals 2.89). The ratio observed on January 26, 2008 is near the 

average for the entire period (5.7), suggesting that ambient PM10 values were caused by 

emission sources similar to those on other exceedance days. 

4.2.3 May 22, 2008 Exceedance Day Review 

Table 15: May 22, 2008 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant.

Figure 6: May 22, 2008 PM10 concentrations and wind speeds compared to average PM10

concentrations and wind speeds from Figure 3. 

Compared to the other twenty-eight exceedance days in our data set, May 22, 2008 is the 

only exceedance day associated with elevated windspeeds, some as high as 17 miles per 

hour (mph). See Figure 6. Also, the PM10 diurnal pattern for May 22, 2008 is not at all 

similar to the average of the 26 exceedance days as PM10 concentrations peak around 

4:00 pm consistent with the daily high wind speed for the day of 17 mph, and PM10 levels 

continue to fall with decreasing wind speed. An examination of the wind direction shows 

that all winds originated from the southerly wind quadrant (135-224 degrees). 

The average PM10:PM2.5 ratio of all 2007 - 2009 days with valid samples was 6.24 

(standard deviation equals 2.89). Consistent with the high wind speeds, the ratio 

observed on May 22, 2008 is the highest in the 2007 - 2009 sample period (10.96), 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

Average PM10

SWS (mph)

Average SWS

24-hour Concentration

(μg/m3)

Southerly Wind Quadrant 

Concentration (μg/m3)

(135 to 224 degrees)

All Other Wind Direction 

Concentration (μg/m3)

(225 to 134 degrees)

217 217 (24 of 24 values) No Observed Values
30

suggesting that the high late afternoon ambient PM10 values were caused by sources of 

coarse particulate matter and windblown dust, such as disturbed open areas and unpaved 

roads. 

4.2.4 January 1, 2009 Exceedance Day Review 

Table 16: January 1, 2009 PM10 Concentration: 24-hour value and hourly values 

disaggregated by southerly wind quadrant.

Figure 7: January 1, 2009 PM10 concentrations and wind speeds compared to average 

PM10 concentrations and wind speeds from Figure 3.

As shown above, with higher early morning PM10 concentrations contributing more 

strongly to the high 24-hour average, the PM10 diurnal pattern for January 1, 2009 varies 

from the average diurnal pattern for the 26 exceedance days. The diurnal pattern after 

mid-day looks similar to other days, with an increase in hourly PM10 concentrations at 

6:00 pm; though the increase is less pronounced than the average of other exceedance 

days. An examination of the hourly PM10 values shows the highest PM10 observations 

from the southerly wind quadrant from midnight to 4:00 am and in the evening, 8:00-

11:00 pm and very low wind speeds during these timeframes. 

The average PM10:PM2.5 ratio of all 2007 - 2009 days with valid samples was 6.24 

(standard deviation equals 2.89). The ratio observed on January 1, 2009 is the second 

lowest in the 2007 - 2009 sample period (1.67), suggesting that the large early morning 

ambient PM10 values were caused by a combustion source such as residential wood 

burning, similar to the January 1, 2007 exceedance day. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

Average PM10

SWS (mph)

Average SWS

24-hour Concentration

(μg/m3)

Southerly Wind Quadrant 

Concentration (μg/m3)

(135 to 224 degrees)

All Other Wind Direction 

Concentration (μg/m3)

(225 to 134 degrees)

238 323 (14 of 24 values) 119 (10 of 24 values)
31

4.3 Estimate of Expected Exceedance Days “But For” International Transport 

Consistent with the Attainment Guidance discussed in Section 2.3, the standard used to 

determine attainment of the PM10 NAAQS in the Nogales NAA, “but for” international 

emissions is as follows: the expected number of days per calendar year with a 24-hour 

average concentration above 150 μg/m3 must be equal to or less than one. So, to 

determine that the Nogales NAA has met the PM10 standard “but for” emissions from 

Mexico, our 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 within the Nogales NAA, and that all other monitored exceedances of 

the NAAQS originate from Mexico. 

We used two analyses to estimate the expected exceedance days in the Nogales NAA 

“but for” international transport. In the first analysis of exceedance days, we estimated 

the number of exceedances of the NAAQS that would have occurred but for international 

sources by identifying those exceedance days for which the available information and 

analyses suggest a significant influence from Mexican emission sources and counting the 

exceedance days that remain. In our second analysis of hourly concentrations, we 

classified each hour of the exceedance days based on the likely influence from Mexico 

and then recalculated a 24-hour average concentration that would have occurred but for 

international transport of PM10 emissions from Nogales, Sonora. Both analyses are 

presented below. 

4.3.1 Daily Analysis 

As discussed in Section 4.1, we have a conceptual model that explains how exceedances 

of the PM10 NAAQS occur in the Nogales NAA on 25 of the 29 exceedance days in 2007 

- 2009. From our day-by-day review above, we can decide, whether or not, to assign the 

four remaining exceedance days — 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. 

First, the May 22, 2008 exceedance day is wholly different from our conceptual model 

exceedance day given the relative high windspeeds and higher than usual coarse PM 

component likely from disturbed surfaces. As with total PM10 emissions, emissions of 

coarse PM (e.g., unpaved roads) are higher from Nogales, Sonora, than they are from the 

Nogales NAA. The wind direction is from a southerly quadrant in all hourly 

observations. Given this information, we find that the 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. 

Second, the January 1, 2009 exceedance day is different from our 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
32

emissions, emissions of fine PM (e.g., combustion sources) are higher from Nogales, 

Sonora, than they are from the Nogales NAA. 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. Consequently, 

we find that the 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, too, is different from our 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. 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 

twenty-four hour average concentration. Although more detailed and different field 

studies might prove otherwise, with the information available, our analysis is 

inconclusive as to whether this exceedance is attributable to a disproportionate 

international contribution and the Nogales NAA would not have exceeded the PM10

NAAQS but for emissions from Mexico. It is possible that the PM10 emissions originated 

south of the U.S.-Mexico border and were blown into the area, but then persisted during 

periods of calm and variable winds. 

Finally, our review of the January 26, 2008 exceedance day suggests that this day is most 

like our 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 g/m3

level. Again, 

while specifically designed field studies might help adjudicate the relative contributions 

to this exceedance, with the information available, our analysis is inconclusive as to 

whether this exceedance is attributable to a disproportionate international contribution 

and the Nogales NAA would not have exceeded the PM10 NAAQS but for emissions 

from Mexico. It is possible that the PM10 emissions originated south of the U.S.-Mexico 

border and were blown into the area, but then persisted during periods of calm and 

variable winds. 

To summarize, we find that two exceedance days, May 22, 2008 and January 1, 2009, 

should be categorized with the 25 exceedance days where we have found a high 

likelihood of a large contribution of PM10 from sources on the Nogales, Sonora side of 

the international border from the Nogales NAA. The two remaining exceedance days, 

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

Nogales NAA side of the international border such that we 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. 

Therefore, using this daily analysis, we find that at least 27 of 29 exceedances of the 

PM10 NAAQS observed in the Nogales NAA during 2007 - 2009 can be attributed to 

sources of PM10 from across the international border. Based on data completeness and 
33

every day sampling for the 2007 - 2009 timeframe, we calculated a maximum expected 

annual exceedance rate of 0.7 exceedances per year. 

4.3.2 Hourly Analysis 

In our second analysis, we classified each hourly PM10 concentration value from the 29 

exceedance days based on the likely influence of emissions from Mexico and then 

recalculated the 24-hour average concentration that would have occurred but for 

international transport of PM10 emissions from Nogales, Sonora. To begin, we classified 

each hour of the 29 exceedance days based on the likelihood of significant international 

transport. An hourly concentration was classified as influenced by international transport 

if it met one of four criteria or decision rules related to hourly observations of wind 

direction, wind speed, and temperature change: 

1) hours with sustained (more than one hour consecutively) southerly winds greater 

than 4.5 mph (2 meters/second (m/s)), suggesting the primary influence of windblown dust from across the international border; 

2) hours with southerly winds or air flow and decreasing or stable temperatures 

preceded by or followed by hours with similar conditions, suggesting sustained 

downslope air flows from higher elevations south of the international border; 

3) any hour preceded by and followed by hours with southerly wind or air flow and 

decreasing or stable temperatures, suggesting continued influence of downslope 

air flow from higher elevations south of the international border; and, 

4) surface wind speed less than or equal to 1.1 mph (0.5 m/s), preceded by or 

followed by hours with similar conditions, suggesting sustained air mass 

stagnation where PM10 emissions suspended in previous hours remain suspended 

in the stagnant air mass. 

The first criterion identifies periods consistent with sustained high winds from the south 

carrying wind-blown dust, as discussed in Section 4.2.3 concerning the May 22, 2008 

exceedance day. The second and third criteria identify periods influenced by downslope 

wind flow conditions described in the conceptual model as usually occurring in the late 

afternoon and evening. The fourth criterion identifies 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. 

The analysis of emissions inventories discussed in section 3.2 concluded that U.S. 

sources are responsible for a maximum of 36 percent of PM10 emissions in the Ambos 

Nogales region. Therefore, for each hour that meets one of the four criteria listed above, 

instead of assuming that the concentration is due entirely to Mexican sources, a more 

conservative assumption is that up to 36 percent of the hourly concentrations may be due 

to contributions from U.S. emission sources. Therefore, in this next step, we weighted 
34

the observed hourly concentrations by 0.36 for each hour that meets any one of the four 

criteria listed above and used this weighted concentration to estimate the 24-hour average 

concentration that would have occurred in the Nogales NAA but for international 

transport. 

 

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.25

 

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/m3and 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 sum, based on this analysis apportioning hourly concentration data using the four 

criteria to produce an estimated 24-hour average concentration but for international 

emissions, no exceedance days would have been expected to occur in the Nogales NAA, 

but for transport from Mexico. 

Considering the relatively large differences in emissions inventories between the Nogales 

NAA and Nogales, Sonora and the meteorology described by our conceptual model, it is 

likely that observed pollution during southerly downslope wind flows originating from 

Nogales, Sonora also contributed to observed pollution during following hours of 

sustained stagnation. With the wind direction varying under low wind speeds and stable 

temperatures, it remains possible, however, that a greater proportion of PM10 pollution 

during hours of sustained stagnation may be coming from U.S. sources. Therefore, a 

slightly more conservative approach would be to relax our criteria by not considering 

sustained stagnation (Rule 4) and assign PM10 levels during these hours entirely to the 

Nogales NAA. Consequently, when we consider Mexican influence to only occur under 

conditions of relative high wind speeds (Rule 1) and sustained downslope wind flows 

from the south (Rules 2 and 3), two exceedance days would have been expected to occur 

but for international transport: January 1, 2007 and January 26, 2008. Given the finding 

that no more than two exceedance days would have occurred applying criteria one 

 

25

 The observed concentrations and meteorological data for each hour of each exceedance day, the 

classification based on the criteria listed above, and the re-calculation of the estimated 24-hour average 

concentrations but for international transport are provided in Section 3.7 of Analysis of Ambient PM10

Levels, Topography, and Meteorological Data in Nogales, Arizona: 2007 - 2009 in Appendix C.
35

through three, as determined by this hourly analysis of concentration data, the maximum 

expected number of annual exceedances is 0.7. 

5.0 Conclusion 

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

expected number of days per calendar year with a 24- hour average concentration above 

150 μg/m3are less than or equal to one, based on data completeness and every day 

sampling. To determine that the Nogales NAA has met the PM10 standard “but for” 

emissions from Mexico, our analysis must show that no more than three exceedances of 

the standard in the 2007 - 2009 analysis period would have occurred in the absence of 

pollutant flows from Mexico. 

Using two different analyses to estimate the expected number of exceedance days, we 

have concluded that no more than two of the exceedance days in 2007 - 2009 would have 

occurred but for transport from Mexican sources. Given that the annual expected 

exceedance rate, 0.7, is less than or equal to one, we conclude that the Nogales NAA 

attains the PM10 NAAQS “but for” PM10 emissions originating from across the 

international border. 
This page is intentionally blank. 
36

Appendix A: 2008 and 2011 Emissions Inventory for Nogales NAA 

Appendix B: 2008 and 2011 Emissions Inventory for the Nogales 

Municipality, Sonora, Mexico 

Appendix C: Analysis of Ambient PM10 Levels, Topography, and 

Meteorological Data in Nogales, Arizona: 2007 – 2009 
1

PM10 Emissions 

Inventories for 

2008 and 2011

Nogales

Non-Attainment Area

Santa Cruz County, Arizona

U.S. Environmental Protection Agency

Region 9

Draft Final, July 20, 2012
This page is intentionally blank. 
2

Table of Contents 

1. Introduction................................................................................................3

2. The Nogales Nonattainment Area.......................................................................4 

3. Emissions Inventory Methodology......................................................................9 

4. 2008 Emissions Inventory and Discussion............................................................12 

5. 2011 Emissions Inventory Projection ..................................................................14

Appendix 1: MOVES 2008 output file and run specification 

Appendix 2: MOVES 2011 output file and run specification 
3

1. Introduction 

1.1 Purpose 

This document provides a PM10 emission inventory for all PM10 sources within the Nogales 

Nonattainment Area (NAA) and the details concerning the derivation of those emissions 

estimates. The Arizona Department of Environmental Quality (ADEQ) requested that EPA 

create this PM10 emissions inventory to support ADEQ’s work on a PM10 State Implementation 

Plan (SIP) for the Nogales NAA, located in Santa Cruz County, Arizona. 

1.2 Sources of PM10

PM10 refers to particulate matter of ten microns or less in aerodynamic diameter. Another class 

of particles, denoted as PM2.5, also called fine particulate, refers to particles of 2.5 microns or 

less in aerodynamic diameter. PM10 includes both PM2.5 and the particulates with aerodynamic 

diameter between 2.5 and 10 microns. Sometimes referred to as PM2.5-10, this larger fraction is 

called “coarse” particulate. While fine particles originate mostly from combustion sources and 

secondary aerosol generation processes, coarse particles usually originate from mechanical 

activities and fugitive source categories. Typical major sources of PM10 include fugitive dust, 

open burning including wild fires, mineral crushing and grinding operations, agricultural 

activities such as land tilling, dust suspended from vehicle travel on paved and unpaved roads 

and, to a lesser extent, fuel combustion sources and mobile source exhaust. 

1.3 Emissions Inventory Overview 

Most of the emissions data for this inventory came from version 1.5 of United States 

Environmental Protection Agency’s (EPA) 2008 National Emissions Inventory (NEI) for Santa 

Cruz County, Arizona; any use of other data is noted. EPA prepares the NEI every three years. 

The NEI is a comprehensive and detailed estimate of air emissions of both criteria and hazardous 

air pollutants from all air emissions sources and is based primarily on emission estimates and 

emission model inputs provided by state, local, and tribal air agencies for sources in their 

jurisdictions, and supplemented by data developed by the EPA. More information about the 

2008 NEI, including methodologies and assumptions used in producing this emissions inventory, 

may be found at the following URL: http://www.epa.gov/ttn/chief/net/2008inventory.html. 

The NEI allocates emissions at the county level. To develop an inventory for the nonattainment 

area from the NEI, the county-level emissions estimates must be allocated to the nonattainment 

area. The methods used for allocating county level emission estimates to the nonattainment area 

are described in Section 3 of this document. 
4

2. The Nogales Nonattainment Area 

 

2.1 Overview of the Area 

The southern boundary of the Nogales NAA and Santa Cruz County is the U.S./México border. 

At the lower center of the Nogales NAA, the city of Nogales, Arizona is sixty miles south of 

Tucson, Arizona in the middle and southernmost portion of Santa Cruz County. The city of 

Nogales, Arizona is the largest city in the nonattainment area. See Figure 1 below. 

Regarding topography, the Nogales NAA is located within the Sonoran Desert. This desert 

covers 120,000 square miles with a minimum elevation of 2,500 feet and is in the Basin and 

Range topographic province. This topography is characterized by north-south elongated valleys 

surrounded by mountain ranges. Nogales is located in such a north-south valley created by the 

Nogales Wash running north to the 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 25 

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. 

Major highways in the Nogales, Arizona area are Arizona State Route 82, which connects 

Nogales, Arizona with Patagonia, Arizona (19 miles) and Sonoita (31 miles) to the northeast, and 

U.S. Interstate 19 which connects Tucson, Arizona to Nogales, Arizona and continues south into 

México, where it becomes Federal Highway 15. 

Nogales, Sonora, Mexico lies directly south of Nogales, Arizona across the international border. 

Taken together and referred to as Ambos Nogales, the communities of Nogales, Arizona and 

Nogales, Sonora, México comprise the largest international border community in Arizona, with a 

combined population of 232,550 inhabitants in 2010.1 The mean elevation in Nogales, Sonora is 

4,265 feet above sea level.2 At 5,380 feet, the highest elevation area in Nogales, Sonora are in 

the Cerro de los Nogales (Nogales Hill), west of where the Obregón and Colosio routes meet, 

near the southern end of the city. 

The Alvaro Obregón Boulevard, Luis Donaldo Colosio Boulevard, and the Corredor Fiscal toll 

road are the main transportation routes in Nogales, Sonora. The Alvaro Obregón Boulevard runs 

the length of the narrow Nogales Wash valley, and is a highly congested route used by local and 

some cross-border commercial traffic. The Corredor Fiscal is a toll road for cross-border 

commercial traffic; its on- and off-ramp access is limited to the border junction at Mariposa 

Road and a point just outside of the southern city limits of Nogales, Sonora. The Corredor Fiscal 

conducts the majority of the U.S. and Mexico cross-border commercial traffic. 

 

1

 Nogales, Arizona had 20,017 inhabitants and Nogales, Sonora, Mexico had 212,533 inhabitants. U.S. 

Census Bureau 2010 and Instituto Nacional de Estadistica Geografia e Informatica, (INEGI) 2010.

2

 “Statistical Municipal Workbook for Nogales, Sonora,” 2005 edition, INEGI. 
5

Figure 1: Ambos Nogales and Nogales PM10 Nonattainment Area 

!(

Nogales,

Sonora

Nogales, Arizona

M E X I C O

U N I T E D S T A T E S

AMBOS NOGALES AND NOGALES ARIZONA

PM-10 NONATTAINMENT AREA

AIR1200002_1.mxd October 5, 2011

Sources: U.S. Census Bureau (2000),

ESRI (2011), TANA (2006),EPA (2011).

!( PM-10, PM-2.5 Monitoring Station

Nogales, Arizona Boundary

Nogales, Sonora Boundary

PM-10 Nonattainment Area

International Boundary

0 2.5 Ü5 10 Miles
6

2.2 Population and Urbanization 

This section presents the population estimates for Santa Cruz County and the Nogales NAA. 

There are two population centers in Santa Cruz County and the Nogales NAA: the City of 

Nogales; and, Rio Rico. Only a portion of Rio Rico, however, lies within the Nogales NAA 

boundaries. 

2.2.1 Santa Cruz County 

In 2010, the U.S. Census estimated the Santa Cruz County population to be 43,716; up 1.45 

percent from 43,091 in 2008.3 

2.2.2 The City of Nogales, Arizona 

In 2010, the U.S. Census estimated the population of Nogales to be 20,837; up 5.49 percent from 

19,752 in 2008.4 From 2000 to 2010, the population of Nogales decreased slightly, 0.2 percent; 

in comparison, the County population grew 13.9 percent.5 

2.2.3 Rio Rico Community 

Río Rico is an unincorporated community in Santa Cruz County located twelve miles north of 

the U.S./México border and 57 miles south of Tucson. The community resides on 39,000 acres 

in the foothills of the Santa Rita Mountains. Economic activities include light manufacturing, 

and produce staging and distribution in the industrial facilities of the Río Rico South Industrial 

Park. 

Because a portion of the Rio Rico community is within the Nogales NAA, we developed an 

estimate of this population using the U.S. Census and allocation percentages from the Arizona 

Commerce Authority (ACA). In the 2000 U.S. Census, Río Rico was listed as four Census 

Designated Places (CDPs): Rio Rico Northeast, Rio Rico Northwest, Rio Rico Southeast, and 

Rio Rico Southwest. Most of Rio Rico Southeast CDP and a portion of Rio Rico Southwest 

CDP are in the Nogales NAA. Using a Geographic Information System to estimate the Rio Rico 

land areas within the Nogales NAA, ADEQ determined that 88.7 percent of Rio Rico Southeast 

and 19.1 percent of Rio Rico Southwest are in the Nogales NAA; the two remaining two Rio 

Rico communities are outside of the boundaries of the nonattainment area. 

In 2010, the combined population of the four Rio Rico CDPs was estimated at 18,962

inhabitants, but the U.S. Census did not provide a separate population estimate for the four Rio 

Rico areas (U.S. Census 2010). Prior to the 2010 Census, the ACA provided a population 

estimate nearly equal to the 2010 Census figure and allocated this estimate across the four Rio 

Rico areas; we used the percentages derived from the 2010 ACA estimate to allocate the 2010 

 

3

 U.S. Census, www.census.gov/popest. 

4

 Ibid. 

5

 U.S. Census, www.census.gov/popest ; population figures: Nogales in 2000, 20,878; Nogales in 2010, 

20,837; Santa Cruz County in 2000, 38,381; Santa Cruz County in 2010, 43,716. 
7

U.S. Census figure to the four Rio Rico areas. We then scaled the four area estimates back from 

2010 to 2008 assuming the Rio Rico area grew consistent with the 2008 to 2010 Santa Cruz 

County U.S. Census estimates. Finally, using the land area allocations developed by ADEQ, we 

estimated population the 2008 contributions from Rio Rico Southeast and Rio Rico Southwest to 

the Nogales NAA population. Our calculations are shown below in Table 1. 

Table 1: 2008 Population Contribution from Rio Rico Communities to the Nogales NAA. 

Rio Rico CDP Area

2010 

Census

2010 ACA 

Estimates

2010 ACA 

Allocations 

2010 Census 

per ACA 

Allocation

2008 

Estimate 

Scaled per 

County* 

2008 Nogales 

NAA Contribution

Northeast - 4,921 26 percent 4,912 4,841 Area outside NAA 

Northwest - 5,408 28 percent 5,398 5,320 Area outside NAA 

Southeast - 3,439 18 percent 3,433 3,383 3,001

Southwest - 5,228 28 percent 5,219 5,143 982 

Totals 18,962 18,996 100 percent 18,962 18,687 3,983

* Santa Cruz County grew 1.45 percent from 2008 to 2010; figures are reduced accordingly. 

Source: U.S. Census, www.census.gov/popest 

2.3 Land-Areas of Santa Cruz County and the Nogales NAA 

Santa Cruz County comprises 1,237.6 square miles of land, or approximately 791,632 acres.6

The majority of land ownership in Santa Cruz County is distributed between the U.S. Forest 

Service (52.7 percent), private land-owners (37.6 percent), State of Arizona Trust Land (7.8 

percent), and the U.S. Bureau of Land Management (1.7 percent).7 See Figure 2 below. 

The Nogales NAA covers a land area of 76.1 square miles.8 In comparison with the County, the 

majority of the land in the nonattainment area is privately owned. The codified boundaries of the 

Nogales NAA can be found at 40 CFR Part 81.303. The Nogales PM10 nonattainment area is 

delineated by the following townships and ranges within the State of Arizona that lie east of 111 

degrees longitude: T23S, R13E; T23S, R14E; T24S, R13E; and, T24S, R14E. 

 

6

 U.S. Census, Santa Cruz County Quickfacts, http://quickfacts.census.gov/qfd/states/04/04023.html 

7

 Arizona State Land Department, Arizona Land Resource Information System (1994) 

8

 EPA Geographic Information System estimate. 
8

Figure 2: Santa Cruz County Land Ownership and Nogales PM10 Nonattainment Area.
9

3. Emissions Inventory Methodology 

3.1 EPA’s 2008 National Emissions Inventory 

This Nogales NAA emissions inventory is based on modifications to version 1.5 of EPA’s 2008 

National Emission Inventory (NEI). EPA's NEI database contains information about sources that 

emit criteria air pollutants and their precursors, and hazardous air pollutants. The database 

includes estimates of annual air pollutant emissions from point, nonpoint, and mobile sources in 

the fifty states, the District of Columbia, Puerto Rico, and the Virgin Islands available at the 

county level. Collaborating with the states, EPA develops the emissions inventory and releases 

an updated version of the NEI database every three years. 

Five of the six criteria air pollutants are included in the NEI database. Emissions of carbon 

monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), lead (Pb), and particulate matter 

(PM10 and PM2.5) are specifically reported in the NEI. Ozone, the sixth criteria air pollutant, 

arises from photochemical reactions in the atmosphere rather than direct emissions from sources. 

EPA compiled the NEI database from the primary data sources listed below: 

emissions inventories compiled by state and local environmental agencies; 

databases related to EPA's Maximum Achievable Control Technology (MACT) programs 

to reduce emissions of hazardous air pollutants; 

Toxic Release Inventory (TRI) data; 

for electric generating units, EPA's Emission Tracking System / Continuous Emissions 

Monitoring data (ETS/CEM) and Department of Energy fuel use data; 

for on-road sources, the Federal Highway Administration's estimate of vehicle miles 

traveled and emission factors from EPA's MOVES2030a computer model; 

for non-road sources, EPA's NONROAD2008a computer model; and, 

previous emissions inventories, if states do not submit current data. 

A complete description of the development of the 2008 NEI may be found at the following URL: 

http://www.epa.gov/ttn/chief/net/2008inventory.html.

3.2 On-Road Mobile Source Emissions 

In the 2008 NEI, on-road mobile source emissions were calculated using EPA’s MOBILE6 

model. Since the 2008 NEI was developed, EPA’s MOVES model has replaced MOBILE6 as 

the model for estimating emissions from cars, trucks, and motorcycles.9 On March 2, 2010, EPA 

approved the availability of the Motor Vehicle Emissions Simulator model (MOVES2010a) in 

official SIP submissions to EPA regarding air quality and for certain transportation conformity 

analyses outside the state of California.10

 MOVES2010a is the state-of-the-art upgrade to EPA’s 

modeling tools for estimating air emissions from cars, trucks, motorcycles, and buses, and is 

based on analyses of millions of emission test results and considerable advances in the Agency’s 

 

9

 http://www.epa.gov/otaq/models/moves/index.htm 

10 See 75 FR 9411 (March 2, 2010) 
10 

understanding of vehicle emissions. MOVES2010a was designed to replace the previous 

emissions model, MOBILE6.2, which was released in 2004. 

3.2.1 Calculating Santa Cruz County PM10 Emissions Using MOVES. 

EPA calculated the PM10 emissions from mobile sources in Santa Cruz County, Arizona using 

the MOVES2010a version dated September 23, 2010 (hereafter referred to as “MOVES”). This 

is the current version of the MOVES model. MOVES allows the use of county-specific data 

concerning factors such as the average speed distribution of on-road vehicles, daily vehicles 

miles traveled, and road types among others in place of national default values. The MOVES 

model requires the use of county specific data for SIP purposes. In this instance, the MOVES 

calculation was performed using input data from the 2008 NEI for Santa Cruz County. 

With the county-specific data in place, EPA prepared a run specification to identify the 

characteristics of a MOVES model run such as: scale, time span, vehicle and road type, and 

pollutants. The run specifications used for the 2008 and 2011 PM10 calculations can be found in 

Appendices 1 and 2. Based on the run specification, MOVES produces various summaries and 

output tables in MySQL format. The MySQL database can then be used to import the MOVES 

output into a variety of formats. In this instance, EPA staff used MySQL to produce the PM10

calculation in an Excel spreadsheet format; the resulting 2008 and 2011 output files are 

reproduced in tables within Appendices 1 and 2. 

3.3 Allocating the Santa Cruz County PM10 Emissions to the Nogales NAA 

EPA has no guidance on assigning emission sources from a county level of analysis to a smaller 

subject area within that county. For the Nogales NAA emissions inventory, EPA used a 

combination of population ratios, land area ratios, and source locations within the Nogales NAA 

to determine the appropriate allocation of county-wide emissions to the Nogales NAA. 

3.3.1 Emissions Scaling Based on Population 

One way to allocate emissions from a county-level to a smaller nonattainment area is to scale 

those emissions by a population ratio. In some cases, it is logical to scale source categories by 

population, since the rate of activities causing the emissions is more closely related to the 

number of people than to other factors, such as a specific land area relationship. 

As shown above, EPA used data from the U.S. Census Bureau was used to estimate the 2008 

population of the Nogales NAA population and Santa Cruz County. There are two assumptions 

underlying these calculations: first, we assume that the City of Nogales and the allocated 

population of Rio Rico comprise nearly all of the population within the nonattainment area. The 

remainder of the Nogales NAA is assumed to be rural and minimally populated. Second, as 

described in section 2.2.3, the individual 2008 Rio Rico area populations were allocated using 

2010 estimates from ACA and scaled back to 2008 according to the U.S. Census derived 

County-wide 2008 to 2010 growth rate. 
11 

When allocating emissions based on population, the county-level emissions for a given source 

category were multiplied by a factor of 55.1 percent to give the respective source category 

emissions for the Nogales NAA. See Table 2 below. If the likely magnitude of source category 

emissions varied with the activities of the population, it was allocated based on this population 

ratio. 

Table 2: Summary of Santa Cruz County and Nogales NAA Population Data 

Census Area 2008

2008 Percent 

of County 2010

2010 Percent 

of County

Santa Cruz County 43,091 43,716

City of Nogales 19,752 45.8 % 20,837 47.7%

Rio Rico (allocated value from Table 1) 3,983 9.2% 4,042 9.2%

Nogales NAA totals 23,735 55.1% 24,059 56.9%

Source: 2010 U.S. Census and www.census.gov/popest

The population estimates for Nogales are from the following U.S. Census Bureau population 

source: http://www.census.gov/popest . 

3.3.2 Emissions Scaling Based on Land Area 

A land area weighted emission ratio was developed using U.S. Census geographic data and/or 

Arizona Commerce Authority data.11 The land area for Santa Cruz County is 1,237.6 square 

miles. The land area for the Nogales NAA is 76.1 square miles. The ratio of Nogales NAA land 

area to the Santa Cruz County land area is calculated by dividing 76.1 by 1,237.6, which equals 

.061489 or 6.15 percent. 

For a spatial allocation of county-level emissions to the nonattainment area based on weighting 

by land area, the county-level emissions were multiplied by 6.15 percent to give the emissions 

for the Nogales NAA. Some source categories, such as agricultural emissions, are likely to be 

proportional to land area; consequently, they are logically allocated by the land area ratio. 

3.3.3 Source Emissions Identification Within the Nogales NAA.

To confirm whether specific sources in the Santa Cruz County emissions inventory should be 

included in the Nogales NAA inventory, EPA used visual inspections with location information, 

such as satellite photography using Google Earth. Also, EPA consulted with ADEQ. 

3.4 Summary of Land Area and Population Allocation Ratios 

Table 3: Summary of Land Area and 2008 Population Allocation Ratios.

Santa Cruz County Nogales NAA Allocation Ratio

Area (square miles) 1,237.612 76.1 6.15 percent

2008 Population 43,09113 23,73514 55.1 percent

 

11

 Arizona Department of Commerce Profile: Santa Cruz County Arizona, May 10, 2011, 

http://www.azcommerce.com/doclib/commune/Santa Cruzpercent20county.pdf. 

12 U.S. Census, Quickfacts, Santa Cruz County, Arizona. 

13 2010 U.S. Census population estimates. 
12 

4. 2008 Emissions Inventory and Discussion 

The Santa Cruz County emissions inventory and Nogales NAA allocation results are shown in 

Table 4. We discuss specific issues concerning the allocated emissions inventory in the sections 

following Table 4. 

Table 4: Santa Cruz County and Nogales NAA 2008 PM-10 Emissions Inventories (tons). 

Emissions Source Category

Santa Cruz 

County

Nogales 

NAA

Allocation 

Method

Agriculture - Crops and Livestock Dust 70.47 4.33 Area

Commercial Cooking - Charbroiling 11.36 6.26 Pop

Commercial Cooking - Frying 2.82 1.55 Pop

Dust - Paved Road Dust 220.39 121.43 Pop

Dust - Unpaved Road Dust 1,569.74 864.93 Pop

Dust - Road Construction 484.52 266.97 Pop

Dust - Commercial/Industrial/Institutional Construction 258.75 142.57 Pop

Dust - Residential Construction 43.45 23.94 Pop

Fires - Prescribed Fires 54.93 3.38 Area

Fuel Combustion - Electric Generation - Natural Gas 1.05 1.05 Loc

Fuel Combustion - Electric Generation - Oil 0.04 0.02 Pop

Fuel Combustion - Industrial Boilers, ICEs - Natural Gas 0.25 0.14 Pop

Fuel Combustion - Industrial Boilers, ICEs - Oil 1.04 0.57 Pop

Fuel Combustion - Industrial Boilers, ICEs - Coal --- --- See Section 4.1

Fuel Combustion - Residential - Wood 43.55 23.99 Pop

Fuel Combustion - Residential - Natural Gas, Oil, Other 1.51 0.83 Pop

Fuel Combustion - Commercial/Institutional - Oil 0.29 0.16 Pop

Fuel Combustion - Commercial/Institutional - Natural Gas 0.72 0.40 Pop

Fuel Combustion - Commercial/Institutional - Coal 0.04 0.02 Pop

Fuel Combustion - Commercial/Institutional - Other 0.02 0.01 Pop

Industrial Processes - Mining --- --- See Section 4.1

Mobile - Gasoline Vehicle - Off net roadways 1.22 0.67 Pop

Mobile - Gasoline Vehicle - Rural restricted access roads 1.76 0.97 Pop

Mobile - Gasoline Vehicle - Rural unrestricted access roads 2.59 1.43 Pop

Mobile - Gasoline Vehicle - Urban restricted access 1.33 0.73 Pop

Mobile - Gasoline Vehicle - Urban unrestricted access 8.37 4.61 Pop

Mobile - Diesel Vehicle - Off network roadways 1.1 0.61 Pop

Mobile - Diesel Vehicle - Rural restricted access roads 13.16 7.25 Pop

Mobile - Diesel Vehicle - Rural unrestricted access roads 5.51 3.04 Pop

Mobile - Diesel Vehicle - Urban restricted access 3.24 1.79 Pop

Mobile - Diesel Vehicle - Urban unrestricted access 12.15 6.69 Pop

Mobile - Non-Road Equipment - Diesel 15.48 8.53 Pop

 

14 Ibid. 
13 

Mobile - Non-Road Equipment - Gasoline 5.66 3.12 Pop

Mobile - Non-Road Equipment - Other 0.13 0.07 Pop

Mobile - Locomotives 1.70 0.63 Loc

Mobile - Aircraft 2.31 2.31 Loc

Waste Disposal - Residential Garbage Burning 41.77 23.02 Pop

Waste Disposal - Open Burning for Land Clearing 24.23 1.49 Area

Waste Disposal - Residential Yard Waste Burning 1.21 0.67 Pop

Waste Disposal - Institutional Incineration 0.28 0.28 Loc

Miscellaneous Non-Industrial NEC 0.44 0.24 Pop

TOTALS 2,908.58 1,530.7

Allocation method: Area = Land area ratio; Loc = Location; Pop = Population ratio.

4.1 Sources with Reported Locations 

There are inventory source categories that include sources with known locations. Since the 

location and emission rates for these sources are known, it is possible to determine if the sources 

are inside or outside the nonattainment area using mapping software. These source categories are 

discussed below. 

Fuel Combustion - Electric Generation - Natural Gas. A power plant, Valencia Power, is 

located within the nonattainment area. 

Fuel Combustion - Industrial Boilers, ICEs – Coal, 11.68 tons per year. Upon consulting 

with ADEQ about the source of these emissions entry, we were informed that this 

county-wide entry was an error and ADEQ will work with EPA to correct the 2008 NEI 

data. Consequently, these emissions were not included in the non-attainment area 

estimates. 

Industrial Processes – Mining, 761.11 tons per year. Upon consulting with ADEQ about 

the source of these emissions, we were informed that this county-wide entry was an error 

and ADEQ will work with EPA to correct the 2008 NEI data. Consequently, these 

emissions were not included in the non-attainment area estimates. 

Mobile – Aircraft. The only airport in the County, Nogales International Airport, is 

within the nonattainment area. 

Mobile – Locomotives. An estimated 11.0 of 29.8 miles of County rail track are within 

the nonattainment area; consequently, county-wide locomotive emissions were allocated 

by a 0.369 ratio. 

Waste Disposal - Institutional Incineration. A medical waste incinerator is located within 

the nonattainment area. 

4.2. Assessment of Emissions Estimates 

The 2008 estimated rate of PM10 emissions from road and other construction may be high 

because the emissions estimate does not reflect the full magnitude of the downturn in the real 

estate sector of the economy. It is likely that this downturn is a temporary situation and it may 

be expected that these emissions would resume at a higher level than once the real estate 
14 

economy improves. As a result, this emission rate is conservative and is based on the best 

estimates of construction activity available at this time. 

Also, the EPA could not identify locations of agricultural activities, prescribed forest burning, 

raising a source of uncertainty. While it is appropriate to apply a land ratio method for assigning 

County-level agricultural emissions to the nonattainment area, this may underestimate emissions 

given that intensive agricultural activity is likely to occur on private land, located primarily in the 

nonattainment area, as opposed to the public lands composing a large proportion of the 

remaining County. 

4.3 Overall Assessment 

The NEI provides a complete, timely and sufficiently accurate inventory for Santa Cruz County 

based on the best methodology and source data available at the time the inventory was 

developed. In allocating these County-wide emissions to the Nogales NAA, EPA has used 

reasonable and conservative assumptions to produce a current, accurate, and comprehensive 

nonattainment area PM10 emissions inventory. 

5. 2011 Emissions Inventory Projection

5.1 Overview 

Because 2008 is the year of the most current and complete national emissions inventory, we 

chose it as the base year for the emissions inventory and the Nogales PM10 attainment plan. 

Unfortunately, the Nogales NAA did not meet the PM10 NAAQS in 2008. It becomes important 

that the attainment plan characterize future emissions levels as part determining whether or 

where future controls may be needed to meet the PM10 NAAQS. Consequently, we have 

provided an emissions inventory for the year 2011. 

5.2 Methodology for Projecting the 2011 Emissions Inventory

PM10 emissions may rise or fall based on changes in three factors: economic conditions, 

population, and vehicle miles traveled (VMT). The accepted method for projecting emissions 

from base year inventories is to account for changes in these three factors as they may apply on a 

source sector basis. Below, we review each of these factors and their application to our 2008 

base year inventory. 

Considering economic conditions, there is an ongoing economic contraction in Arizona that 

began in 2007 and is projected to continue through 2011. Non-farm employment is projected to 

continue dropping through 2010 and 2011 according to the Economic and Business Research 

Center at the University of Arizona.15

 

15 http://ebr.eller.arizona.edu/dataentry/forecast.aspx. 
15 

The U.S. Census has calculated moderate population growth overall in Santa Cruz County, from 

43,091 in 2008 to 43,716 in 2010.16 Extrapolating this trend yields an estimated population 

increase of about 2.18 percent for the County from 2008 to 2011. The Nogales NAA appears to 

have grown faster than the County from 2008 to 2010, at 4.82 percent; so, its estimated increase 

from 2008 to 2011 is higher at 7.23 percent. While it may look like the Nogales NAA is 

growing precipitously, recall that the City of Nogales’s population decreased 0.2 percent 

between 2000 and 2010. A review of 2000-2010 City of Nogales population estimates shows 

slightly falling estimates after 2002, a large decrease in 2007, the lowest population estimate 

occurring in 2008, and a subsequent rebound through 2010. Given that we are only forecasting 

one year beyond 2010 census figures and most 2008-2011 population growth as already 

occurred, we are using the 7.23 percent growth factor to reflect actual population estimates for 

the 2008-11 period. 

Regarding VMT, the Federal Highway Administration's Highway Statistics17 series data on 

Arizona shows a decline in VMT between 2007 and 2008 and no change in VMT between 2008 

and 2009. This is consistent with economic conditions. Given a continuing or slowing economic 

contraction, there doesn't appear to be a reason to assume that VMT will increase within Santa 

Cruz County. EPA estimates for 2011 show a slight decrease in VMT. 

In summary, for our projection methodology and the 2011 emission inventory, we will assume 

the following: 

source categories tied to economic activity will not grow between 2008 and 2011; 

source categories that track with population growth will be estimated at the same rate as 

the Nogales NAA population growth, as opposed to the County growth rate, to reflect 

reported population change and to be conservative in estimating emissions; and, 

on-road mobile source will be estimated as discussed below. 

PM10 emissions from on-road mobile sources fall into four categories: brake and tire wear, 

vehicle exhaust, paved road dust, and unpaved road dust. As old on-road vehicles are replaced 

with newer, cleaner vehicles, exhaust emissions are expected to go down. Also, changes to 

cleaner fuel specifications lead to lower exhaust emissions. The overall changes in vehicle 

exhaust emissions are captured in the EPA MOVES emission model. MOVES also produces 

emissions estimates for brake and tire wear. EPA ran the MOVES model for 2011 to produce 

County-wide estimates for exhaust, brake, and tire-wear. Then, EPA scaled these emissions by 

the non-attainment area population ratio to estimate the 2011 emissions for these source 

categories. To be conservative and to reflect 2010 Census figures, we used a 0.569 ratio instead 

of the 0.551 ratio used for 2008 population based allocations. 

Other on-road PM10 emissions, such as paved and unpaved road emissions, do not vary with 

changes in the age of the vehicle fleet or changes in fuel. These emissions are affected primarily 

by VMT and local factors, such as dust loading on paved roads. This projection has estimated 

conservatively that these emissions will be constant from 2008 to 2011, despite a small 

anticipated decrease in VMT. 

 

16 http://www.census.gov/popest/eval-estimates/eval-est2010.html. 

17 http://www.fhwa.dot.gov/policyinformation/statistics.cfm. 
16 

5.3 2011 Emissions Inventory 

The 2011 emissions inventory results are shown in the table below. 

Table 5: Nogales NAA PM10 Emissions Inventories for 2008 and 2011 (tons per year). 

Emissions Source Category 2008 2011

Projection 

Method

Agriculture - Crops and Livestock Dust 4.33 4.33 No growth

Commercial Cooking - Charbroiling 6.26 6.71 Population

Commercial Cooking - Frying 1.55 1.67 Population

Dust - Paved Road Dust 121.43 121.43 No growth

Dust - Unpaved Road Dust 864.93 864.93 No growth

Dust - Road Construction 266.97 266.97 No growth

Dust - Commercial/Industrial/Institutional Construction 142.57 142.57 No growth

Dust - Residential Construction 23.94 23.94 No growth

Fires - Prescribed Fires 3.38 3.38 No growth

Fuel Comb - Electric Generation - Natural Gas 1.05 1.05 No growth

Fuel Comb - Electric Generation - Oil 0.02 0.02 No growth

Fuel Comb - Industrial Boilers, ICEs - Natural Gas 0.14 0.14 No growth

Fuel Comb - Industrial Boilers, ICEs - Oil 0.57 0.57 No growth

Fuel Comb - Residential - Wood 23.99 25.73 Population

Fuel Comb - Residential - Natural Gas, Oil, Other 0.83 0.89 Population

Fuel Comb - Commercial/Institutional - Oil 0.16 0.16 No growth

Fuel Comb - Commercial/Institutional - Natural Gas 0.40 0.40 No growth

Fuel Comb - Commercial/Institutional - Coal 0.02 0.02 No growth

Fuel Comb – Commercial/Institutional - Other 0.01 0.01 No growth

Mobile - Gasoline Vehicle - Off net roadway 0.67 0.56 MOVES

Mobile - Gasoline Vehicle - Rural restricted access roads 0.97 0.84 MOVES

Mobile - Gasoline Vehicle - Rural unrestricted access roads 1.43 1.33 MOVES

Mobile - Gasoline Vehicle - Urban restricted access 0.73 0.67 MOVES

Mobile - Gasoline Vehicle - Urban unrestricted access 4.61 4.47 MOVES

Mobile - Diesel Vehicle - Off network roads 0.61 0.40 MOVES

Mobile - Diesel Vehicle - Rural restricted access roads 7.25 4.73 MOVES

Mobile - Diesel Vehicle - Rural unrestricted access roads 3.04 2.09 MOVES

Mobile - Diesel Vehicle - Urban restricted access 1.79 1.22 MOVES

Mobile - Diesel Vehicle - Urban unrestricted access 6.69 4.72 MOVES

Mobile - Non-Road Equipment - Diesel 8.53 8.53 No growth
17 

Mobile - Non-Road Equipment - Gasoline 3.12 3.12 No growth

Mobile - Non-Road Equipment - Other 0.07 0.07 No growth

Mobile - Locomotives 0.63 0.63 No growth

Mobile - Aircraft 2.31 2.31 No growth

Waste Disposal - Residential Garbage Burning 23.02 24.68 Population

Waste Disposal - Open Burning for Land Clearing 1.49 1.60 Population

Waste Disposal - Residential Yard Waste Burning 0.67 0.71 Population

Waste Disposal - Institutional Incineration 0.28 0.30 Population

Miscellaneous Non-Industrial NEC 0.24 0.26 Population

TOTALS 1,530.7 1,528.16

5.4 Assessment of 2011 Inventory 

Population growth is relatively small, keeping those increases in emissions to a minimum. The 

lack of economic growth also retards emissions inventory growth. There is a notable drop in onroad emissions due to fleet turnover and new fuel standards. There is, however, little overall 

change between the 2008 and 2011 emissions inventories. 
18 

Appendix 1: MOVES 2008 Output File and Run Specification 

Output File: Definitions and Values 

Category 

Field Value Description

State ID 4 ARIZONA

County ID 4023 Santa Cruz County

Fuel Type ID 1 Gasoline

Fuel Type ID 2 Diesel Fuel

Road Type ID 1 Off-Network

Road Type ID 2 Rural Restricted Access

Road Type ID 3 Rural Unrestricted Access

Road Type ID 4 Urban Restricted Access

Road Type ID 5 Urban Unrestricted Access

Output File: PM-10 Total and Break Out by Fuel and Roadway Type (units in pounds) 

Fuel Road Run

Total 

PM10

Brake 

PM10

Elemental 

Carbon 

PM10

Organic 

Carbon 

PM10

Sulfate

PM10

Tire 

PM10

1 1 1 2440 0 814 1627 0 0

1 2 1 2465 293 306 2159 0 757

1 3 1 1774 2171 218 1556 0 1228

1 4 1 1194 959 152 1042 0 500

1 5 1 3445 10449 437 3008 0 2848

2 1 1 2202 0 605 1597 0 0

2 2 1 25301 439 22555 2746 0 576

2 3 1 10053 681 7867 2187 0 281

2 4 1 5795 542 4565 1230 0 146

2 5 1 20558 3232 15062 5496 0 504

Totals 75227 18766 52581 22648 0 6840
19 

Output File: Energy and Distance by Fuel and Roadway Type (units in MMBtu and miles) 

Fuel Road Run

Total 

Energy Distance

1 1 1 85644

1 2 1 482862 91817600

1 3 1 530307 103452000

1 4 1 238446 44182600

1 5 1 1135807 183604000

2 1 1 31765

2 2 1 494200 22257900

2 3 1 161149 9007850

2 4 1 93611 4440350

2 5 1 275949 12298100

Totals 3529740 471060400

MOVES 2008 Run Specification 

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21 

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22 

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useParameters No

]]></internalcontrolstrategy> 

 </internalcontrolstrategies> 

 <inputdatabase servername="" databasename="" description=""/> 

 <uncertaintyparameters uncertaintymodeenabled="false" numberofrunspersimulation="0" 

numberofsimulations="0"/> 

 <geographicoutputdetail description="COUNTY"/> 

 <outputemissionsbreakdownselection> 

 <modelyear selected="false"/> 

 <fueltype selected="true"/> 

 <emissionprocess selected="false"/> 

 <onroadoffroad selected="true"/> 

 <roadtype selected="true"/> 

 <sourceusetype selected="false"/> 

 <movesvehicletype selected="false"/> 

 <onroadscc selected="false"/> 

 <offroadscc selected="false"/> 

 <estimateuncertainty selected="false" numberOfIterations="2" keepSampledData="false" 

keepIterations="false"/> 

 <sector selected="false"/> 

 <engtechid selected="false"/> 

 <hpclass selected="false"/> 

 </outputemissionsbreakdownselection> 

 <outputdatabase servername="" databasename="2008SantaCruzOP42911" description=""/> 

 <outputtimestep value="Year"/> 

 <outputvmtdata value="false"/> 

 <outputsho value="false"/> 

 <outputsh value="false"/> 

 <outputshp value="false"/> 

 <outputshidling value="false"/> 

 <outputstarts value="false"/> 

 <outputpopulation value="false"/> 

 <scaleinputdatabase servername="" databasename="c04023y2008_in20110329" description=""/> 

 <pmsize value="0"/> 
23 

 <outputfactors> 

 <timefactors selected="true" units="Years"/> 

 <distancefactors selected="true" units="Miles"/> 

 <massfactors selected="true" units="U.S. Ton" energyunits="Million BTU"/> 

 </outputfactors> 

 <savedata> 

 </savedata> 

 <donotexecute> 

 </donotexecute> 

 <generatordatabase shouldsave="false" servername="" databasename="" description=""/> 

 <donotperformfinalaggregation selected="false"/> 

 <lookuptableflags scenarioid="" truncateoutput="true" truncateactivity="true"/> 

</runspec> 
24 

Appendix 2: MOVES 2011 Output File and Run Specification 

Output File: Definitions and Values 

Category 

Field Value Description

State ID 4 ARIZONA

County ID 4023 Santa Cruz County

Fuel Type ID 1 Gasoline

Fuel Type ID 2 Diesel Fuel

Road Type ID 1 Off-Network

Road Type ID 2 Rural Restricted Access

Road Type ID 3 Rural Unrestricted Access

Road Type ID 4 Urban Restricted Access

Road Type ID 5 Urban Unrestricted Access

Output File: PM-10 Total and Break Out by Fuel and Roadway Type (units in pounds) 

Fuel Road Run

Total 

PM10

Brake 

PM10

Elemental 

Carbon 

PM10

Organic 

Carbon 

PM10

Sulfate 

PM10

Tire 

PM10

1 1 1 1983 0 661 1321 0 0

1 2 1 1926 283 238 1688 0 734

1 3 1 1396 2104 172 1224 0 1191

1 4 1 941 930 119 822 0 485

1 5 1 2819 10137 359 2461 0 2764

2 1 1 1392 0 369 1022 0 0

2 2 1 15638 428 13642 1996 0 561

2 3 1 6394 665 4889 1505 0 274

2 4 1 3632 528 2794 838 0 142

2 5 1 12960 3149 9258 3702 0 492

Totals 49081 18224 32501 16579 0 6643
25 

Output File: Energy and Distance by Fuel and Roadway Type (units in MMBtu and miles) 

Fuel Road Run Total Energy Distance

1 1 1 83,885

1 2 1 463,338 89,093,696

1 3 1 508,149 100,401,000

1 4 1 228,870 42,884,000

1 5 1 1,088,672 178,216,000

2 1 1 30,836

2 2 1 481,052 21,702,200

2 3 1 157,447 8,825,700

2 4 1 91,302 4,341,050

2 5 1 269,850 12,053,900

Totals 3,403,401 457,517,546

MOVES 2011 Run Specification 

<runspec> 

 <description><![CDATA[2011 Santa Cruz County AZ test]]></description> 

 <modelscale value="Inv"/> 

 <modeldomain value="SINGLE"/> 

 <geographicselections> 

 <geographicselection type="COUNTY" key="4023" description="ARIZONA - Santa Cruz 

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 </geographicselections> 

 <timespan> 

 <year key="2011"/> 

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 <month id="2"/> 

 <month id="3"/> 

 <month id="4"/> 

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 <month id="7"/> 

 <month id="8"/> 

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 <month id="10"/> 

 <month id="11"/> 

 <month id="12"/> 

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sourcetypename="Combination Long-haul Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="61" 

sourcetypename="Combination Short-haul Truck"/> 
26 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="41" 

sourcetypename="Intercity Bus"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="32" 

sourcetypename="Light Commercial Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="54" 

sourcetypename="Motor Home"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="11" 

sourcetypename="Motorcycle"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="21" 

sourcetypename="Passenger Car"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="31" 

sourcetypename="Passenger Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="51" 

sourcetypename="Refuse Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="43" 

sourcetypename="School Bus"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="53" 

sourcetypename="Single Unit Long-haul Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="52" 

sourcetypename="Single Unit Short-haul Truck"/> 

 <onroadvehicleselection fueltypeid="2" fueltypedesc="Diesel Fuel" sourcetypeid="42" 

sourcetypename="Transit Bus"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="62" 

sourcetypename="Combination Long-haul Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="61" 

sourcetypename="Combination Short-haul Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="41" 

sourcetypename="Intercity Bus"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="32" 

sourcetypename="Light Commercial Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="54" 

sourcetypename="Motor Home"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="11" 

sourcetypename="Motorcycle"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="21" 

sourcetypename="Passenger Car"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="31" 

sourcetypename="Passenger Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="51" 

sourcetypename="Refuse Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="43" 

sourcetypename="School Bus"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="53" 

sourcetypename="Single Unit Long-haul Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="52" 

sourcetypename="Single Unit Short-haul Truck"/> 

 <onroadvehicleselection fueltypeid="1" fueltypedesc="Gasoline" sourcetypeid="42" 

sourcetypename="Transit Bus"/> 

 </onroadvehicleselections> 

 <offroadvehicleselections> 

 </offroadvehicleselections> 

 <offroadvehiclesccs> 

 </offroadvehiclesccs> 

 <roadtypes> 

 <roadtype roadtypeid="1" roadtypename="Off-Network"/> 

 <roadtype roadtypeid="2" roadtypename="Rural Restricted Access"/> 
27 

 <roadtype roadtypeid="3" roadtypename="Rural Unrestricted Access"/> 

 <roadtype roadtypeid="4" roadtypename="Urban Restricted Access"/> 

 <roadtype roadtypeid="5" roadtypename="Urban Unrestricted Access"/> 

 </roadtypes> 

 <pollutantprocessassociations> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="100" pollutantname="Primary Exhaust PM10 - 

Total" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="110" pollutantname="Primary Exhaust PM2.5 - 

Total" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="106" pollutantname="Primary PM10 - Brakewear 

Particulate" processkey="9" processname="Brakewear"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="102" pollutantname="Primary PM10 - Elemental 

Carbon" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="101" pollutantname="Primary PM10 - Organic 

Carbon" processkey="90" processname="Extended Idle Exhaust"/> 
28 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="105" pollutantname="Primary PM10 - Sulfate 

Particulate" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="107" pollutantname="Primary PM10 - Tirewear 

Particulate" processkey="10" processname="Tirewear"/> 

 <pollutantprocessassociation pollutantkey="116" pollutantname="Primary PM2.5 - Brakewear 

Particulate" processkey="9" processname="Brakewear"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="112" pollutantname="Primary PM2.5 - Elemental 

Carbon" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="111" pollutantname="Primary PM2.5 - Organic 

Carbon" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="1" processname="Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="15" processname="Crankcase Running Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="16" processname="Crankcase Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="17" processname="Crankcase Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="115" pollutantname="Primary PM2.5 - Sulfate 

Particulate" processkey="90" processname="Extended Idle Exhaust"/> 

 <pollutantprocessassociation pollutantkey="117" pollutantname="Primary PM2.5 - Tirewear 

Particulate" processkey="10" processname="Tirewear"/> 

 <pollutantprocessassociation pollutantkey="91" pollutantname="Total Energy Consumption" 

processkey="1" processname="Running Exhaust"/> 
29 

 <pollutantprocessassociation pollutantkey="91" pollutantname="Total Energy Consumption" 

processkey="2" processname="Start Exhaust"/> 

 <pollutantprocessassociation pollutantkey="91" pollutantname="Total Energy Consumption" 

processkey="90" processname="Extended Idle Exhaust"/> 

 </pollutantprocessassociations> 

 <databaseselections> 

 <databaseselection servername="" databasename="c04023y2008_in20110329" description=""/> 

 </databaseselections> 

 <internalcontrolstrategies> 

<internalcontrolstrategy 

classname="gov.epa.otaq.moves.master.implementation.ghg.internalcontrolstrategies.rateofprogress.RateOfProgress

Strategy"><![CDATA[ 

useParameters No

]]></internalcontrolstrategy> 

 </internalcontrolstrategies> 

 <inputdatabase servername="" databasename="" description=""/> 

 <uncertaintyparameters uncertaintymodeenabled="false" numberofrunspersimulation="0" 

numberofsimulations="0"/> 

 <geographicoutputdetail description="COUNTY"/> 

 <outputemissionsbreakdownselection> 

 <modelyear selected="false"/> 

 <fueltype selected="true"/> 

 <emissionprocess selected="false"/> 

 <onroadoffroad selected="true"/> 

 <roadtype selected="true"/> 

 <sourceusetype selected="false"/> 

 <movesvehicletype selected="false"/> 

 <onroadscc selected="false"/> 

 <offroadscc selected="false"/> 

 <estimateuncertainty selected="false" numberOfIterations="2" keepSampledData="false" 

keepIterations="false"/> 

 <sector selected="false"/> 

 <engtechid selected="false"/> 

 <hpclass selected="false"/> 

 </outputemissionsbreakdownselection> 

 <outputdatabase servername="" databasename="2008santacruzop42911v3" description=""/> 

 <outputtimestep value="Year"/> 

 <outputvmtdata value="true"/> 

 <outputsho value="true"/> 

 <outputsh value="true"/> 

 <outputshp value="true"/> 

 <outputshidling value="true"/> 

 <outputstarts value="true"/> 

 <outputpopulation value="true"/> 

 <scaleinputdatabase servername="" databasename="c04023y2008_in20110329" description=""/> 

 <pmsize value="0"/> 

 <outputfactors> 

 <timefactors selected="true" units="Years"/> 

 <distancefactors selected="true" units="Miles"/> 

 <massfactors selected="true" units="Pounds" energyunits="Million BTU"/> 

 </outputfactors> 

 <savedata> 

 </savedata> 
30 

 <donotexecute> 

 </donotexecute> 

 <generatordatabase shouldsave="false" servername="" databasename="" description=""/> 

 <donotperformfinalaggregation selected="false"/> 

 <lookuptableflags scenarioid="" truncateoutput="false" truncateactivity="false"/> 

</runspec> 
1 

2008 and 2011 PM10 

Emissions Inventories 

Nogales Municipality 

State of Sonora, Mexico

U.S. Environmental Protection Agency 

Region 9

Draft Final, April 24, 2012 
This page is intentionally blank. 
2 

Contents 

1. Introduction............................................................................................................................3 

2. The Nogales Municipality, Sonora, Mexico and the Nogales NAA, Arizona.......................4 

3. Source Data Summary ...........................................................................................................6 

4. Emissions Inventory Methodology........................................................................................8 

 4.1 Overview of Source Category Emission Estimate Development.......................8 

 4.2 Point Sources Estimate ..............................................................................................8 

 4.3 Area Sources Estimates.......................................................................9 

 4.4 Mobile Sources Estimate .........................................................................................15 

 4.5 Nonroad Sources Estimate..................................................................16 

5. Emissions Inventory Results and Discussion ......................................................................17 

References......................................................................................................20 
3 

1. Introduction 

1.1 Purpose 

This document provides an estimated PM10 emission inventory for all PM10 sources within the 

Nogales Municipality, State of Sonora, Mexico and the details concerning the derivation of those 

emissions estimates. EPA has created this PM10 emissions inventory to support the Arizona 

Department of Environmental Quality’s (ADEQ) work on a PM10 State Implementation Plan (SIP) 

for the Nogales PM10 Non-attainment Area (NAA), located in Santa Cruz County, Arizona. 

Specifically, an estimate of PM10 emissions is needed to determine if the Nogales NAA would 

have attained the PM10 National Ambient Air Quality Standard (NAAQS) but for emissions 

emanating from sources in the Nogales Municipality. 

1.2 Sources of PM10 

PM10 refers to particulate matter of ten microns or less in aerodynamic diameter. Another class of 

particles, denoted as PM2.5 also called fine particulate, refers to particles of 2.5 microns or less in 

aerodynamic diameter. PM10 includes both PM2.5 and the particulates with aerodynamic diameter 

between 2.5 and 10 microns. Sometimes referred to as PM2.5-10, this larger fraction is called 

“coarse” particulate. While fine particles originate mostly from combustion sources and secondary 

aerosol generation processes, coarse particles usually originate from mechanical activities and 

fugitive source categories. Typical major sources of PM10 include fugitive dust, open burning 

including wild fires, mineral crushing and grinding operations, agricultural activities such as land 

tilling, dust suspended from vehicle travel on paved and unpaved roads and, to a lesser extent, fuel 

combustion sources and mobile source exhaust. 

1.3 Emissions Inventory Overview 

The emissions data for this inventory came from two primary sources and was estimated in part 

using data or methods from these and other cited sources: 

1. “Mexico National Emissions Inventory, 1999: Six Northern States”, Final, April 30, 2004, 

prepared by Eastern Research Group (ERG), Acosta Y Asociados, and Transengineering, 

for the Secretariat of the Environment and Natural Resources and the National Institute of 

Ecology of Mexico, the United States Environmental Protection Agency, the Western 

Governors’Association, and the North American Commission for Environmental 

Cooperation. (1999 Mexico NEI) 

2. “Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 

2030”, Final, January 9, 2009, prepared by Eastern Research Group, Inc. (ERG) for the 

Instituto Nacional de Ecologia, Mexico City, Mexico, the National Renewable Energy 

Laboratory, and the United States Environmental Protection Agency, with assistance from 

the Western Governors’ Association. (2008-12 NEI Projections) 

These sources were supplemented by emissions estimates using data from emissions inventories 

from other areas in the United States (U.S.)/Mexico border area and by calculated emissions 

estimates using EPA AP-42 emissions factors for unpaved and paved road emissions.1

 We describe 

 

1

 See sections 4.3.2.1 and 4.3.2.2 for AP-42 emission factor equations and discussion of inputs. 
4 

in detail within Sections 3 and 4 the methodology used to compile emissions source category 

estimates. Mexico population data used in this emissions inventory was taken from census data at 

the Instituto Nacional de Estadistica Geografia e Informatica, (INEGI), www.inegi.mx.org. We 

used population data from 1995, 2000, 2005, and 2010. 

2. The Nogales Municipality, Sonora, Mexico and the Nogales NAA, Arizona 

 

2.1 Geography of the Area 

The combined communities of Nogales, Arizona and Nogales, Sonora, or Ambos Nogales are 

located within the Sonoran Desert. This desert covers 120,000 square miles with a minimum 

elevation of 2,500 feet and is in the Basin and Range topographic province. This topography is 

characterized by north-south elongated valleys surrounded by mountain ranges. Ambos Nogales is 

located in such a north-south valley created by the Nogales Wash running north to the Santa Cruz 

River. 

 

From south to north, Nogales Municipality is roughly analogous to a U.S. county and covers a 

632.5 square mile area along the U.S./Mexico border.2

 The largest urban center in the municipality 

is the City of Nogales, Sonora. Nogales, Sonora, Mexico lies directly south of Nogales, Arizona 

across the international border. Collectively referred to as Ambos Nogales, the communities of 

Nogales, Arizona and Nogales, Sonora, Mexico comprise the largest international border 

community in Arizona, with a combined population of 232,550 inhabitants in 2010.3

 The majority 

of the Nogales Municipality population live within the city of Nogales, Sonora. The mean 

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

 At 5,380 feet, the highest elevation 

area in Nogales, Sonora are in the Cerro de los Nogales (Nogales Hill), west of where the Obregón 

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

The Alvaro Obregón Boulevard, Luis Donaldo Colosio Boulevard, and the Corredor Fiscal toll 

road are the main transportation routes in Nogales, Sonora. The Alvaro Obregón Boulevard runs 

the length of the narrow Nogales Wash valley, and is a highly congested route used by local and 

some cross-border commercial traffic. The Corredor Fiscal is a toll road for cross-border 

commercial traffic; its on- and off-ramp access is limited to the border junction at Mariposa Road 

and a point just outside of the southern city limits of Nogales, Sonora. The Corredor Fiscal 

conducts the majority of the U.S. and Mexico cross-border commercial traffic. 

Proceeding northward, the U.S./Mexico border form the southern boundary of the Nogales NAA 

and Santa Cruz County, Arizona. Near the center of the Nogales NAA, the city of Nogales, 

Arizona is sixty miles south of Tucson, Arizona in the middle and southernmost portion of Santa 

Cruz County. The city of Nogales, Arizona is the largest city in the 76.1 square mile nonattainment 

area.5

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

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

 

2

 Municipality land area was calculated by EPA using GIS software. 

3

 Nogales, Arizona had 20,017 inhabitants and Nogales, Sonora, Mexico had 212,533 inhabitants. U.S. Census 

Bureau 2010 and Instituto Nacional de Estadistica Geografia e Informatica, (INEGI) 2010. 4

 “Statistical Municipal Workbook for Nogales, Sonora,” 2005 edition, INEGI. 5

 Nogales NAA land area was calculated by EPA using GIS software. 
5 

Figure 1: Nogales Municipality and Ambos Nogales Urban Areas. 
6 

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. 

Major highways in the Nogales, Arizona area are Arizona State Route 82, which connects Nogales, 

Arizona with Patagonia, Arizona (19 miles) and Sonoita (31 miles) to the northeast, and U.S. 

Interstate 19 which connects Tucson, Arizona to Nogales, Arizona and continues south into 

México, where it becomes Federal Highway 15. 

3. Source Data Summary 

3.1 The 1999 Mexico National Emissions Inventory 

The Nogales Municipality emissions inventory developed here is based on modifications to the 

1999 Mexico NEI estimate for the Nogales Municipality and allocations from the 2008-12 NEI 

Projections. For the Nogales Municipality, the 1999 Mexico NEI provided PM10 emissions 

estimates in four broad source categories: point, area, mobile, and non-road mobile; see Table 1 

below. More individual source category detail was added at the State of Sonora and national scale 

of analysis; for example, detailed point and area source information was provided for the State of 

Sonora. For later use and comparison, the State of Sonora emissions estimates are provided below 

in Table 2. We have provided the PM2.5 estimates here for informational and comparison 

purposes only. 

 

Table 1: Nogales Municipality PM10 and PM2.5 Emissions Inventory for 1999 (Mega-grams, 

Mg). 

Source Category PM10 PM2.5 

Point 0.8 0.0 

Area 7,815.8 1,407.2 

Mobile 22.5 18.4 

Nonroad 3.8 3.5 

Total 7,842.9 1,429.1 

Source: "1999 Mexico National Emissions Inventory: Six Northern States" Final, April 2004 

Table 2: State of Sonora, Mexico Emissions PM10 and PM2.5 Inventory for 1999 (Mg). 

Source Category PM10 PM2.5 

Point 30,880.6 14,737.2 

Area 96,766.4 22,225.9 

Mobile 236.2 193.5 

Nonroad 1,157.9 1,065.3 

Total 129,041.1 38,221.9 

Source: "1999 Mexico National Emissions Inventory: Six Northern States," Final, April 2004 
7 

3.2 1999 Mexico National Emissions Inventory and 2008 and 2012 Projections 

The 2008-12 NEI Projections provided national level emission estimates for the years 2008 and 

2012, as well as aggregate detailed information on the source categories. The document also 

estimated 2030 emissions, but those were not relevant to this analysis. See Table 3 below. 

Table 3: Mexico PM10 Emissions Inventory for 1999, 2008, and 2012 (Mg). 

Source Category 1999 2008 2012

Point 297,264 359,919 388,825

Area 439,253 483,735 443,800

Mobile 20,567 31,890 34,019

Nonroad 37,240 40,447 42,734

Source: “Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 2030” 

3.3 Population 

This section presents the population estimates for Mexico, the State of Sonora, and the Nogales 

Municipality. We used Mexico population data from the national census at the Instituto Nacional 

de Estadistica Geografia e Informatica, (INEGI) website, www.inegi.mx.org. Using population 

data from the 1995, 2000, 2005, and 2010 Mexico census, we interpolated population estimates for 

1999, 2008, 2011, and 2012; these estimates are provided below in Table 1. The 1999 population 

estimates were interpolated using 1995 and 2000 census data. The 2008 population estimates were 

interpolated using 2005 and 2010 census data. The 2011 and 2012 population estimates were 

forecasted from the 2010 census data assuming the same increment of annual increment growth for 

the period 2005 to 2010. 

Table 4: Population Data for Selected Years: 1995 to 2012. 

Population Data for 1995, 2000, 2005, and 2010 with Interpolated or Projected Values for 1999, 2008, 2011, and 2012 

1995 1999 2000 2005 2008 2010 2011 2012 

Mexico 91,158,290 96,218,388 97,483,412 103,263,388 108,707,278 112,336,538 114,151,168 115,965,798 

State of Sonora 2,085,536 2,190,682 2,216,969 2,394,861 2,555,432 2,662,480 2,716,004 2,769,528 

Nogales Municipality 133,491 154,528 159,787 193,517 209,582 220,292 225,647 231,002 

Source for 1995, 2000, 2005, and 2010 census data: INEGI 

3.3.1 Population Based Allocation Ratios 

Where applicable, we allocated 2008 and 2012 national emissions projections based on the Nogales 

Municipality’s share of national population growth. The exceptions were the Nogales Municipality 

point source estimate and the area source estimates for paved and unpaved road emissions, 

agricultural burning, and agricultural tilling emissions. These exceptions are discussed in Section 

4. 

The population-based allocation values for scaling a municipality share of national emissions 

growth were as follows: 

(1) for the period 1999-2008, 4.41 x 10-3; and, 

(2) for the period 2008-2012, 2.95 x 10-3. 
8 

These ratios were calculated using the following formula: 

Ratio 1999-2008 = (Nogales2008 - Nogales1999) / (Mexico2008 – Mexico1999); 

Ratio 2008-2012 = (Nogales2012 – Nogales2008) / (Mexico2012 – Mexico2008); 

where NogalesXXXX and MexicoXXXX are INEGI population estimates for the respective year. 

4. Emissions Inventory Methodology 

4.1 Overview of Source Category Emissions Estimates Development 

The 1999 Mexico NEI provided PM10 emissions estimates for all four major source categories, 

point, area, mobile, and non-road at three levels of analysis: national, state, and municipality; and, 

it provided more detailed area source category emissions estimates at the national and state levels 

of analysis. The 2008-2012 NEI Projections provided national estimates in detail, but did not 

provide disaggregated data at the state or municipality level of analysis and did not provide 

estimates for unpaved and paved road emissions. 

To summarize, we estimated emissions as follows: 

 for point sources we used a combined scaling methodology to provide an estimated range; 

 for area sources, we scaled most source categories by population; we calculated directly 

unpaved and paved road emissions; and, we scaled agricultural emissions by land area; 

 for mobile and nonroad sources, we scaled by population. 

Each section below describes in detail how we estimated municipality emissions for each of the 

major source categories using source document information and other cited source data. 

4.2 Point Sources Estimate 

The 1999 Mexico NEI estimated point source emissions for the Nogales Municipality at 0.8 Mg of 

PM10. The 1999 Mexico NEI and the 2008-12 Projections did not specify either the sources that 

composed this estimate, or their respective locations at the municipality level. The 1999 Mexico 

NEI provided specific point source data at the State of Sonora level, but no location information. 

For Sonora, the 1999 Mexico NEI showed 30,888.6 Mg of PM10 from 51 point sources: 97 

percent of these emissions came from 11 mines, seven utilities, and three primary metal 

manufacturing facilities.6

 The remaining three percent of emissions came from 30 other sources, 

manufacturing facilities. This suggests that in 1999 it was unlikely that a large mining, utility, 

metal manufacturing source was located in the Nogales Municipality given the very low reported 

total municipality point source emissions (0.8 Mg), compared to the average individual source 

emissions in these three largest source categories, mining, utilities, and primary metal 

manufacturing (1,426.8 Mg). 

Lacking existing source type or location data, we estimated a range of point source projections 

using two scaling calculations: 

(1) scaling the same rate of national growth to the municipality level; and, 

(2) scaling the relative national emissions increment by population ratios in Section 3.3.1. 

 

6

 Page B-5, "1999 Mexico National Emissions Inventory: Six Northern States," Final, April 2004. 
9 

For example, for the period 1999 to 2008 national point source emissions grew 21.1 percent, so 0.8 

Mg was multiplied by 1,211 to get 0.97 Mg. To apply a population growth ratio for the 1999-2008 

period, we calculated the national point source emissions growth increment, 62,655 Mg and 

multiplied it by 0.00441, and added that municipal share of national point source emissions growth 

to 0.8 Mg. to get 277 Mg in 2008. 

Table 5: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Point Sources (Mg). 

Scaling Method 1999 2008 2012 

National Emissions Growth 0.8 0.97 1.04 

Population Ratio 0.8 277 362.3 

4.3 Area Sources Estimates 

The 1999 Mexico NEI estimated area source emissions for the Nogales Municipality at 7815.8 Mg. 

Unfortunately, the 1999 Mexico NEI and the 2008-12 Projections did not specify the sources that 

composed this estimate at the municipality level. The 1999 Mexico NEI provided specific area 

source data at the State of Sonora level of analysis and we reviewed that information to see which 

sources composed this estimate; see Table 6 below. 

Table 6: State of Sonora Area Source Category Emissions by Source, 1999 (Mg). 

Area Source PM10 Share 

Unpaved Road Dust 61,049.3 63.1% 

Paved Road Dust 26,516.5 27.4% 

Agricultural Burning 4,120.0 4.3% 

Agricultural Tilling 1,959.3 2.0% 

Residential Fuel Combustion-Wood 1,529.3 1.6% 

Open Burning - Waste 582.7 0.6% 

Construction Activities 222.2 0.2% 

All others/Remainder 787.1 0.8% 

Total 96,766.4 

Source: "1999 Mexico National Emissions Inventory: Six Northern States," Final, April 2004

Three observations suggested our approach for estimating area source emissions for the Nogales 

Municipality. First, the Nogales Municipality area source estimate was an even larger proportion 

(99.7 percent) of total emissions compared to the same State of Sonora proportion (75 percent); see 

Tables 1 and 2 for area source estimates. Second, the 1999 Nogales Municipality distribution of 

area source types would not differ markedly and would be a subset of the known State of Sonora 

distribution of area source categories. Third, the largest proportion of area source emissions in 

either the State of Sonora or Nogales Municipality was in two source categories, unpaved and 

paved road dust. We, therefore, decided to do the following: 

(1) estimate directly unpaved and paved road emissions for the Nogales Municipality; 

(2) disaggregate to the municipality level the remaining State of Sonora area source categories 

in Table 6 and adjust them, where possible, by local information; and, 

(3) allocate the 2008 and 2012 national emissions projections for our selected area source 

categories based on the Nogales Municipality’s share of national population growth, except 

for agricultural emissions which were allocated by a land area scaling. Table 7 shows the 

national estimated emissions for the source categories analogous to those in Table 6. 
10 

Table 7: Selected Mexico Area Source Category Emissions: 1999, 2008, 2012 (Mg). 

Source Category 1999 2008 2012 

Agricultural Burning 13,975 14,059 14,059 

Agricultural Tilling 109,866 119,206 119,206 

Residential Fuel Combustion-Wood 226,897 238,550 199,340 

Open Burning - Waste 20,425 22,432 23,122 

Construction Activities 9,448 10,664 11,093 

Remainder of Area Sources 58,642 78,824 76,980 

Source: “Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 2030” 

4.3.1 Disaggregated 1999 Area Source Baseline Estimates for Nogales Municipality 

Before proceeding with calculating unpaved and paved road emissions and estimating 2008 and 

2012 emissions for the remaining area source categories, we developed the disaggregated 1999 area 

source baseline estimates for the Nogales Municipality. 

To provide a 1999 baseline emissions estimate for use in calculating 2008 and 2012 emissions 

estimates for the agricultural burning and tilling source categories, we proportionally scaled the 

Sonora emissions for these source categories by the 2010 Nogales Municipality proportion (195) of 

Sonora (565,297) total harvested hectares7

, 0.000345, to get the following results: 

 agricultural burning, 1.42 Mg; 

 agricultural tilling, 0.676 Mg. 

To the degree that the total harvested hectares in Nogales Municipality have grown from 1999 to 

2010 relative to the Sonora total, then using a 2010 based ratio to estimate 1999 emissions may 

introduce some double-counting of these source category emissions. 

To provide a Nogales Municipality 1999 baseline emissions estimate for the residential wood 

combustion, open burning of waste, construction activities, and the remaining area source 

categories, we proportionally scaled the State of Sonora emissions for these source categories by 

the 1999 Nogales Municipality proportion of the State of Sonora population, 0.071, to get the 

following results: 

 residential wood combustion, 107.87 Mg; 

 open burning of waste, 41.1 Mg; 

 construction activities, 15.67 Mg; and, 

 remaining area source categories, 55.52 Mg. 

For comparison purposes, we calculated the Nogales Municipality 1999 unpaved and paved road 

emissions at 4,923.6 Mg and 2,648.1 Mg, respectively, using the same emission factor input data as 

the 1999 Mexico NEI and updated 2006 and 2011 EPA AP-42 emission factor equations for 

unpaved and paved road dust. 

 

7

 Information was taken from the INEGI website: www.inegi.org.mx. 
11 

Finally, as a check against our area source category disaggregation calculations we compared the 

total of our disaggregated 1999 area source emissions estimate with the total area source estimate 

reported in the 1999 Mexico NEI: 

 estimated 1999 area source baseline total, 7,793.97 Mg; 

 1999 Mexico NEI estimate, 7,815.8 Mg. 

The difference between the two emissions estimates is 21.9 Mg., or 0.28 percent. 

4.3.2 Unpaved and Paved Road Estimates Overview 

Unpaved and paved road emissions estimates begin with an equation of the form: 

PM10 emissions = [(Total VKT) (VKT percent paved or unpaved)] x EFpaved or unpaved, 

where VKT is vehicle kilometers traveled and EF is the calculated emissions factor 

(grams/kilometer). A primary input to both unpaved and paved emissions estimates are VKT and 

the percentage of kilometers miles traveled on unpaved versus paved roads. 

For the Nogales Municipality, we could not locate publically available VKT estimates derived from 

transportation demand modeling. Consequently, as was done in the 1999 Mexico NEI, we used a 

4.3 VKT per person per day rate multiplied by population to get a daily VKT estimate. In the 1999 

Mexico NEI, the 4.3 VKT per person per day rate was used to estimate VKT for cities ranging in 

size from 100,000-250,000 population, and represented the “large town rate”.8

 

For the Nogales Municipality, the 1999 Mexico NEI used an unpaved/paved road VKT split of 8/92 

percent estimated for the “large town” population category of 100,000-250,000.9

 We could not 

locate subsequent publicly available estimates of for unpaved/paved road mileage splits for the 

Nogales Municipality. Beginning in 2005, the City of Nogales, Sonora instituted a program to pave 

unpaved roads using funds provided to the Municipality by the North American Development 

Bank.10 The “2005 Mexicali Emissions Inventory” (2005 Mexicali EI) provided the following 

unpaved/paved road VKT splits: urban road miles, 2/98; suburban road miles, 6.1/93.9; and rural 

road miles, 10.3/89.7.11 To provide a consistent and conservative estimate of unpaved and paved 

road emissions, we used the 6/94 unpaved/paved percentage VKT as a midpoint value from the 

Mexicali information and to account for an increase in paved roads within the Nogales 

Municipality since 1999. For comparison, the 1999 Mexico NEI used a 3/97 VKT split for the next 

higher “small city” size category. Our estimated range of emissions for unpaved and paved roads 

 

8

 pages 5-3 to 5-5 and Appendix A, “1999 Mexico NEI: Six Northern States,” April 2004 Final. To 

summarize, per capita per day VKT estimates were developed using transportation engineering gravity 

modeling of seven representative urban areas varying by population size. 

9

 “Estimation of Paved and Unpaved Road Dust in Mexico”, presentation by Marty Wolf, Paula Fields, and 

Salvador Gonzalez-Ayala, at NARSTO Emissions Inventory Conference, October 14-17, 2003. Unpaved and 

paved road area and VKT splits were calculated for seven representative urban areas using GIS, field 

mapping, satellite images, or aerial photographs. 

10 The North American Development Bank provided $17million to pave 300,000 square meters of urban 

streets in residential areas. www.nadb.org. 

11 Table 10, page B-19, “2005 Mexicali Emissions Inventory”, Final Report, February 27, 2009, Eastern 

Research Group, Inc. (ERG). 
12 

will be generated by the difference between the input data for the respective emission factor 

calculations; the input data and those differences are discussed below. 

A third common input factor to each unpaved and unpaved emissions factor calculation is the mean 

number of precipitation days with greater than 0.1 inch of precipitation. For the Nogales 

Municipality estimate, we used 55 precipitation days, as reported by the National Weather Service 

for Nogales, Arizona. 

4.3.2.1 Unpaved Road Estimate 

To calculate unpaved road emissions, we used the EPA AP-42, Chapter 13.2.2, November 2006, 

Final, emissions factor equation: 

EF (lb/VMT) = [(k((s/12)^1) ((S/30)^0.5) / (M/0.5)^0.2) -C] x [(365 - p)/365] 

where k = 1.8 pound of PM10/Vehicle Mile Traveled (VMT), a constant supplied with the 

equation; s = silt content percentage; S = vehicle speed; M = moisture content; C = a constant for 

brake, tire wear, and exhaust emissions 0.00047; and p = precipitation days. Once we calculated 

an emissions factor in pounds/VMT, this was converted to grams/VKT for use with the metric units 

of measurement in our source documents; the conversion factor is 1 pound/VMT equals 281.9 

gram/VKT. 

Regarding vehicle speeds (S), we used 20.3 miles per hour (mph) as in the 1999 Mexico NEI. We 

did not find publically available road link vehicle speed estimates for the Nogales Municipality. As 

a check, we consulted the 2005 Mexicali EI and found that this study used the following: 11 mph, 

urban roads; 18 mph, suburban roads; and, 25 mph, rural roads. 

For moisture content (M), we used 0.26 percent, as in the 1999 Mexico NEI. We did not find any 

publically available unpaved road silt moisture content studies for Nogales Municipality. To 

compare, the average silt moisture percentage used for the Mexicali and San Luis Rio Colorado 

Emission Inventories was 0.12 and 0.18, respectively. Also, Yuma, Arizona, near San Luis Rio 

Colorado, Mexico has 17 precipitation days as compared to the 55 in Nogales, Arizona, suggesting 

the use of a higher silt moisture percentage. 

Because we held other emission factor input variables constant, silt content estimates produce the 

greatest variability in our unpaved road emissions factor. See Table 8 for a list of observed values 

we collected. 
13 

Table 8: Silt Content Percentages in U.S./Mexico Border Area PM10 Emissions Estimates. 

Study or Source Silt Content (%) Variation Reported 

1999 Mexico NEI 7.54 --- 

2005 Mexicali EI (avg)12 2.93 0.24 Minimum and 8.21 Maximum 

WASBAQS: San Luis Rio Colorado (avg)13 0.76 0.34 Minimum and 1.85 Maximum 

Nogales Planning Area (ADEQ) 7.05 --- 

Douglas /Paul Spur Planning Area (avg)(ADEQ) 4.7 Range reported, 1.3 to 7.0 

Pima/Yuma/Pinal (avg) (ADEQ) 7.6 Range reported, 4.3-11.0 

For our estimate range, we used 2.93 and 7.54 percent as minimum and maximum estimates for silt 

content percentage as they represent observed values in Mexico Border cities, Mexicali and Ciudad 

Juarez, respectively. For comparison. the average low of all studies was 3.46 percent and the 

average high of all studies was 7.11 percent; where no high or low was reported we used the point 

estimate in both averages. The ADEQ reported values were used in past air quality planning 

estimates for these areas, but we were unable to confirm the source data. Our calculation results 

are shown below: 

 using the variables described above and a 2.93 percent silt content percentage, we calculate 

a 0.34956 lb/Vehicle Mile Traveled, or a 98.540 grams/VKT emissions factor; and, 

 using the variables described above and a 7.54 percent silt content percentage, we calculate 

a 0.90017 lb/Vehicle Mile Traveled, or a 253.76 grams/VKT emissions factor. 

Table 9: Nogales Municipality 1999, 2008, and 2011 PM10 Emissions: Unpaved Roads (Mg). 

Silt Content Percentage 1999 2008 2011 

Low Estimate: 2.93% --- 1,944.8 2,093.9 

High Estimate: 7.54% 4,923.6 5,008.3 5,392.2 

Note: the 1999 estimate used a 8/92 percent, unpaved/paved road VKT split per 1999 Mexico NEI. 

4.3.2.2 Paved Road Estimate 

To calculate paved road emissions, we used the EPA AP-42, Chapter 13.2.1, January 2011, Final, 

emissions factor equation: 

EF (lb/VMT) = [(k(sL)^0.91) x (W^1.025)] x [1- (p/4N)] 

where k = 0.0022 pound of PM10/Vehicle Mile Traveled (VMT), a particle size multiplier constant 

supplied with the equation; sL = silt loading in grams/square meter; W = vehicle weight (average); 

p = precipitation days; and N = days in period of interest, in this case 365 or one year. As stated 

above we used 55 for precipitation days. Once we calculated an emissions factor in pounds/VMT, 

this was converted to grams/VKT for use with the metric units of measurement in our source 

documents; the conversion factor is 1 pound/VMT equals 281.9 gram/VKT. 

For vehicle weight (W), we used an average 2.4 tons per vehicle as used in the 1999 Mexico NEI. 

 

12 Raw data values supplied by Marty Wolf, Eastern Research Group, Inc. 

13 Raw data values supplied by Marty Wolf, Eastern Research Group, Inc. WASBAQS refers to the Western 

Arizona Sonora Border Air Quality Study. 
14 

Because we held other emission factor input variables constant, silt loading observations produce 

the greatest variability in our unpaved road emissions factor. See Table 10 below for a list of 

observed values we collected. 

Table 10: Silt Loading in U.S./Mexico Border Area PM10 Emissions Estimates. 

Study or Source Silt Loading (gr/m2) Variation Reported 

1999 Mexico NEI 9.97 --- 

2005 Mexicali EI (avg)14 0.3106 0.0011 Minimum and 1.329 Maximum 

WASBAQS: San Luis Rio Colorado (avg)15 0.22285 

0.0857 Minimum and 0.6524 

Maximum 

Nogales, AZ Planning Area (ADEQ) 0.8 --- 

For our estimate range, we used 0.0857 and 1.329 grams per square meter (gr/m2) as minimum and 

maximum estimates for silt loading as they represent observed values in Mexico border cities, 

Mexicali and San Luis Rio Colorado, respectively. For comparison, the average low of all studies 

was 0.02956 gr/m2 and the average high of all studies was 0.92713 gr/m2; the 0.8 gr/m2 cited for 

Nogales, Arizona was incorporated in both averages. We did not incorporate the 9.97 value in 

these averages because it is so disparate from the other values; also, we could not obtain a copy of 

the Ciudad Juarez study so as to better understand the 9.97 gr/m2 figure to explain the large 

difference between it and other observed values. ADEQ provided values for Nogales, Arizona used 

in past air quality planning estimates for the area, but we are unable to confirm the source data and 

whether or not it derives from samples collected in Nogales, Arizona; consequently, we used a 

value of known derivation, 1.329 gr/m2. The results of our calculations are shown below: 

 using the variables described above and a 0.0857 gr/m2 silt loading, we calculate a 

0.00055523 lb/Vehicle Mile Traveled, or a 0.156520 grams/VKT emissions factor; and, 

 using the variables described above and a 1.329 gr/m2 silt loading, we calculate a 0.06728 

lb/Vehicle Mile Traveled, or a 1.897 grams/VKT emissions factor. 

Table 11: Nogales Municipality 1999, 2008, and 2011 PM10 Emissions: Paved Roads (Mg). 

Silt Loading 1999 2008 2011 

Low Estimate: 0.0857 gr/m2 --- 48.4 52.1 

High Estimate: 1.329 gr/m2 2,648.1 586.4 631.4 

Note: the 1999 estimate used a 8/92 percent, unpaved/paved road VKT split and 9.97 gr/m2 silt loading per the 1999 Mexico NEI.

4.3.3 Agricultural Burning and Tilling Estimates 

The Nogales Municipality 1999 baseline emissions estimates are as follows: 

 agricultural tilling, 0.676 Mg; and, 

 agricultural burning, 1.42 Mg. 

From 1990 to 2009, Mexico’s harvested surface area increased 4.8 percent and cultivated surface 

area increased 11.5 percent16; or, 0.24 to 0.57 percent per year, respectively. It is unknown if a 

significant portion of this national increase in agricultural activity occurred on land within the 

Municipality, but rather than hold the 1999 emissions estimates constant, we increased them by 

 

14 Raw data supplied by Marty Wolf, Eastern Research Group, Inc. 

15 Raw data supplied by Marty Wolf, Eastern Research Group, Inc. 

16 “Mexico at at glance: 2010” INEGI. 
15 

these annual percentages through 2008. There are no projected emissions increases in 2012. The 

percentage increase in cultivation was applied to tilling, while the percentage increase in harvesting 

was applied to burning. 

Table 12: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Agricultural Tilling and 

Burning (Mg). 

 1999 2008 2012 

Agricultural Tilling 0.676 0.69 0.69 

Agricultural Burning 1.42 1.49 1.49 

4.3.4 Residential Wood Burning, Open Burning, and Construction Estimates 

The Nogales Municipality 1999 baseline emissions estimates are as follows: 

 residential wood burning, 107.87 Mg; 

 open burning of waste, 41.1 Mg; and, 

 construction activities, 15.67 Mg. 

For these source categories, we allocated 2008 and 2012 national emissions projections based on 

the Nogales Municipality’s share of national population growth. Residential wood burning 

emissions estimates decrease from 2008 to 2012 due to use of cleaner burning fuels; projections 

show fuel swapping to and increased use of natural gas. Construction activity emissions estimates 

may be overstated depending on the local impact of decreased activity within the housing and 

commercial construction markets in Nogales Municipality. 

Table 13: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Residential Wood 

Combustion, Open Burning of Waste, and Construction Activities (Mg). 

 1999 2008 2012 

Residential Wood Burning 107.87 159.24 43.53 

Open Burning of Waste 41.1 49.95 51.99 

Construction Activities 15.67 21.03 22.3 

4.3.5 The Remaining Area Sources Estimate 

The Nogales Municipality 1999 baseline emissions estimate is as follows: 

 remaining area source categories, 55.52 Mg. 

For this aggregation representing the twenty-four other area source categories within the 1999 

Mexico NEI, we allocated 2008 and 2012 national emissions projections based on the Nogales 

Municipality’s share of national population growth. The 2012 decrease can be attributed again to 

decreases in other residential fuel combustion source categories as fuel swapping to cleaner fuels is 

projected to occur (e.g., from coal to natural gas). 

Table 14: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Remaining Area Sources 

(Mg). 

 1999 2008 2012 

Remaining Area Sources 55.52 144.49 139.05 
16 

4.4 Mobile Sources Estimate 

The Nogales Municipality 1999 baseline emissions estimate is as follows: 

 mobile sources, 22.5 Mg. 

For this source category, we allocated 2008 and 2012 national emissions projections based on the 

Nogales Municipality’s share of national population growth. 

The mobile source emissions estimate includes vehicle exhaust, tire wear, and brake wear 

emissions. In producing the mobile source emissions projections from 1999, the 2008-12 

projections took into account the following parameters: 

 changes in vehicle technologies and emissions due to fleet turnover; 

 new Mexican gasoline and diesel vehicle fuel standards; and, 

 implementation of Mexican emissions standards. 

The mobile source emissions estimates were generated with a MOBILE6-Mexico emissions 

model.17 Motor vehicle fuel demand projections provided the basis for estimating growth in 

vehicle usage in future year emissions.18 As discussed earlier, we independently estimated VKT to 

calculate unpaved and paved road emissions. While there appears to be a difference in 

methodology concerning projected on-road motor vehicle usage, there is no overlap in the 

emissions sources being estimated, direct vehicle emissions versus reintrained road dust. 

Table 15: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Mobile Sources (Mg). 

 1999 2008 2012 

Mobile Sources 22.50 72.41 78.7 

4.5 Nonroad Sources Estimate 

The Nogales Municipality 1999 baseline emissions estimate is as follows: 

 nonroad sources, 3.8 Mg. 

For this source category, we allocated 2008 and 2012 national emissions projections based on the 

Nogales Municipality’s share of national population growth. 

The 1999 NEI emissions estimate addressed diesel powered agricultural and construction 

equipment, only. The 2008-12 Projections used disaggregated fuel demand projections to estimate 

emissions for the transportation, industrial, commercial, and agricultural sectors. 

Table 16: Nogales Municipality 1999, 2008, and 2012 PM10 Emissions: Non-road Sources (Mg). 

 1999 2008 2012 

Nonroad Sources 3.80 17.94 24.69 

 

17 For a more detailed discussion of mobile source emissions modeling see the source document: 

“Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 2030”, Final, January 

9, 2009, prepared by Eastern Research Group, Inc. (ERG). 18 To estimate growth in on-road motor vehicle emissions over the 1999 to 2030 timeframe, the 2008-12 NEI 

Projections document relied on the “Long-range Energy Alternatives Planning System” (LEAP) to project 

gasoline and other vehicle fuel demand and use. For more information on the LEAP and its use, see 2008-12 

NEI projections document and D. Cuatecontzi (2008) “Long-range Energy Alternatives Planning System 

(LEAP) fuel projections”, National Autonomous University of Mexico, August 6. 
17 

5. Emissions Inventory Results and Discussion 

The Nogales Municipality emissions inventory results are shown below in Tables 17 and 18. Table 

17 aggregates the emissions estimates from Section 4. Table 18 provides 2008 and 2011 estimated 

PM10 emissions in tons. 

Table 17: PM10 Emissions Inventory for Nogales Municipality, 1999, 2008, 2011, 2012 (Mg). 

Source Category Range 1999 2008 2011 2012 

Point Sources Low Estimate 0.8 0.97 1.02 1.04 

 High Estimate --- 277 353.71 362.3 

Area Sources Unpaved Road Low Estimate --- 1,944.8 2,093.9 

 High Estimate 4,923.6 5,008.3 5,392.2 

Paved Road Low Estimate --- 48.4 52.1 

 High Estimate 2,648.1 586.4 631.4 

 Agricultural Tilling 0.676 0.69 0.69 

 Agricultural Burning 1.42 1.49 1.49 

 Residential Wood Combustion 107.87 159.24 42.50 43.53 

Open Burning of Waste 41.1 49.95 50.76 51.99 

 Construction Activities 15.67 21.03 21.77 22.3 

 Remaining Area Sources 55.52 144.49 135.75 139.05 

Mobile Sources 22.5 72.41 76.83 78.7 

Nonroad Sources 3.8 17.94 24.10 24.69 

Total Low Estimate --- 2461.41 2500.92 

Total High Estimate 7,821.06 6,338.94 6,731.22 

Note: The 1999 unpaved and paved road estimates were recalculated using current AP-42 emission factors equations 

and data inputs from the 1999 Mexico NEI; consequently, we did not generate 1999 high and low estimates. Please see 

section 4.3.2 and subsections for a complete discussion of unpaved and paved estimates. 

Table 18: PM10 Emissions Inventory for Nogales Municipality for 2008 and 2011 (Tons).

Source Category Range 2008 2011 

Point Sources Low Estimate 1.07 1.12 

 High Estimate 305.34 389.90 

Area Sources Unpaved Road Low Estimate 2,143.77 2,308.13 

 High Estimate 5,520.70 5,943.88 

Paved Road Low Estimate 53.35 57.43 

High Estimate 646.39 696.00 

Agricultural Tilling 0.76 0.76 

Agricultural Burning 1.64 1.64 

 Residential Wood Combustion 175.53 46.85 

Open Burning of Waste 55.06 55.95 

Construction Activities 23.18 24.00 

Remaining Area Sources 159.27 149.64 

Mobile Sources 79.82 84.69 

Nonroad Sources 19.78 26.57 

Total Low Estimate 2,713.24 2,756.79 

Total High Estimate 6,987.48 7,419.89 

Conversion factor: 1 Megagram = 1.10231 U.S. short tons (one short ton = 2000 pounds) 
18 

Because we started with 2012 national level projected estimates for most source categories, we 

scaled estimates to the municipal level first, then adjusted the municipal estimates consistent with 

the estimated decrease from 2012 to 2011 municipality population estimates, 2.37 percent. We 

calculated directly 2011 emission estimates for unpaved and paved roads; no adjustment was 

needed. Agricultural tilling and burning emissions estimates for 2011 reflected 2012 projections, 

no increase from 2008. We discuss specific issues concerning the allocated and estimated 

emissions inventory below. 

5.1 Lack of Point Source Location Data 

Neither source document, the 1999 Mexico NEI or the 2008-12 Projections, provided municipalityspecific point source information, such as source category and location. Consequently, it is not 

possible to validate the 2008 or 2012 projections with specific source information or activity levels. 

This may not introduce a large range of uncertainty, however, because the beginning baseline 

emissions estimate, 0.8 Mg, is so small in comparison to the total emissions inventory. Even with a 

two orders of magnitude increase to 80 Mg, the point source emissions estimate remains very small 

( 3.25 percent) compared to the 2008 total inventory low estimate of 2,461.41 Mg. 

5.2. Use of Nogales Municipality Specific Data 

Particularly for estimating unpaved and paved road emissions, Nogales Municipality specific data 

was not publically available. For instance, in calculating the 2008 and 2011 unpaved and paved 

road emission estimates, we used surrogate estimators for vehicle kilometers traveled and the 

unpaved/paved road split inputs. While we used reasonable and valid surrogates, having Nogales 

Municipality specific input information and activity levels would make these estimates less 

qualified. For other inputs to the unpaved and paved road emissions factor calculations, such as silt 

content and silt loading, any Nogales Municipality point estimate would result from of a range of 

samples from differently classified urban, suburban, rural areas or road way types. So, calculating 

a single emissions estimate from a range of silt content and silt loading inputs is not unusual, by 

itself. Also, where possible we used recent data collected from Mexican cities on the Mexico and 

U.S. border. 

Consolidating and projecting the “remaining area sources” category is likely to introduce an overestimate in that some of the sources may not exist in Nogales Municipality, or it may not be 

appropriate to scale all such sources by a population-based allocation. Again, only Nogales 

Municipality specific area source information would have adjudicated this issue. 

The 1999 NEI did not estimate border crossing emissions and the 2008-12 projections did not 

estimate PM10 emissions at border crossings. Consequently, while aggregate emissions were 

accounted for in the source documents, the incremental and local PM10 emissions effects at the 

border crossing was not factored into this analysis. 

Finally, the 2008 and 2012 estimated rate of PM10 emissions from road and other construction may 

be high because it is unclear whether the national emissions estimate reflected the full magnitude of 

the downturn in the local economy’s real estate sector. 
19 

5.3 Estimated Range of Emissions 

To allow for a lack of specific information for the point source category and a range of silt content 

and silt loading input variables in the unpaved and paved road categories, we generated a range of 

emissions estimates to get high and low estimates. As we explained for the silt content and silt 

loading values, any Nogales Municipality single emissions estimate would result from of a range of 

samples from differently classified urban, suburban, rural areas or road way types. So, calculating 

a single emissions estimate from a range of silt content and silt loading inputs is not unusual. The 

difference that might be anticipated would be that stratified sampling of different roadway areas 

and roadway types would contain the variability about the specific sample mean for each strata. 

Thus, depending on the sampling strategy and its execution, stratified sampling may provide for 

less variability around specific strata or overall mean point estimates. 

5.4 Overall Assessment 

This emissions inventory for Nogales Municipality provides a complete and sufficiently accurate 

inventory for the area based on the best methodology and source data publically available at the 

time the inventory was developed. Where Nogales Municipality specific data does not exist or 

could not be located, and we could not justify a singular data input, we reported a range of 

emissions estimates. In allocating national emissions to the Nogales Municipality or in estimating 

emissions, EPA has used reasonable and conservative assumptions to produce a current, 

comprehensive, and reasonably accurate PM10 emissions inventory. This emissions inventory is 

adequate for its intended use, providing an aggregate estimate of PM10 emissions originating from 

areas south of the Nogales, Arizona PM10 nonattainment area. 
20 

References

“Mexico National Emissions Inventory, 1999: Six Northern States”, Final, April 30, 2004, 

prepared by Eastern Research Group (ERG), Acosta Y Asociados, and Transengineering, for the 

Secretariat of the Environment and Natural Resources and the National Institute of Ecology of 

Mexico, the United States Environmental Protection Agency, the Western Governors’Association, 

and the North American Commission for Environmental Cooperation. (1999 Mexico NEI). 

 “Development of Mexico National Emissions Inventory Projections for 2008, 2012, and 2030”, 

Final, January 9, 2009, prepared by Eastern Research Group, Inc. (ERG) for the Instituto Nacional 

de Ecologia, Mexico City, Mexico, the National Renewable Energy Laboratory, and the United 

States Environmental Protection Agency, with assistance from the Western Governors’ 

Association. (2008-12 NEI Projections). 

“Technical Support Document for Recommendation that the Nogales, Arizona Area Be Designated 

as a PM2.5 Nonattainment Area”, Arizona Department of Environmental Quality, December 3, 

2007. 

“Estimation of Paved and Unpaved Road Dust in Mexico”, presentation by Marty Wolf, Paula 

Fields, and Salvador Gonzalez-Ayala, at NARSTO Emissions Inventory Conference, October 14-

17, 2003. 

 

“2005 Mexicali Emissions Inventory”, Final Report, February 27, 2009, Eastern Research Group, 

Inc. (ERG). 
This page is intentionally blank. 
Analysis of Ambient PM10 Levels, Topography, and 

Meteorological Data in Nogales, Arizona: 2007 - 2009 

U.S. Environmental Protection Agency 

Region 9 

Draft Final: July 20, 2012 
2

Table of Contents 

1.0 Introduction 

1.1 Purpose 

1.2 Sources of PM10

1.3 Geography of the Ambos Nogales Area 

2.0 Ambient PM10 Monitoring in Nogales, Arizona and Nogales, Sonora 

2.1 Ambient Monitors 

2.2 Selected Timeframe for Review 

2.3 Quality Assurance 

3.0 Analysis of 2007 - 2009 Exceedance Days 

3.1 Hourly PM10 Concentration, Wind Speed, and Wind Direction 

3.2 Representative Day 

3.3 Pattern and Timing of Exceedances 

3.4 Study Days 

3.5 Local Topography and Landscape 

3.6 Analyses of Wind Direction and PM10 Concentration 

3.7 Estimated 24-Hour Average Concentrations for Nogales NAA Under 

Meteorological Conditions Contributing to International Transport 

4.0 Discussion 

4.1 Disparity in Observed Ambient Values 

4.2 Long Range Transport 

4.3 Local Sources Near Nogales, Arizona Monitor 

4.4 Observations of Coarse Versus Fine Particulate Matter 

4.5 Review of 2010 and 2011 Exceedance Days 

5.0 Conclusions 

List of Tables 

Table 1: Twenty four hour PM10 concentrations on exceedance days in 2007. 

Table 2: Twenty four hour PM10 concentrations on exceedance days in 2008. 

Table 3: Twenty four hour PM10 concentrations on exceedance days in 2009. 

Table 4: Hourly PM10 concentration, wind speed, and wind direction at the Nogales, 

Arizona Post Office FEM monitor versus time for November 16, 2008. 

Table 5: Percentage of observed PM10 concentrations attributable to wind direction. 

January 1, 2007, May 22, 2008, and January 1, 2009 are excluded from the analysis of 

exceedance days (see Section 3.4 for discussion of “Study Days.”). 
3

Table 6: Ambient PM10 concentrations sorted by concentration value and wind direction, 

2007 - 2009 exceedance days 

Table 7: Average PM10 concentration for hours associated with wind direction from the 

south (135 - 224 degrees) versus all other directions for all exceedance days. 

Table 8: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year) 

Table 9: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year) 

Table 10: Estimated 24-hour Average PM10 Concentrations (μg/m3) for 29 Exceedance 

Days Weighted According to Decision Rules for Mexican Influence 

Table 11: Six Exceedance Days Where Observations Exist for Nogales AZ Monitors and 

Nogales, Sonora Monitor: 24-hour concentrations (μg/m3).

Table 12: Six Exceedance Days Where Observations Exist for Nogales AZ Monitor and 

Nogales, Sonora Monitor: Concentration Values Disaggregated by Southerly Wind 

Quadrant versus All Other Wind Directions (μg/m3).

Table 13: Twenty-four Hour PM10 and PM2.5 concentrations ( g/m3), and the ratio of 

observed PM10:PM2.5 on exceedance days at the Nogales, Arizona Post Office monitoring 

site (2007 - 2009). 

Table 14: Average PM10 concentration for hours associated with wind direction from the 

south (135 - 224 degrees) versus all other directions for 2010 exceedance days. 

List of Figures 

Figure 1: Map of Ambos Nogales area and Nogales PM-10 Nonattainment Area. 

Figure 2: Map of ambient PM10 monitors near Nogales, Arizona. 

Figure 3: PM10 exceedances at the Nogales, Arizona Post Office, by month and year. 

Figure 4: Hourly PM10 concentration at the Nogales, Arizona Post Office FEM monitor 

versus time of day for all 29 exceedances. 

Figure 5: Hourly PM10 concentration at the Nogales, Arizona Post Office FEM monitor 

versus time of day for all exceedances, excluding three study days (26 days, see Section 

3.4 discussion of study days). 

Figure 6: Hourly wind speed at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all 29 exceedances. 

Figure 7: Hourly temperature at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all 29 exceedances. 

Figure 8: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for all days (2007 - 2009). 

Figure 9: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for all 29 exceedance days. 

Figure 10: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for all exceedances, excluding May 22, 2008 (see text). 

Figure 11: Pollution rose of PM10 concentration versus wind direction at the Nogales, 

Arizona Post Office FEM monitor for all 29 exceedance days. 

Figure 12: Pollution rose of PM10 concentration versus wind direction at the Nogales, 

Arizona Post Office FEM monitor for all exceedances, excluding study days (26 days). 
4

Figure 13: Hourly PM10 concentration and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for November 16, 2008. 

Figure 14: Hourly PM10 concentration, wind speed, and temperature at the Nogales, 

Arizona Post Office FEM monitor versus time for all exceedances, excluding January 1, 

2007, May 22, 2008, and January 1, 2009 (see section 3.4). 

Figure 15: Hourly PM10 concentration and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for May 22, 2008. 

Figure 16: Hourly PM10 concentration and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for (a) January 1, 2007 and (b) January 1, 2009. 

Figure 17: Elevated Topographical View of Ambos Nogales Area from Northwest 

Perspective With Nogales, Sonora Highlighted and International Border in Red Line. 

Figure 18: Long Aerial and Elevation Transect of Nogales Arizona (shaded in yellow) 

and Nogales, Sonora (shaded in pink). 

Figure 19: Short Aerial and Elevation Transect of Nogales, Arizona (shaded in yellow) 

and Nogales, Sonora (shaded in pink). 

Figure 20: Hourly PM10 concentrations at the Nogales, Arizona Post Office FEM 

monitor versus time of day for all exceedances between January 1, 2010 and September 

30, 2011 compared to average PM10 concentrations from Figure 14 (2007 - 2009). 

Figure 21: Hourly wind speed at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all exceedances in 2010 compared to average wind speed from Figure 14 

(2007 - 2009). 
5

1.0 Introduction 

1.1 Purpose 

This document provides an analysis of ambient PM10 concentrations and meteorological 

data within the Nogales Nonattainment Area (NAA). The Arizona Department of 

Environmental Quality (ADEQ) requested that EPA provide this analysis to support 

ADEQ’s work on a PM10 State Implementation Plan (SIP) for the Nogales NAA, located 

in Santa Cruz County, Arizona. The primary purpose of this analysis is to determine how 

the area’s meteorology and topography have an effect on exceedances of PM10 National 

Ambient Air Quality Standard (NAAQS) and whether or not there is a south to north 

directional component to these exceedances; particularly, in reference to the international 

border between Nogales, Arizona and Nogales, Sonora, Mexico. 

1.2 Sources of PM10

PM10 refers to particulate matter with an aerodynamic diameter less than or equal to 10 

micrometers. PM2.5, also called fine particulate, refers to particulate matter with an 

aerodynamic diameter less than or equal to 2.5 micrometers. PM10 includes both PM2.5

and the particulates with aerodynamic diameter between 2.5 and 10 micrometers, which 

is referred to as PM10-2.5. This larger fraction is called “coarse” particulate. While fine 

particles originate mostly from combustion sources and secondary aerosol generation 

processes, coarse particles usually originate from mechanical activities and fugitive 

source categories. Typical sources of PM10 include fugitive dust, open burning including 

wild fires, mineral crushing and grinding operations, agricultural activities such as land 

tilling, dust suspended from vehicle travel on paved and unpaved roads and, to a lesser 

extent, fuel combustion sources and mobile source exhaust. 

1.3 Geography of the Ambos Nogales Area 

 

The combined communities of Nogales, Arizona and Nogales, Sonora, or Ambos 

Nogales are located within the Sonoran Desert. This desert covers 120,000 square miles 

with a minimum elevation of 2,500 feet and is in the Basin and Range topographic 

province. This topography is characterized by north-south elongated valleys surrounded 

by mountain ranges. Ambos Nogales is located in such a north-south valley created by 

the Nogales Wash running north to the Santa Cruz River. 

 

From south to north, Nogales Municipality is roughly analogous to a United States (U.S.) 

county and covers a 632.5 square mile area along the U.S./Mexico border.1 The largest 

urban center in the municipality is the City of Nogales, Sonora. Nogales, Sonora, Mexico 

lies directly south of Nogales, Arizona across the international border. Collectively 

referred to as Ambos Nogales, the communities of Nogales, Arizona and Nogales, 

Sonora, Mexico comprise the largest international border community in Arizona, with a 

 

1

 Nogales Municipality land area was calculated by EPA using GIS software. 
6

combined population of 232,550 inhabitants in 2010.2 The majority of the population 

within the Nogales Municipality lives within the city of Nogales, Sonora. The mean 

elevation in Nogales, Sonora is 4,265 feet above sea level.3 At 5,380 feet, the highest 

elevation area in Nogales, Sonora are in the Cerro de los Nogales (Nogales Hill), west of 

where the Obregón and Colosio routes meet, near the southern end of the city. 

The Alvaro Obregón Boulevard, Luis Donaldo Colosio Boulevard, and the Corredor 

Fiscal toll road are the main transportation routes in Nogales, Sonora. The Alvaro 

Obregón Boulevard runs the length of the narrow Nogales Wash valley, and is a highly 

congested route used by local and some cross-border commercial traffic. The Corredor 

Fiscal is a toll road for cross-border commercial traffic; its on- and off-ramp access is 

limited to the border junction at Mariposa Road and a point just outside of the southern 

city limits of Nogales, Sonora. The Corredor Fiscal conducts the majority of the U.S. and 

Mexico cross-border commercial traffic. 

Proceeding northward, the U.S. and Mexico border form the southern boundary of the 

Nogales NAA and Santa Cruz County, Arizona. At the lower center of the Nogales 

NAA, the city of Nogales, Arizona is sixty miles south of Tucson, Arizona in the middle 

and southernmost portion of Santa Cruz County. The city of Nogales, Arizona is the 

largest city in the 76.1 square mile nonattainment area.4 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. 

Major highways in the Nogales, Arizona area are Arizona State Route 82, which connects 

Nogales, Arizona with Patagonia, Arizona (19 miles) and Sonoita (31 miles) to the 

northeast, and U.S. Interstate 19 which connects Tucson, Arizona to Nogales, Arizona 

and continues south into México, where it becomes Federal Highway 15. 

 

2

 Nogales, Arizona had 20,017 inhabitants and Nogales, Sonora, Mexico had 212,533 inhabitants. U.S. 

Census Bureau 2010 and Instituto Nacional de Estadistica Geografia e Informatica, (INEGI) 2010.

3

 “Statistical Municipal Workbook for Nogales, Sonora,” 2005 edition, INEGI. 

4

 Nogales NAA land area was calculated by EPA using GIS software. 
7

Figure 1: Map of Ambos Nogales area and Nogales PM-10 Nonattainment Area. 
8

2.0 Ambient PM10 Monitoring in Nogales, Arizona and Nogales, Sonora 

2.1 Ambient Monitors 

Five ambient air monitors in the vicinity of Ambos Nogales were considered for this 

analysis. These monitors are described below and see Figure 2 for their locations. 

Within the nonattainment area, the Nogales, Arizona Post Office is the primary violating 

monitor location for PM10. The Nogales, Arizona Post Office monitoring site is 0.3 miles 

north of the border and this monitoring site is 0.9 miles northeast of the Nogales, Sonora 

Fire Station monitoring site. The Green Valley and Corona de Tucson monitoring sites 

are approximately 35 and 45 miles away from the U.S./Mexico border, respectively. 

Also, Arizona has operated a meteorological data collection station at the Nogales, 

Arizona Post Office monitoring site; wind speed observations discussed in our analyses 

were collected at that location. Temperature observations were collected at the Nogales 

International Airport, approximately six miles northeast of the Nogales, Arizona Post 

Office monitoring site. 

Nogales, Arizona Post Office, Met One BAM 1020 (Method Code: 122) PM10 SPMFEM (AQS ID: 04-023-0004, POC 3). The majority of the 24-hour PM10 exceedances 

measured in the Ambos Nogales area occurred at this monitor. This monitor operates 

continuously. Although this monitor is designated as a Special Purpose Monitor (SPM)

monitor, the data that it produces is appropriate to consider for regulatory purposes since 

it has been operational for more than 24 months and has a Federal Equivalency Method 

(FEM) designation.

Nogales, Arizona Post Office, Rupprecht and Patashnick Partisol 2000 (Method 

Code: 126) PM10 SLAMS-FRM (AQS ID: 04-023-0004, POC 1). This monitor is 

placed at the same station as the primary violating monitor. Unlike the continuous FEM 

monitor operating at the Nogales, Arizona Post Office, this monitor is filter-based with 

samples collected once every six days (1:6) and is designated as a Federal Reference 

Method (FRM) monitor. For most of the days that the continuous FEM monitor is 

violating, the filter-based FRM monitor does not have sample information.

Nogales, Sonora Fire Station, Sierra Anderson Lo-Volume Dichot (Method Code: 

073) PM10 Non-Regulatory-FRM (AQS ID: 80-026-0005, POC 1). The Nogales, 

Sonora Fire Station is the closest monitoring site to the Nogales, Arizona Post Office site. 

The PM10 monitor operating at this site is also a filter-based monitor with once in every 

six day sampling, but is designated as a non-regulatory FEM. This is the only PM10

monitor in Nogales, Sonora or the nearby vicinity south of the international border. 

Green Valley, Arizona, Multiple Methods, Met One BAM 1020 (Method Code: 122) 

and Rupprecht and Patashnick TEOM (Method Code: 079) PM10 SPM-FEM (AQS 

ID: 04-019-1030, POC 1). This is the closest monitor to the Nogales, Arizona Post 

Office on the U.S. side with the same scale of representation (neighborhood scale) as the 

Post Office violating monitor. This monitor operates continuously and is a SPM-FEM.
9

Corona de Tucson, Arizona, Rupprecht and Patashnick Partisol 2000 (Method 

Code: 126) PM10 SLAMS-FRM Background (AQS ID: 04-019-0008, POC 1): This 

monitor represents the nearest background site to the Ambos Nogales area. This 

monitoring site is designated as a State and Local Air Monitoring Station (SLAMS) and 

the PM10 monitor is also an FRM with filter-based samples once every six days. 

Figure 2: Map of ambient PM10 monitors near Nogales, Arizona. 
10

2.2 Selected Timeframe for Review 

The twenty-four hour PM10 NAAQS is based on the number of expected exceedances 

greater than 150 g/m3averaged over three years5. For this analysis, we considered the 

most recent and most complete three year data range available. There was a large period 

of missing data at the Nogales, Arizona Post Office PM10 SPM between March 16 and 

October 27, 2010 because of poor quality assurance and quality control results. 

Consequently, we considered 2007 to 2009 to be the most appropriate timeframe for this 

analysis. At the Nogales, Arizona Post Office monitors, PM10 data completeness for each 

quarter within the 2007 - 2009 timeframe is greater than 75 percent.

2.3 Quality Assurance 

The Corona de Tucson and the Green Valley monitors located near Tucson, Arizona are 

operated by the Pima County Department of Environmental Quality (PDEQ), while the 

Nogales Post Office and the Sonora Fire Station monitors are operated by ADEQ. PDEQ 

and ADEQ have an appropriate quality system in place for collecting ambient air 

monitoring data. EPA performed an independent Technical System Audit (TSA) of 

ADEQ’s ambient air monitoring program in September 2009 and a TSA of PDEQ’s 

ambient monitoring program in September 2011, per requirements in 40 CFR Part 58, 

Appendix A, Section 2.5. EPA assessed PDEQ and ADEQ’s compliance with 

established regulations governing the collection, analysis, validation, and reporting of 

ambient air quality data and concluded that PDEQ and ADEQ have a robust ambient air 

monitoring program. 

EPA reviewed and approved the 2011 ADEQ annual monitoring network plan on 

December 1, 2011. We found that the 2011 monitoring network plan was complete and 

met the requirements for annual network plans described in 40 CFR 58.10. 

3.0 Analysis of 2007 - 2009 Exceedance Days 

The measured twenty-four hour average PM10 concentrations on exceedance days during 

2007 - 2009 for the Nogales, Arizona Post Office FEM, FRM (filter-based monitor at the 

same location), Nogales, Sonora Fire Station (closest monitor), Green Valley, (closest 

monitor in U.S.), and Corona de Tucson, (background monitor), are listed below in 

Tables 1-3.6

 

5

 The NAAQS for all pollutants can be found at www.epa.gov/air/criteria.html . 

6

 Data was obtained via EPA’s Air Quality System (AQS), www.epa.gov/ttn/airs/airsaqs/ . 
11

Table 1: 24-hour PM10 concentrations on exceedance days in 2007. 

Date 

(2007)

Nogales, AZ 

Post Office 

FEM ( g/m3)

Nogales, AZ 

Post Office 

FRM ( g/m3)

Nogales, 

Sonora Fire 

Station ( g/m3)

Green 

Valley, AZ 

( g/m3)

Corona de 

Tucson, AZ 

( g/m3)

1-Jan 210 N/A N/A 11.9 N/A

6-Feb 180 N/A N/A 11.9 N/A

6-Mar 157 N/A N/A 24.2 N/A

15-Mar 175 N/A N/A 22.2 N/A

19-Oct 189 N/A N/A 29.5 N/A

27-Oct 210 122 159 24.9 28

2-Nov 211 190 170 29.4 32

3-Nov 170 N/A N/A 26.5 N/A

4-Nov 170 N/A N/A 30.2 N/A

6-Nov 186 N/A N/A 34.4 N/A

18-Nov 167 N/A N/A 30.8 N/A

19-Nov 177 N/A N/A 22.6 N/A

28-Nov 167 N/A N/A 22.0 N/A

24-Dec 233 N/A N/A 13.5 N/A

Table 2: 24-hour PM10 concentrations on exceedance days in 2008. 

Date 

(2008)

Nogales, AZ 

Post Office 

FEM ( g/m3)

Nogales, AZ 

Post Office 

FRM ( g/m3)

Nogales, 

Sonora Fire 

Station ( g/m3)

Green 

Valley, AZ

( g/m3)

Cornoa de 

Tucson, AZ

( g/m3)

26-Jan 204 N/A N/A 11.8 N/A

27-Feb 166 N/A N/A 14.6 N/A

18-May 169 147 126 22.2 21

22-May 217 N/A N/A 77.5 N/A

26-Oct 156 N/A N/A 25.7 N/A

31-Oct 159 N/A N/A 34.5 N/A

1-Nov 234 N/A N/A 26.3 N/A

8-Nov 167 155 119 22.5 16

16-Nov 171 N/A N/A 33 N/A

17-Nov 206 N/A N/A 25.4 N/A

20-Nov 161 150 126 26.4 23

22-Nov 179 N/A N/A 25 N/A

31-Dec 155 N/A N/A 10.7 N/A
12

Table 3: 24-hour PM10 concentrations on exceedance days in 2009. 

Date 

(2009)

Nogales, AZ 

Post Office 

FEM ( g/m3)

Nogales, AZ 

Post Office 

FRM ( g/m3)

Nogales, 

Sonora Fire 

Station ( g/m3)

Green 

Valley, AZ

( g/m3)

Cornoa de 

Tucson, AZ

( g/m3)

1-Jan 238 NULL 129 12.9 12

16-Jan 204 N/A N/A 17.8 N/A

There are no observed PM10 NAAQS exceedances at the Nogales, Arizona Post Office 

FRM on days when the FEM is not exceeding (i.e., days other than those shown in Tables 

1 - 3). 

Between 2007 and 2009, there were 29 exceedances of the PM10 NAAQS at the Nogales, 

Arizona Post Office monitoring location. See Figure 3. Of those exceedances, 14 

occurred in 2007, 13 in 2008, and two in 2009; with 27 exceedances in the October 

through March annual timeframe. Twenty-four hour PM10 concentrations on exceedance 

days varied between 155 and 238 g/m3, with some hourly measurements reaching 900 

g/m3. Finally, 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. 

Figure 3: PM10 exceedances at the Nogales, Arizona Post Office, by month and year. 

0

2

4

6

8

10

12

14

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

Exceedance Day Count

2009

2008

2007
13

3.1 Hourly PM10 Concentration, Wind Speed, and Wind Direction 

 

Complete hourly information on PM10 concentrations, wind direction, and wind speed 

can be found in the file Nogales PM10 – Concentration and Met Analysis.xlsx. 

Hourly information on temperature and diurnal plots of PM10 concentrations and wind 

speed can be found in the file Nogales PM10 – Concentration and Met Analysis.xlsx. 

The most relevant information for this analysis is presented and discussed here. 

A plot of hourly PM10 concentrations versus time of day for all exceedances is given in 

Figure 4. Three days were identified as having a significantly different diurnal pattern: 

January 1, 2007, May 22, 2008, and January 1, 2009 and are hereafter identified as “study 

days”. Twenty-six of the twenty-nine observed exceedances between 2007 and 2009 

have nearly identical diurnal patterns and are plotted separately in Figure 5. 

Figure 4: Hourly PM10 concentrations at the Nogales, Arizona Post Office FEM monitor 

versus time of day for all 29 exceedances. 

0

100

200

300

400

500

600

700

800

900

1000

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

PM10 (ug/m3)

Time (hour)

1/1/07 2/6/07 3/6/07 3/15/07 10/19/07 10/27/07

11/2/07 11/3/07 11/4/07 11/6/07 11/18/07 11/19/07

11/28/07 12/24/07 1/26/08 2/27/08 5/18/08 5/22/08

10/26/08 10/31/08 11/1/08 11/8/08 11/16/08 11/17/08

11/20/08 11/22/08 12/31/08 1/1/09 1/16/09
14

Figure 5: Hourly PM10 concentrations at the Nogales, Arizona Post Office FEM monitor 

versus time of day for all exceedances, excluding study days (26 days, see discussion in 

Section 3.4). 

Plots of hourly synthetic wind speed and temperature versus time of day for all 

exceedance days are given as Figures 6 and 7, respectively. As is shown in Figure 6, 

wind speeds were eight miles per hour (mph) or below for all exceedance days, with the 

exception of May 22, 2008, when elevated wind speeds were observed. While only one 

other monitor in Arizona and a few monitors in California exceeded the 24-hour standard 

on May 22, 2008, on the previous day, May 21, 2008, there were eight exceedances 

throughout Arizona and numerous exceedances in California and Nevada associated with 

elevated wind speeds. 

0

100

200

300

400

500

600

700

800

900

1000

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

PM10 (ug/m3)

Time (hour)

2/6/07 3/6/07 3/15/07 10/19/07 10/27/07 11/2/07 11/3/07

11/4/07 11/6/07 11/18/07 11/19/07 11/28/07 12/24/07 1/26/08

2/27/08 5/18/08 10/26/08 10/31/08 11/1/08 11/8/08 11/16/08

11/17/08 11/20/08 11/22/08 12/31/08 1/16/09
15

Figure 6: Hourly wind speed at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all 29 exceedances. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Wind Speed (mph)

Time (hour)

1/1/07 2/6/07 3/6/07 3/15/07 10/19/07 10/27/07

11/2/07 11/3/07 11/4/07 11/6/07 11/18/07 11/19/07

11/28/07 12/24/07 1/26/08 2/27/08 5/18/08 5/22/08

10/26/08 10/31/08 11/1/08 11/8/08 11/16/08 11/17/08

11/20/08 11/22/08 12/31/08 1/1/09 1/16/09
16

Figure 7: Hourly temperature at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all 29 exceedances. 

Note: Temperatures were recorded at Nogales International Airport (NIA), 7.6 miles northeast of Nogales, 

Arizona Post Office monitoring site. NIA is within the Nogales PM10 nonattainment area. 

Wind roses7are provided for non-exceedance days, all exceedance days, and exceedance 

days excluding May 22, 2008 in Figures 8, 9, and 10, respectively. The May 22, 2008 

exceedance is excluded from Figure 9 because it is the only day with observed winds 

greater than 8 mph. 

PM10 pollution roses8 for all exceedance days and exceedance days excluding the three 

study days identified in section 3.4 are given in Figures 11 and 12. 

 

7

 A wind rose shows the frequency of wind speed plotted in a polar coordinate system versus wind 

direction. 

8

 A pollution rose shows the frequency of ambient concentration plotted in a polar coordinate system versus 

wind direction. 

25

35

45

55

65

75

85

95

105 Temperature (Degrees Fahrenheit)

Time (hour)

1/1/07 2/6/07 3/6/07 3/15/07 10/19/07 10/27/07

11/2/07 11/3/07 11/4/07 11/6/07 11/18/07 11/19/07

11/28/07 12/24/07 1/26/08 2/27/08 5/18/08 5/22/08

10/26/08 10/31/08 11/1/08 11/8/08 11/16/08 11/17/08

11/20/08 11/22/08 12/31/08 1/1/09 1/16/09
17

Figure 8: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for non-exceedance days (2007 - 2009). 
18

Figure 9: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for all 29 exceedance days. 
19

Figure 10: Wind rose of wind speed versus wind direction at the Nogales, Arizona Post 

Office FEM monitor for all exceedances, excluding May 22, 2008 (see section 3.1). 
20

Figure 11: Pollution rose of PM10 concentration versus wind direction at the Nogales, 

Arizona Post Office FEM monitor for all 29 exceedance days. 

2007-09 Nogales 29 day po Nogales 29 day pollution rose llution rose
21

Figure 12: Pollution rose of PM10 concentration versus wind direction at the Nogales, 

Arizona Post Office FEM monitor for all exceedances, excluding study days (26 days). 

3.2 Representative Day 

For illustration, we identified November 16, 2008 as representative of the concentration, 

wind speed, and wind direction pattern observed on 26 of the exceedance days (excluding 

January 1, 2007; May 22, 2008; and January 1, 2009). The synthetic wind direction 

(SWD; in degrees, where 0 degrees is wind from the north and 180 degrees is wind from 

the south, etc.), synthetic wind speed (SWS; in meters per second and miles per hour), 

and hourly PM10 concentration ( g/m3

) for November 16, 2008 is provided in Table 4 

below. 

2007-09 Nogales 26 day pollution rose
22

Table 4: Hourly observations of wind direction, wind speed, and PM10 concentration at 

the Nogales, Arizona Post Office FEM monitor for November 16, 2008. 

Hour SWD 

(degrees) SWS (m/s) SWS (mph) PM10 ( g/m3

)

12:00:00 AM 183 0.4 0.9 222

1:00:00 AM 163 0.4 0.9 147

2:00:00 AM 180 0.5 1.1 126

3:00:00 AM 159 0.6 1.3 114

4:00:00 AM 225 0.3 0.7 64

5:00:00 AM 216 0.3 0.7 63

6:00:00 AM 168 0.5 1.1 74

7:00:00 AM 296 0.3 0.7 70

8:00:00 AM 59 0.9 2.0 43

9:00:00 AM 12 1.3 2.9 39

10:00:00 AM 14 2.1 4.7 43

11:00:00 AM 64 2.1 4.7 54

12:00:00 PM 86 2.5 5.6 22

1:00:00 PM 74 1.7 3.8 21

2:00:00 PM 77 1.2 2.7 21

3:00:00 PM 34 1.4 3.1 28

4:00:00 PM 70 1.2 2.7 25

5:00:00 PM 141 1 2.2 518

6:00:00 PM 196 0.9 2.0 226

7:00:00 PM 173 0.7 1.6 485

8:00:00 PM 154 0.4 0.9 556

9:00:00 PM 113 0.4 0.9 398

10:00:00 PM 181 0.7 1.6 463

11:00:00 PM 162 0.5 1.1 282

A plot of hourly PM10 concentrations and wind speed for the same day, November 16, 

2008 is shown in Figure 13. 
23

Figure 13: Hourly PM10 concentrations and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for November 16, 2008. 

3.3 Pattern and Timing of Exceedances 

3.3.1 Composite Day Using Aggregate Data 

In Figure 14, a composite day is presented showing the average PM10 concentration, wind 

speed, and temperature for each hour at the Nogales, Arizona Post Office FEM monitor 

across all 2007 - 2009 exceedances, excluding the previously identified study days 

(January 1, 2007, May 22, 2008, and January 1, 2009).

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

Wind Spped (mph)

PM10 Concentration

PM10 (ug/m3)

SWS (mph)
24

Figure 14: Average hourly PM10 concentration, wind speed, and temperature at the 

Nogales, Arizona Post Office FEM monitor versus time of day for all exceedances, 

excluding January 1, 2007, May 22, 2008, and January 1, 2009 (see section 3.4 for 

discussion of excluded days). 

3.3.2 Diurnal Pattern 

For the 26 exceedance days (29 exceedances, minus three study days), there is a strong 

pattern of decreasing PM10 concentrations in the early morning. The majority of days 

have a pronounced PM10 increase and drop-off between 6:00 am and 9:00 am, likely 

indicating a reproducible direct PM10 source, with the times generally corresponding to a 

morning commute pattern and mobile source impacts (the example day, November 16, 

2008, does not show this morning increase, which may be attributable to being a Sunday, 

with a less pronounced morning commute). The PM10 concentrations then reach their 

lowest points between 10:00 am and 4:00 pm, with corresponding increases in 

temperature and wind speed observed during those times. A pronounced spike in PM10

concentration is then observed beginning between 4:00 pm and 6:00 pm, with 

concentrations remaining high for a couple of hours and gradually dropping off towards 

midnight. The afternoon spike in PM10 concentrations correlates with to a significant 

drop in temperature, drop in wind speed, and generally a shift to variable/calm southerly 

(out of the south) winds. This is illustrated in Table 4, for November 16, 2008, where the 

spike in PM10 concentration observed at 5:00 pm corresponds to a shift in wind from 70 

degrees (out of the east northeast) to 141 degrees (out of the southeast) and a 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

50

100

150

200

250

300

350

400

450

500

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Wind Speed (mph)

PM10 (ug/m3)

Time (hour)

Concentration

Wind Speed

Temperature

Temperature (degrees Fahrenheit)

80

90

70

60

50

40

30

20

10
25

corresponding continuous, although slight, drop in wind speed between mid-day and 

evening. 

3.4 Study Days 

3.4.1 May 22, 2008 

The PM10 diurnal pattern for May 22, 2008 varies substantially from the other twenty-six 

exceedance days, with a pronounced spike in the early afternoon. PM10 concentrations 

peak around 4:00 pm with corresponding wind speeds of 17 mph. May 22, 2008 is the 

only exceedance day associated with elevated winds and, as noted above, several 

monitors throughout the Region measured PM10 exceedances on the previous day during 

periods of elevated winds. 

Figure 15: Hourly PM10 concentrations and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for May 22, 2008. 

3.4.2. January 1, 2007 and January 1, 2009 

As noted above, the PM10 diurnal pattern for January 1, 2007 and January 1, 2009, varies 

significantly from the other twenty-six exceedance days, with higher early morning PM10

concentrations contributing more strongly to the high 24-hour average. In both cases, the 

diurnal pattern after mid-day looks similar to other days, with an increase in hourly PM10

concentrations at 6:00 pm (although less pronounced than other exceedance days). 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

SWS (mph)
26

Figure 16: Hourly PM10 concentrations and wind speed at the Nogales, Arizona Post 

Office FEM monitor versus time for (a) January 1, 2007 and (b) January 1, 2009. 

3.4.3 Consideration of December 24, 2007 and December 31, 2008 

Both December 24, 2007 and December 31, 2008 are notable because they are holidays. 

These two days are do not have distinctly different diurnal patterns, since their diurnal 

PM10 concentrations closely match the patterns of other days with an afternoon increase 

in PM10 beginning after 4:00 pm. Both days are notable for their later spikes in PM10, 

however, late spikes in PM10 concentration are observed on other non-holiday 

exceedance days, such as March 6, 2007. 

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

12:00:00 

...

1:00:00 AM2:00:00 AM3:00:00 AM4:00:00 AM5:00:00 AM6:00:00 AM7:00:00 AM8:00:00 AM9:00:00 AM

10:00:00 

...

11:00:00 

...

12:00:00 

...

1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PM7:00:00 PM8:00:00 PM9:00:00 PM

10:00:00 

...

11:00:00 

...

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

SWS (mph)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0

100

200

300

400

500

600

700

800

900

1000

12:00:00 AM

1:00:00 AM2:00:00 AM3:00:00 AM4:00:00 AM5:00:00 AM6:00:00 AM7:00:00 AM8:00:00 AM9:00:00 AM

10:00:00 AM11:00:00 AM

12:00:00 PM

1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PM7:00:00 PM8:00:00 PM9:00:00 PM

10:00:00 PM11:00:00 PM

Wind Speed (mph)

PM10 Concentration

PM10 (ug/m3)

SWS (mph)

(a)

(b)
27

3.5 Local Topography and Landscape 

Elevations in the Ambos Nogales area are highest just south of Nogales, Sonora and 

decrease from south to north towards Tucson as the watershed of the Nogales Wash 

proceeds north to the Santa Cruz River. The mean elevation in Nogales, Sonora is 4,265 

feet.9

 At 5,380 feet, the highest elevation area in Nogales, Sonora is in the Cerro de los 

Nogales (Nogales Hill), west of where the Obregón and Colosio routes meet, near the 

southernmost end of the city. The City of Nogales, Arizona lies 3,865 feet above sea 

level. Nogales, Arizona rests in the Nogales Wash between the two mountain ranges, the 

Pajarito and Atascosa Mountains about seven miles west and the Patagonia Mountains 

roughly thirteen miles east. Figures 1 and 2 provide a general overview. Below, Figure 

17 provides a topographical view looking southeast towards Nogales, Sonora from an 

elevated viewpoint northwest of Nogales, Arizona. 

Figure 17, shows the urban outline of Nogales, Sonora overlying a topographical 

representation of the area. The Alvaro Obregón Boulevard runs the length of the Nogales 

Wash valley and is depicted in the figure as the longest yellow roadway running from the 

top right corner of the figure to the lower center of the figure at the international border 

(red line from running upper left to lower right) to connect with Business Interstate 19. 

There are four red markers in the figure: the two square red markers show the location of 

the Nogales, Arizona and Nogales, Sonora PM10 monitor sites; and, the two small circular 

markers show the location of the city centers of Nogales, Arizona and Nogales, Sonora. 

These four markers are also shown in Figures 18 and 19. 

In general, the urban area of Nogales, Sonora follows the elevation contours of the 

southern Nogales Wash, as opposed to a grid or square. Looking at the general 

topography depicted in Figure 17 (northwest perspective), there is a funnel created as the 

Nogales Wash falls from the higher elevations to the international border along the route 

of the Alvaro Obregón Boulevard and to Nogales, Arizona. Small side canyons extend 

off of the Nogales Wash bottom and into the hills surrounding hills the Nogales, Sonora 

city center, and to a lesser extent into Nogales, Arizona as elevations drop moving south 

to north. 

 

9

 “Statistical Municipal Workbook for Nogales, Sonora,” 2005 edition, INEGI. 
28

Figure 17: Elevated Topographical View of Ambos Nogales Area from Northwest 

Perspective, Nogales, Sonora Highlighted and International Border in Red Line. 

To examine the local topography, within Figure 18, we ran a long south to north transect 

starting outside of the Nogales Wash watershed and extending northward to the Santa 

Cruz River (see the yellow arrow and line running right to left in Figure 18). A Nogales, 

Sonora subtransect is depicted by the blue arrow and line running to the vertical yellow 

line representing the international border. A Nogales, Arizona subtransect is depicted by 

the green arrow and line running from the international border to the northern edge of the 

Nogales NAA. The shaded area in the elevation graph below the aerial picture depicts 

the elevation change from the international border to the northern boundary of the 

Nogales NAA when following the green line in the aerial picture. 

From south to north, the highest elevation of the long roadway transect is 4,331 feet at the 

southern edge of Nogales, Sonora, falling to the international border at 3,933 feet, 

continuing to the northern edge of the Nogales, Arizona PM10 nonattainment area at 

3,425 feet. The elevation continues to fall to approximately 3,100 feet along the Santa 

Cruz River watershed to the north. From the 4,331 feet high point in the transect, the 

elevation falls approximately 1200 feet from south to north across 34 miles. 

N
29

Figure 18: Long Aerial and Elevation Transect of Nogales Arizona (shaded in yellow) 

and Nogales, Sonora (shaded in pink). 

In Figure 19, a short subtransect is depicted by combining the blue and green lines in 

Figure 18 to form the blue line in Figure 19. Two sections of this subtransect also shows 

elevation declines on a south to north axis. The Nogales, Sonora section of the 

subtransect, shown from right to center, has an elevation drop of 201 feet over 4.8 miles 

to the international border (vertical yellow line), starting at the Nogales, Sonora urban 

boundary at 4,134 feet and dropping to 3,933 feet. The Nogales, Arizona section of the 

subtransect, shown from center to left, has an elevation drop of 508 feet over 10 miles 

from the international border to the northern boundary of the Nogales NAA (vertical red 

line), starting at 3,933 feet and dropping to 3,425 feet. 
30

Figure 19: Short Aerial and Elevation Transect of Nogales, Arizona (shaded in yellow) 

and Nogales, Sonora (shaded in pink). 

3.6 Analyses of Wind Direction and PM10 Concentration 

In addition to the pollution roses in Figures 11 and 12, three analyses were performed to 

examine the relationship between PM10 concentration and wind direction. The first 

analysis examined the percentage of the total observed 24-hour concentrations attributed 

to a given wind direction quadrant. The second analysis sorted hourly observed PM10

concentrations greater than 150 g/m3

into 100 g/m3bins and determined the percentage 

of hourly observations associated with each wind speed quadrant. The third analysis 

averaged the observed PM10 concentration associated with winds from the south versus 

all other directions for each exceedance day. 

In the first analysis, a weighted analysis of hourly concentration on exceedance days, 

excluding study days, January 1, 2007; May 22, 2008; and January 1, 2009, was 

performed to illustrate the percent of the total observed 24-hour concentration that is 

attributable to winds out of specific directional quadrants: northerly (315 degrees to 44 

degrees), easterly (45 degrees to 134 degrees), southerly (135 degrees to 224 degrees), 
31

and westerly (225 degrees to 314 degrees). The analysis was performed by summing 

concentration data for observations corresponding to wind speeds in a given quadrant 

(equivalent to the sum of concentrations times time, in this case a one-hour increment) 

and dividing by the sum of all concentrations (again, equivalent to the sum of 

concentrations times one-hour increments). Interpretation of this analysis has substantial 

uncertainty, given the extremely low and variable wind speeds observed for the majority 

of high PM10 concentration hours; nonetheless, the analysis illustrates broad directional 

correlations over the exceedance days. The complete analysis can be found in the file 

Nogales PM10 – Concentration and Met Analysis.xlsx. Table 5 (below) gives the 

percentage of observed PM10 concentrations attributable to each wind direction quadrant 

for all days, all exceedance days excluding the three study days, and all non-exceedance 

days. 

Table 5: Percentage of observed PM10 concentrations attributable to wind direction; 

January 1, 2007, May 22, 2008, and January 1, 2009 are excluded from the analysis of 

exceedance days (see Section 3.4 for discussion of “study days.”). 

Ambient Data Sample Northerly

(315 - 44°)

Easterly

(45 - 134°)

Southerly

(135 - 224°)

Westerly

(225 - 314°)

All Days in 2007 - 2009 11% 16% 63% 10%

Non-Exceedance Days 11% 16% 61% 10%

Exceedance Days (minus three study

days) 7% 10% 80% 3%

On all days, a large percentage (63 percent) of PM10 concentration is attributable to winds 

out of the south, which is expected given the high frequency of winds from the south (see 

the windroses in Figures 8-10), regardless of any other consideration of differences in 

population and emissions sources by wind direction. On exceedance days, the percentage 

of measured PM10 concentrations increases significantly, to approximately 80 percent 

attributable to winds from the south. This is consistent with the analysis presented above, 

where high afternoon PM10 concentrations on the exceedance days, excluding study 

days, was largely attributable to variable/slow winds out of the south. This also is 

consistent with the assertion that 24-hour PM10 concentrations observed on these days 

may not have exceeded the NAAQS if winds had not been out of the south. 

In the second analysis, hourly PM10 concentrations above 150 g/m3 were grouped by 

increasingly higher 100 g/m3

increments to determine which wind quadrant the highest 

ambient values were correlated with for all exceedance days. 

 
32

Table 6: Hourly ambient PM10 concentrations sorted by concentration and wind 

direction, 2007 - 2009 exceedance days. 

Range of Ambient Concentration Values (microgram/m3)

Wind 

Direction 

Quadrant

< 150 150 -

250

250 -

350

350 -

450

450 -

550 >= 550

Share of All 

Wind 

Direction 

Observations

Northerly

NW to NNE 27% 6% 3% 3% 3% 0% 17%

Easterly

NE to ESE 15% 16% 16% 11% 3% 8% 14%

Southerly

SE to WSW 41% 71% 72% 84% 92% 92% 57%

Westerly

SW to WNW 18% 6% 8% 3% 3% 0% 12%

Total 100 % 100% 100% 100% 100% 100% 100%

As shown in Table 6, the largest proportions of hourly values above 150 g/m3in each 

ambient value increment are from the southerly wind direction quadrant. Also, the 

proportion of high ambient values in each concentration increment observed for the 

southerly quadrant exceed this quadrant’s share of all wind direction observations by 14 

to 35 percent. In contrast, the proportion of high ambient values in each concentration 

increment for the other three wind direction quadrants are approximately equal to or less 

than their respective overall share of wind direction observations. The complete analysis 

can be found in the file Nogales PM10 – Concentration and Met Analysis.xlsx. 

In the third analysis, for each of the exceedance days, PM10 concentrations for hours 

associated with wind direction from the south (135 - 224 degrees) and all other directions 

(0 -134 degrees and 225-359 degrees) were averaged separately, with the results 

presented in Table 7. For one of the days, May 22, 2008, winds were entirely out of the 

southerly direction; therefore, no average concentration is calculated for the other 

direction assignment. 

Table 7: Average PM10 concentration for hours associated with wind direction from the 

south (135 - 224 degrees) versus all other directions for all exceedance days. 

Date

24-hour 

Concentration

Southerly Wind Quadrant 

Concentration

(135 to 224 degrees)

All Other Wind 

Direction 

Concentration

(225 to 134 degrees)

Concentration Ratio 

of Southerly Wind 

Quadrant to Other 

Wind Directions

1-Jan-2007 210 199 231 0.86

6-Feb-2007 180 228 100 2.28

6-Mar-2007 157 265 66 4.02

15-Mar-2007 175 360 65 5.54

19-Oct-2007 189 335 43 7.79

27-Oct-2007 210 301 133 2.26

2-Nov-2007 211 278 79 3.52

3-Nov-2007 170 213 128 1.66
33

4-Nov-2007 170 183 148 1.24

6-Nov-2007 186 209 119 1.76

18-Nov-2007 167 277 38 7.29

19-Nov-2007 177 216 63 3.43

28-Nov-2007 167 278 75 3.71

24-Dec-2007 233 368 45 8.18

26-Jan-2008 204 257 182 1.41

27-Feb-2008 166 251 66 3.80

18-May-2008 169 356 57 6.25

22-May-2008 217 217 No values observed ---

26-Oct-2008 156 219 53 4.13

31-Oct-2008 159 245 74 3.31

1-Nov-2008 234 369 76 4.86

8-Nov-2008 167 197 79 2.49

16-Nov-2008 171 273 69 3.96

17-Nov-2008 206 297 27 11.00

20-Nov-2008 161 225 56 4.02

22-Nov-2008 179 245 102 2.40

31-Dec-2008 155 163 117 1.39

1-Jan-2009 238 323 119 2.71

16-Jan-2009 204 247 119 2.08

Given that emissions and meteorological conditions may change throughout the day and 

we lack a continuous data stream of observations, this analysis examines whether it is 

possible that an exceedance would have occurred due to winds from directions other than 

from the southern quadrant. On two days, January 1, 2007 and January 26, 2008, average 

values from both the southern and all other wind quadrants exceed 150 g/m3

, although 

on January 26, 2008, average concentrations from the southern quadrant remains higher 

than the other directions. It should be noted that winds on all of these days, especially 

during periods of high concentration, were slow and variable. As such, it is possible that 

ambient concentrations came into the area from one direction and persisted as the wind 

direction changed. 

3.7 Estimated 24-Hour Average Concentrations for Nogales NAA Under 

Meteorological Conditions Contributing to International Transport 

In this analysis, each hourly concentration value from the 29 exceedance days in the 2007 

- 2009 study period was classified based on the likely influence from Mexico according 

to four criteria or decision rules. An hourly concentration value so classified was then 

weighted by 0.36, representing the maximum proportion of Nogales NAA emissions 

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

percent contribution from U.S. sources during those hours. Then, a 24-hour average 
34

concentration was recalculated to determine what concentration would have occurred but 

for international transport of PM10 emissions from Nogales, Sonora. 

To begin, we classified each hour of the 29 exceedance days based on the likelihood of 

significant international transport. An hourly concentration value was classified as 

influenced by international transport if it met one the following four criteria or decision 

rules related to hourly observations of wind direction, wind speed, and temperature 

change: 

1) hours with sustained (more than one hour consecutively) southerly winds greater 

than 4.5 mph (two meters/second (m/s)); 

2) hours with southerly winds or air flow and decreasing or stable temperatures 

preceded by or followed by hours with similar conditions, suggesting sustained 

down slope air flows from higher elevations south of the international border;. 

3) any hour preceded by and followed by hours with southerly wind or air flow and 

decreasing or stable temperatures, suggesting continued influence of down slope 

air flow from higher elevations south of the international border; and, 

4) surface wind speed less than or equal to 1.1 mph (0.5 m/s), preceded by or 

followed by hours with similar conditions, suggesting sustained air mass 

stagnation where PM10 emissions suspended in previous hours remain suspended 

in the stagnant air mass. 

The first rule identifies 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 rules identify daily periods influenced by down slope wind 

flow conditions usually occurring in the late afternoon and evening, indicative of 

sustained down slope air flows from higher elevations south of the international border. 

The fourth rule identifies periods of sustained air mass stagnation usually found in the 

late night and early morning hours after the early evening down slope wind or air flow 

has ebbed and before sunrise, after which wind speeds begin to increase from their 

overnight low values. 

The analysis of the Ambos Nogales emissions inventories concluded that U.S. sources are 

responsible for 18 - 36 percent of PM10 emissions in the Ambos Nogales region, per the 

2008 emission inventory figures shown below.10

 

10

 For a complete discussion of the Ambos Nogales emission inventories, see Appendix A: 2008 and 2011 

Emissions Inventory for Nogales NAA and Appendix B: 2008 and 2011 Emissions Inventories for the 

Nogales Municipality, Sonora, Mexico. 
35

Table 8: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (low estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,531 36 %

Nogales Municipality, Mexico 2,713 64 %

Total 4,244 100 %

Table 9: 2008 PM10 Emission Inventories: Nogales NAA, Arizona and Nogales 

Municipality, Mexico (high estimate) (tons per year) 

PM10 Percent

Nogales NAA, Arizona 1,531 18 %

Nogales Municipality, Mexico 6,987 82 %

Total 8,518 100 %

Therefore, for each hour that meets one of the four criteria listed above, instead of 

categorizing that hourly concentration as due entirely to Mexican sources on the basis of 

a single variable such as wind direction, a more conservative assumption is that 36 

percent of the hourly concentrations may be due to contributions from U.S. emission 

sources. For this analysis, we weighted the observed hourly concentrations by 0.36 for 

each hour that meets any one of the four criteria listed above and used this hourly 

weighted concentration to estimate the 24-hour average concentration that would have 

occurred in the Nogales NAA but for international transport. 

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 and provided in their entirety for all exceedance days in the 

table that follows. 

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.
36

Table 10: Estimated 24-hour Average PM10 Concentrations (μg/m3) for 29 Exceedance 

Days Weighted According to Decision Rules for Mexican Influence 

Date

Observed Rule 1 Rules 2 & 

3

Rules 1, 2, 

& 3

Rules 1, 2, 

3, & 4

1/1/2007 210.9 210.1 196.8 196.1 104.3

2/6/2007 180.3 180.3 115.4 115.4 106.9

3/6/2007 157.1 157.1 79.4 79.4 66.3

3/15/2007 176.0 176.0 94.4 94.4 76.8

10/19/2007 189.1 189.1 88.5 88.5 72.4

10/27/2007 210.1 208.6 114.2 114.2 88.2

11/2/2007 211.5 210.6 105.7 104.8 90.9

11/3/2007 170.9 170.9 110.7 110.7 77.9

11/4/2007 170.2 167.5 118.5 117.1 70.1

11/6/2007 186.6 180.3 101.9 101.9 77.4

11/18/2007 167.5 167.5 78.2 78.2 64.8

11/19/2007 177.6 176.5 100.7 99.7 78.4

11/28/2007 167.1 167.1 116.0 116.0 93.6

12/24/2007 233.3 233.3 124.3 124.3 89.5

1/26/2008 204.1 204.1 204.1 204.1 97.0

2/27/2008 166.0 166.0 99.1 99.1 63.9

5/18/2008 169.3 169.3 105.8 105.8 88.7

5/22/2008 217.4 78.3 145.7 78.3 78.3

10/26/2008 156.9 156.9 78.6 78.6 58.8

10/31/2008 159.7 159.7 89.9 89.9 64.9

11/1/2008 234.8 234.8 112.3 112.3 99.2

11/8/2008 167.7 166.3 85.8 85.1 70.5

11/16/2008 171.0 171.0 76.1 76.1 72.5

11/17/2008 206.7 206.7 107.3 107.3 107.3

11/20/2008 161.3 161.3 91.1 91.1 69.0

11/22/2008 179.6 177.3 95.8 93.6 69.5

12/31/2008 155.7 153.0 79.4 76.6 67.4

1/1/2009 238.4 238.4 122.7 122.7 88.7

1/16/2009 204.4 204.4 118.6 118.6 82.6

Values > 150 μg/m329 28 2 2 0

Considering the relatively large differences in emissions inventories in the Nogales NAA 

and Nogales, Sonora and the meteorology described by our conceptual model, it is likely 

that observed pollution during southerly down slope wind flows originating from 

Nogales, Sonora also contributed to observed pollution during following hours of 

sustained stagnation. With the wind direction varying under low wind speeds and stable 

temperatures, it remains possible, however, that a greater proportion of PM10 pollution 

during those hours of sustained stagnation may be coming from U.S. sources. Therefore, 

a slightly more conservative approach would be to relax our criteria by not considering 

sustained stagnation (Rule 4) and assign PM10 levels during these hours entirely to the 

Nogales NAA. Consequently, when we consider Mexican influence to only occur under 

conditions of relative high wind speeds (Rule 1) and sustained down slope wind flows 

from the south (Rules 2 and 3), two exceedance days would have been expected to occur 
37

but for international transport: January 1, 2007 and January 26, 2008. In conclusion, this 

analysis demonstrates that at least 27 of 29, and possibly all 29 exceedances of the PM10

NAAQS observed in the Nogales NAA during 2007 - 2009 can be attributed to sources of 

PM10 from across the international border. 

The observed concentrations and meteorological data for each hour of each exceedance 

day, the hourly concentration classification based on the criteria listed above, and the recalculation of the estimated 24-hour average concentrations based on the application of 

the four decision criteria are provided in the file Nogales PM10 – Concentration and Met 

Analysis.xlsx. 

4.0 Discussion 

4.1 Disparity in Observed Ambient Values 

4.1.1 Differences between Nogales, Arizona Post Office FEM and FRM 

As is shown in Tables 1 - 3, PM10 concentrations reported by the Nogales, Arizona Post 

Office FRM on exceedance days are always lower than PM10 concentrations reported by 

the co-located FEM. It is likely that the observed concentration differences are 

attributable to differences in monitoring methods, rather than quality assurance issues 

(see Section 2.3 for discussion of quality assurance review of these monitors). Data from 

the FEM, however, remains appropriate for comparison to the NAAQS. 

4.1.2 Differences between Nogales, Arizona Ambient Values and Nogales, Sonora 

Ambient Values 

As is shown in Tables 1 - 3 above and Table 11 below, within the three-year dataset, 

there were six days with both observed exceedances at the Nogales, Arizona Post Office 

FEM monitor and measurements at the Nogales, Arizona Post Office FRM and Nogales, 

Sonora Fire Station monitors. Observed concentrations at the Nogales, Sonora monitor 

are always lower than observed concentrations at the Nogales, Arizona Post Office FEM 

and, with one exception, lower than the observed concentrations at the Nogales, Arizona 

Post Office FRM. It is unlikely that the observed concentration differences are 

attributable to quality assurance issues (see Section 2.3), but it is possible that some of 

the differences in observed concentration could be attributable to differences in 

monitoring method. 
38

Table 11: Six Exceedance Days Where Observations Exist for Nogales, Arizona 

Monitors and Nogales, Sonora Monitor: 24-hour concentrations (μg/m3).

Date

24-hour Concentration At 

Nogales/AZ FEM BAM 

1020 Monitor

24-hour Concentration At 

Nogales/AZ FRM Partisol 

Monitor

24-hour Concentration At 

Nogales/Mexico Dicot 

Monitor

27-Oct-2007 210 122 159

2-Nov-2007 211 190 170

18-May-2008 169 147 126

8-Nov-2008 167 155 119

20-Nov-2008 161 150 126

1-Jan-2009 238 Null 129

Examining the six days of observations across the Arizona and Mexican monitors using 

the hourly observations at the Nogales, Arizona, FEM monitor we find the following: 

five of six days are consistent with the diurnal pattern observed for majority of 

exceedances (26 out of the 29); concentrations from the southerly wind μg/m3quadrant 

range from 197-356 μg/m3; concentrations from all other wind quadrants range from 56 -

133 μg/m3; and, the concentration ratios are consistent with our estimated pollution load 

ratios. See Table 12, below. 

Table 12: Six Exceedance Days Where Observations Exist for Nogales, Arizona Monitor 

and Nogales, Sonora Monitor: Concentration Values Disaggregated by Southerly Wind 

Quadrant versus All Other Wind Directions (μg/m3).

Date

Consistent 

With 

Observed 

Diurnal 

Pattern?*

24-hour 

Concentration

At Nogales, 

AZ FEM 

Monitor

Southerly Wind 

Quadrant 

Concentration (135 to 

224 degrees)

All Other Wind 

Directions

Concentration

(225 to 134 

degrees)

Concentration Ratio of 

Southerly Wind 

Quadrant to All Other 

Wind Directions

27-Oct-2007 Yes 210 301 (11 of 24 values) 133 2.26

2-Nov-2007 Yes 211 278 (16 of 24 values) 79 3.52

18-May-2008 Yes 169 356 (9 of 24 values) 57 6.25

8-Nov-2008 Yes 167 197 (18 of 24 values) 79 2.49

20-Nov-2008 Yes 161 225 (15 of 24 values) 56 4.02

1-Jan-2009 Varies 238 323 (14 of 24 values) 119 2.71

* The diurnal pattern used for comparison is depicted in Figure 14 and is based on the 26 exceedance day 

hourly averages for ambient concentration, temperature and wind speed. 

Also, we examined elevation differences between the Nogales, Sonora monitoring site 

and the Nogales, Arizona monitoring site to determine if a difference might account for 

some of the observed differences in concentration. The two sites varied by 

approximately 45 feet in elevation with the Nogales, Sonora monitor at the higher 

elevation of 3920 feet. Because we are unable to visit the Nogales, Sonora monitoring 

site, we are unable to evaluate further whether smaller scale and more local topographic 

effects may be enhancing the disparity in observed values. 
39

4.2 Long Range Transport 

As shown in Tables 1 to 3, on days that the Nogales, Arizona Post Office monitor is 

exceeding, there are no observed PM10 exceedances at the Green Valley, Arizona 

monitor, located between Nogales and Tucson, Arizona. On all days except May 22, 

2008, the PM10 concentrations observed at the Green Valley monitor are very low and did 

not exceed 35 g/m3

. Thus, it is unlikely that long range transport of PM10 is occurring 

from the direction of Tucson on those days (noting that for May 22, 2008, winds were 

entirely from the south and thus not from the direction of the Green Valley, Arizona 

monitor). 

4.3 Local Sources Near Nogales, Arizona Monitor 

We examined satellite and overhead photographs of an area within four kilometers 

surrounding the Nogales, Arizona Post Office monitoring site to determine if there were 

any local emission sources near enough to the monitor to greatly influence ambient PM10

values. The aerial photographs showed vehicle track-out on to paved roads, unpaved 

roads and drives, and disturbed surfaces in open areas in the area surrounding the 

monitor; especially in areas to the east and south. We observed a small materials loading 

and storage operation very near to the monitor. With only contemporaneous aerial 

photography, however, we cannot confirm how long this operation has existed at this site, 

or the timing, duration, and magnitude of its operations during our 2007 - 2009 analysis 

period. 

4.4 Observations of Coarse Versus Fine Particulate Matter 

Examining the ratio of PM10 to PM2.5 on exceedance days versus all monitored days 

provided information on the relative importance of sources that emit coarse particles 

(PM10-2.5) versus fine particles (PM2.5) on those days. In addition to the Nogales, Arizona 

Post Office PM10 SPM-FEM, a PM2.5 SPM-FEM is operated at the same site (with the 

same AQS ID: 04-023-0004, POC 3). Monitored values from both monitors are 

compared in the file Nogales PM10 – Concentration and Met Analysis.xlsx. For 2007 

through 2009, the average PM10:PM2.5 ratio on all days with valid samples was 6.24 

(standard deviation equals 2.89). For comparison, the PM10:PM2.5 ratio for exceedance 

days is given in Table 13. 

Table 13: Twenty-four Hour PM10 and PM2.5 concentrations ( g/m3), and the ratio of 

observed PM10:PM2.5 on exceedance days at the Nogales, Arizona Post Office monitoring 

site (2007 - 2009). 

Sample Date PM10 (A) PM2.5 (B) PM10/PM2.5

(A/B)

1/1/2007 210 141 1.49

2/6/2007 180 28 6.43

3/6/2007 No paired data available

3/15/2007 No paired data available
40

10/19/2007 189 22 8.79

10/27/2007 210 26 8.20

11/2/2007 211 28 7.62

11/3/2007 170 25 6.85

11/4/2007 170 23 7.33

11/6/2007 186 23 8.05

11/18/2007 167 19 8.70

11/19/2007 177 21 8.31

11/28/2007 167 23 7.20

12/24/2007 233 72 3.26

1/26/2008 204 36 5.70

2/27/2008 166 17 9.88

5/18/2008 169 21 8.13

5/22/2008 217 20 10.96

10/26/2008 156 20 7.88

10/31/2008 No paired data available

11/1/2008 234 28 8.33

11/8/2008 167 23 7.42

11/16/2008 171 24 7.18

11/17/2008 206 24 8.58

11/20/2008 161 23 7.00

11/22/2008 179 28 6.39

12/31/2008 155 62 2.48

1/1/2009 238 142 1.67

1/16/2009 204 29 7.06

With the exception of the four holidays (January 1 and December 24, 2007; December 

31, 2008; and January 1, 2009) the ratio of PM10 to PM2.5 stays approximately the same 

or increases (noting a slight decrease to 5.7 on January 26, 2008, which is within a 

standard deviation of the average and could be considered as staying the same). On the 

four holidays, the ratio of PM10 to PM2.5 decreases by more than a standard deviation 

from the average ratio, suggesting an increase in a source of fine particles, such as 

increased wood combustion. The ratio of PM10 to PM2.5 increases by the greatest amount 

on May 22, 2008, which suggests that more coarse particles and/or different sources may 

be contributing to this exceedance. 
41

4.5 Review of 2010 and 2011 Exceedance Days 

For reasons discussed in Section 2.2, we chose 2007 - 2009 for our study period. 

Nonetheless, we evaluated whether the exceedance days in 2010 and 2011 were 

consistent with the diurnal pattern we observed for exceedance days in our 2007 - 2009 

analyses. Also we did two analyses to determine if we would observe a contribution of 

high hourly ambient values from the southerly wind direction quadrant similar to what 

we observed over the 2007 - 2009 exceedance days. 

For the monitoring data reported as of the time of this analysis, i.e., through the third 

quarter of 2011, there were seven reported PM10 exceedance days in 2010 and 2011: 

December 2, 3, 4, 5, 8, and 13, 2010; and September 23, 2011. Figures 20 and 21 show 

the hourly PM10 concentration and wind speed, respectively, for those seven days versus 

the average PM10 concentration and wind speed for the 2007 - 2009 exceedances (from 

Figure 14). Wind speed data for 2011 is not yet available; consequently, September 23, 

2011 was not included in Figure 21. 

Figure 20: Hourly PM10 concentrations at the Nogales, Arizona Post Office FEM 

monitor versus time of day for all exceedances between January 1, 2010 and September 

30, 2011 compared to average PM10 concentrations from Figure 14 (2007 - 2009). 

0

100

200

300

400

500

600

700

800

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

PM10 Concentration

Average for 2007-2009 Exceedances

12/2/2010

12/3/2010

12/4/2010

12/5/2010

12/8/2010

12/13/2010

9/23/2011
42

Figure 21: Hourly wind speed at the Nogales, Arizona Post Office FEM monitor versus 

time of day for all exceedances in 2010 compared to average wind speed from Figure 14 

(2007 - 2009). 

For the six 2010 exceedance days, we performed two additional meteorological analyses 

to determine if we would observe a contribution of high hourly ambient values from the 

southerly wind direction quadrant similar to what we observed over the 2007 - 2009 

exceedance days. These analyses are similar to those described in Section 3.6 concerning 

hourly ambient concentrations and wind direction. Again, September 30, 2011 was not 

included in these analyses because wind speed and direction data are not yet available for 

2011. 

In the first analysis, on 2010 exceedance days, we determined that 87.6 percent of the 

observed 24-hour PM10 concentration is attributable to winds from the south, i.e., 135 - 

224 degrees. The remainder of the 24-hour PM10 concentration is attributed to: east, 45 - 

134 degrees, 5.9 percent; west, 225 - 314 degrees, 1.5 percent; and north, 315 - 44 

degrees, 4.9 percent. 

For the second analysis, we averaged the observed PM10 concentration associated with 

winds from the south versus all other directions for each exceedance day; see Table 14 

below (comparable to Table 7 for 2007 - 2009). Only December 4, 2010 had an hourly 

average PM10 concentration above 150 g/m3from directions other than southerly wind 

quadrant. A closer examination of hourly concentrations, wind speed, and wind direction 

on December 4, 2010, however, indicates that this is due largely to an anomaly of the 

mid-day low concentrations being attributable to southerly wind flow; an event not 

usually observed on most exceedance days. This results in the averaging of a relatively 

small number of hours for all other wind directions quadrant only during the high 

concentration, stagnant wind conditions in the early morning and late evening. 

0

1

2

3

4

5

6

7

8

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Wind Speed (mph)

Average for 2007-2009 Exceedances

12/2/2010

12/3/2010

12/4/2010

12/5/2010

12/8/2010

12/13/2010
43

Table 14: Average PM10 concentration for hours associated with wind direction from the 

south (135 - 224 degrees) versus all other directions for 2010 exceedance days. 

Date

24-hour 

Concentration

Southerly Wind Quadrant 

Concentration

(135 to 224 degrees)

All Other Wind 

Direction 

Concentration

(225 to 134 degrees)

Concentration Ratio 

of Southerly Wind 

Quadrant to Other 

Wind Directions

2-Dec-2010 177 188 57 3.33

3-Dec-2010 161 172 108 1.59

4-Dec-2010 191 184 215 0.86

5-Dec-2010 163 242 31 7.88

8-Dec-2010 159 245 40 6.19

13-Dec-2010 175 245 60 4.08

To conclude, the screening analysis of the seven reported exceedances between January 

1, 2010 and September 30, 2011, shows that all of these exceedances are consistent with 

observed exceedances during the 2007 - 2009 period. Only December 4, 2010 potentially 

deviates from the majority of exceedance days. Again, we observed a small number of 

wind direction observations from the all other wind direction quadrants were associated 

with high PM10 concentrations, leading to an average 215 g/m3PM10 concentration 

attributed to the non-southerly wind direction quadrants. However, even this exceedance 

is likely similar to the 2007 - 2009 observations and, with further analysis, may be 

attributable to emissions from Nogales, Sonora, Mexico. Therefore, the conclusions 

reached in the more sophisticated analysis of 2007 - 2009 exceedances are likely to be 

applicable to 2010 - 2011 exceedances as well, based on this screening analysis of the 

incomplete data during the later period. 

 

5.0 Conclusions 

From this review and analysis of the Nogales NAA ambient PM10 data, local 

meteorology, and topography, we draw the conclusions listed below. 

The majority of exceedances, 79 percent, occur in the October to January 

timeframe, mostly in November. Also, given the high desert environment and 

winter light regime, temperatures usually drop dramatically, 20 degrees 

Fahrenheit over the 3-4 hours after sunset. 

Elevations drop 709 feet over 14.8 miles across the south to north local transect 

we examined, from the southern boundary of Nogales, Sonora to the northern 

boundary of the Nogales NAA. 

Of the 29 exceedance days in 2007 - 2009, twenty-six of those days 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 

January 1, 2007, May 22, 2008, and January 1, 2009. 
44

On exceedance days, the largest proportions, 71-92 percent, of hourly values 

exceeding 150 g/m3and almost all of the highest observed PM10 concentrations, 

92 percent of observations above 450 g/m3, are associated with a southerly wind 

direction. 

On all 29 exceedance days, the ambient PM10 concentration attributed to the 

southerly wind quadrant exceeds 150 g/m3. In contrast, two exceedance days 

from the “all other wind direction” quadrants show a value greater than 150 

g/m3: January 1, 2007, and January 26, 2008. 

Only one of 29 exceedance days shows a concentration attributed to the “all other 

wind direction” quadrants greater than that of the concentration attributed to the 

southerly wind quadrant: January 1, 2007. 

The average ratio of the southerly wind quadrant share of 24-hour ambient PM10

values to all other wind quadrants share of ambient values is 3.83 to one. 

Considering relative high wind speeds, sustained down slope wind flows from the 

south, and sustained air stagnation, an analysis of hourly concentration values 

shows that at least 27 of 29, and possibly all 29 exceedances of the PM10 NAAQS 

observed in the Nogales NAA during 2007 - 2009 can be attributed to sources of 

PM10 from across the international border. The two exceedance days that would 

have been expected to occur were January 1, 2007 and January 26, 2008. 

On most exceedance days, the ratio of PM10 to PM2.5 increases or stays the same 

compared to the average ratio for all days in 2007 - 2009. The exceptions are four 

holidays where the ratio of PM10 to PM2.5 on exceedance days decreases, 

indicating increased importance of a combustion source. 
Appendix E 

ADEQ Technical Support Document for Control Measure Emissions Reductions 

This appendix contains ADEQ's Technical Support Document (TSD) and four supporting 

appendices. The TSD provides detailed explanation for estimated PM10 emissions reductions 

resulting from paving/double chip-sealing unpaved roads in the Nogales Nonattainment Area 

(Nogales NA). Appendix E.1 provides data used to estimate the number of annual vehicle miles 

traveled on applicable roads in the Nogales NA. Appendix E.2 includes paving/double chipsealing documentation provided by Santa Cruz County. Appendix E.3 includes a map created by 

ADEQ using the latest geographic information systems (GIS) data to depict paved and unpaved 

roads in the Nogales NA that are not within Nogales' city limits, and ADEQ's estimated mileage 

for both road types. Appendix E.4 includes before and after aerial imagery of roads paved/double 

chip-sealed in the Nogales NA. 
This page is intentionally blank. 
1

Appendix E 

ADEQ Technical Support Document for Control Measure Emission Reductions

 

E.1. Emissions Reductions from Roads Paved in Rio Rico, AZ from 2002-2008 

When ADEQ submitted the 1993 SIP for the Nogales Nonattainment Area (NA), most roads in 

the portions of Rio Rico in the nonattainment area were paved, but the community grew at a 

steady pace from that point. From 1994-2001, Santa Cruz County double-chip sealed or paved 

approximately 40 miles of roads in Rio Rico, both in and near the Nogales NA.1 

Santa Cruz County was able to provide records for 39.8 miles of roads chip sealed in Rio Rico 

between the years 2002-2008. Documentation provided by the County is in Appendix 2 of this 

document. Of these 39.8 miles of chip sealed roadways, 8.6 miles were found to be located within 

Rio Rico in the Nogales NA; Table E.1 includes the road names, year chip sealed, road length and 

mileage chip-sealed. 

Table E.1 

Road Mileage Chip Sealed in Rio Rico Since 2002 

Roadway Year Paved Road Length [mi]* Reported Mileage Paved **

Calle Arikara 2002 1.09 1 

Paseo Mexico 2004 4.03 2.6 

Calle Coyote- Annette Ct 2006 1.92 2 

Paseo Guebabi 2006 2.70 3 

 Total 9.75 8.6 

 * Calculated from aerial photography 

 **Provided by Santa Cruz County 

To estimate the emission reductions provided by 8.6 miles of chip sealing in Rio Rico, ADEQ 

estimated Annual Average Daily Traffic (AADT) for unpaved roadways by using aerial 

photography of the region to digitize roadways and categorize them as paved or unpaved. The 

number of homes on each unpaved roadway was also determined from aerial photography. 

Utilizing U.S. Department of Transportation data, we estimated vehicle trips per household for 

the Rio Rico Area as 1981 trips per year. This was calculated using the following methodology: 

Tp = Average Person trips by household = 3466 (U.S. Dpt. of Transportation, 2011, Table 5) 

TV = Average Vehicle trips by household = 2068 (U.S. Dpt. of Transportation, 2011, Table 6) 

SF = Scaling Factor = TV / TP = 2068 / 3466 = 60% 

Rio Rico CDP median household income = $43,805 (US Census State and County Quickfacts, 

median HH income for Santa Cruz County, Rio Rico CDP 2006-2010) 

TPHH = Person trips by household income = 3321 (U.S. Dpt. of Transportation, 2011, Table 8; per 

Rio Rico household income) 

 

1

 Santa Cruz County is unable to locate chip sealing records for 1994-2002; ADEQ did receive written 

confirmation of the mileage estimation from County officials. See Appendix G – Supplementary 

Information 
2

According to the U.S. Department of Transportation for a median income of $43,805 (median 

income of Rio Rico) the household has an income of 3321 trips per year. 

Vehicle trips by household income = TPHH * SF = 3321 * 60% = 1981 

If we assume the national trips taken were approximately the same for the year 2008, we can 

estimate VMT for individual unpaved roads using the calculated vehicle trips by household by 

implementing the following methodology: 

  VMTX LX TH XX  **5280/*5.0

Where: 

VMTX = Vehicle Miles Traveled for a particular roadway, X [miles] 

0.5 = Adjustment ratio to account for the location of houses along a road length and the distance 

needed to travel to exit the roadway. It is assumed that on average a vehicle must travel an 

average of one quarter of the road length before it exits the roadway and will make this trip 2 

times (once upon leaving and once upon returning) to the residence. 

LX = Length of roadway X [ft] 

5280 = conversion factor from feet to miles [ft/mile] 

HX = the number of homes located on roadway X 

TX = Average annual trips per household = 1981 

Table E.2 

Calculated VMT for Chip-Sealed Roadways in Rio Rico for 2009

Roadway Road Length 

[mi] 

Household 

Vehicle Trips 

Taken 

Households VMT 

Calle Arikara 1.09 1981 21 22694 

Paseo Mexico 4.03 1981 49 195774 

Calle Coyote- Annette Ct 1.92 1981 46 65678 

Paseo Guebabi 2.70 1981 63 168746 

Total 9.74 7924 179 452893 

Using the method outlined above, total VMT for unpaved roadways and chip-sealed roadways 

within the Rio Rico portion of the Nogales NA was found to be 968,460 miles (Appendix E.1) 

and 452,893 miles respectively (Table E.2). In order to calculate total PM10 emissions from 

unpaved roadways, ADEQ calculated unpaved road emission factors for a range of possible 

surface material silt contents within the Nogales NA using equations 1(b) and 2 from EPA AP-42 

5th Ed. Volume 1 Chapter 13.2.2. A low surface material silt content value of 2.90% and a high 

surface material silt content value of 7.50% were utilized per EPA recommendation and based on 

the Mexican NEI (2004) and the Mexicali Emission Inventory (2005). These calculations are 

shown below: 
3

   

  C

M

Ss k

E c

a d

 

5.0

3012

Where: 

E = PM10 emission factor (lb/VMT) = 0.248 lb/VMT (low value) & 0.642 lb/VMT (high 

value)

k = Empirical Constant = 1.8 lb/VMT (EPA AP-42 Chapter 13.2.2, 2006) 

s = surface material silt content (%) = 2.90 % and 7.50 % (recommended by EPA and based on 

the Mexican NEI – 2004 and the Mexicali Emission Inventory - 2005). 

M = surface material moisture content (%) = 5.23 % (No reliable surface soil moisture 

measurements are known for the area. Therefore, the average 2 inch depth soil moisture from 

Walnut Gulch, AZ NRCS Site # 2026 for the year of 2008 of 4.30% was adjusted for Nogales, 

AZ based on the average annual difference in rainfall between the two locations of 21.5% 

[Balling, 1988]) 

S = mean vehicle speed (mph) = 25 mph (Based on the typical unpaved road speed limit in 

Arizona) 

a = Empirical Constant = 1 (EPA AP-42 Chapter 13.2.2, 2006) 

c = Empirical Constant = 0.2 (EPA AP-42 Chapter 13.2.2, 2006) 

d = Empirical Constant = 0.5 (EPA AP-42 Chapter 13.2.2, 2006) 

C = 0.00047 lb/VMT (EPA AP-42 Chapter 13.2.2, 2006) 

This emission factor was then corrected to only account for non-rainy days: 

est      PEE 365/365

Where: 

Eest = annual size-specific emission factor extrapolated for natural mitigation (lb/VMT) = 

0.217 lb/VMT (low value) & 0.563 lb/VMT (high value) 

E = the unadjusted emission factor = 0.248 lb/VMT (low value) & 0.642 lb/VMT (high value) 

P = number of days in a year with at least 0.254 mm (0.01 in) of precipitation = 45 days (EPA 

AP-42 Figure 13.2.2-1., 2006) 

Using the above calculated emission factors of 0.217 lb/VMT and 0.563 lb/VMT, and the total 

VMT of 968,460 miles for all unpaved roadways in the Rio Rico portion of the Nogales NA, 

ADEQ calculated total emissions from unpaved roadways to be: 

EVMTE   miles  VMTlb   tonlb  Low EST  2000/*  /2000//217.0* 968,460 = 105 tons

EVMTE   miles  VMTlb   tonlb  High EST  2000/*  /2000//563.0* 968,460 = 273 tons

Therefore, the total PM10 emissions from unpaved roads within the Rio Rico portion of the 

Nogales NA are estimated to be between 105 and 273 tons. 
4

According to Santa Cruz County officials, a double layer of chip-seal was applied to the 

roadways in the Rio Rico portion of the Nogales NA listed in Table E.1. This type of paving has 

been estimated as having a control efficiency of approximately 90% if it is combined with paved 

shoulders, curbs and gutters (Engineering Science, 1987). In order to determine the PM10

emission reductions observed from the chip-sealing of the roadways previously mentioned, two 

separate methods of calculating emissions from chip sealed roadways are presented below. The 

two emission estimates differ in the control efficiency utilized for the chip-sealing with: Method 

1) utilizing 90% control efficiency for chip-sealed areas and Method 2) utilizing a paved road 

emission factor for the chip-sealed areas where the paved road emission factor was calculated by 

utilizing Eq. 2 from AP 42: 13.2.1-5 (EPA, 2011). 

METHOD 1 (M1) 

Method 1 utilized 90% control efficiency for those roadways which have been chip-sealed. Table 

E.3 presents the calculated emissions from these roadways assuming no control measures were 

utilized (41 tons/yr PM10 emitted when utilizing EEST-Low and 107 tons/yr PM10 emitted when 

utilizing EEST-High) and assuming all roadways were chip-sealed resulting in 90% control 

efficiency (4.1 tons/yr PM10 emitted when utilizing EEST-Low and 10.7 tons/yr PM10 emitted when 

utilizing EEST-High). In those cases where the entire road length was not chip-sealed, VMT (and 

thus PM10 emissions) was adjusted for the percentage of roadway which was chip-sealed. 

Table E.3 

Calculated PM10 Emissions Assuming 90% Chip-Seal Efficiency 

Roadway 

VMT 

Unpaved 

Emissions, 

Low [tons] 

Unpaved 

Emissions, 

High [tons] 

Chip-sealed 

Emissions, 

Low [tons] 

Chip-sealed 

Emissions, 

High [tons] 

Calle Arikara 22694 2.3 5.9 0.23 0.59 

Paseo Mexico 195774 13.7 35.5 1.37 3.55 

Calle CoyoteAnnette Ct 65679 7.1 18.5 0.71 1.85 

Paseo 

Guebabi 168746 18.3 47.5 1.83 4.75 

Total 452893 41.4 107.4 4.14 10.7 

METHOD 2 (M2)

Method 2 assumed double chip-sealed roadways would produce emission reductions to the same 

degree as asphalt paved roadways. Therefore, an emission factor was calculated for the paved 

roadways using Eq. 2 from AP 42: 13.2.1-5 (EPA, 2011). This calculation is shown below: 

       N WsLkE P

4 1 91.0 02.1



Where: 

E = annual average emission factor = 0.000841 lbs/VMT 
5

k = particle size multiplier for particle size range and units of interest = 0.0022 lbs/VMT (Table 

13.2.1-1. from AP-42, EPA 2011) 

sL = road surface silt loading = 0.105 g/m2

 (Assumed to be comparable to an average silt loading 

value measured from local traffic roads in Table 3, page 28 of Phoenix Airshed Particulate 

Emissions study, Arizona State University 2006) 

W = average weight of the vehicles traveling the road = 3 tons (Arizona State University 2006, 

pg. 27) 

P = number of "wet" days with at least 0.254 mm (0.01 in) of precipitation during the averaging 

period = 45 days (EPA AP-42 Figure 13.2.2-1., 2006) 

N = number of days in the averaging period = 365 days 

The calculated emission factor does not account for brake wear and tire wear emissions and thus, 

EPA’s Motor Vehicle Emission Simulator (EPA MOVES2010a, 2009) was run for the year of 

2008 for Santa Cruz County in order to estimate an emission factor for these processes at the 

county level. This emission factor was then added to the paved roadway emission factor above 

(0.000841 lbs/VMT). MOVES calculated an emission factor of 0.000220 lbs/VMT. When the 2 

emission factors are summed a total emission factor of 0.00106 lbs/VMT is calculated for paved 

roads in the Nogales NA. 

Table E.4 presents the emissions from these roadways assuming no control measures were 

utilized (41 tons/yr PM10 emitted when utilizing EEST-Low and 107 tons/yr PM10 emitted when 

utilizing EEST-High) and assuming all roadways were chip-sealed with a paved road emission factor 

of 0.00106 lbs/VMT (0.202 tons/yr PM10 emitted when utilizing EEST-Low and EEST-High). In those 

cases where the entire road length was not chip-sealed, VMT (and thus PM10 emissions) was 

adjusted for the percentage of roadway which was chip-sealed. 

Table E.4 

Calculated PM10 Emissions Assuming Paved Road Efficiency 

Roadway 

VMT 

Unpaved 

Emissions, Low 

[tons] 

Unpaved 

Emissions, High 

[tons] 

Paved Road 

Emissions [tons]

Calle Arikara 22694 2.3 5.9 0.011 

Paseo Mexico 195774 13.7 35.5 0.067 

Calle CoyoteAnnette Ct 65679 7.1 18.5 0.035 

Paseo Guebabi 168746 18.3 47.5 0.089 

Total 452893 41.4 107.4 0.202 

From the results calculated in Methods 1 and 2 (Tables E.3 and E.4). We can assume that the 

application of chip-seal to the 5 roadways listed resulted in the reduction of PM10 emissions 

between 37.3 and 41.2 tons per year assuming low unpaved road silt content value of (2.90 %) 

and between 96.7 and 107 tons per year assuming a high unpaved road silt content value of (7.50 

%). Conservatively, we can assume that chip-sealing the roadways reduced PM10 emissions 

within the region by 37.3 tons per year. 
6

E.2. Emissions Reductions from Roads Paved in Nogales, AZ from 1987-1996 

During analysis of aerial photography of the Nogales, AZ portion of the Nogales NA, ADEQ 

determined 11 roadways had been chip sealed between the years of 1992 and 1996. Those 

roadways identified are presented in Table E.5. PM10 emissions reductions due to the paving of 

these roadways are presented in this section. ADEQ did not include this measure to demonstrate 

attainment in the 1993 Nogales NA SIP; therefore, ADEQ is identifying this chip sealing as a 

control measure implemented in the Nogales NA. 

Table E.5 

Road Mileage Paved in Nogales Prior to 1996 

Roadway Year Paved Road Length [mi]* 

Royal Rd 92-96 0.9 

Vista del Cielo 92-96 2.2 

Hohokam 92-96 .17 

La Quinta 92-96 .75 

Yucca Drive S. 92-96 2.0 

Bristol Dr 92-96 .40 

Target Range Rd 92-96 0.2 

Frank Reed Rd 92-96 .95 

Kino Rd 92-96 .28 

Kelsey Rd 92-96 .27 

West 1st St 92-96 .32 

Total 8.4 Miles * Calculated from aerial photography 

To estimate the emission reductions provided by 8.4 miles of chip sealing in Nogales, Arizona, 

ADEQ estimated Annual Average Daily Traffic (AADT) for unpaved roadways by using aerial 

photography of the region to digitize roadways and categorize them as paved or unpaved. The 

number of homes on each unpaved roadway was also determined from aerial photography. 

Utilizing 2009 U.S. Department of Transportation data, we estimated vehicle trips per household 

for the Nogales Area as 1712 trips per year. This was calculated using the following 

methodology: 

Tp = Average Person trips by household = 3466 (U.S. Dpt. of Transportation, 2011, Table 5) 

TV = Average Vehicle trips by household = 2068 (U.S. Dpt. of Transportation, 2011, Table 6) 

SF = Scaling Factor = TV / TP = 2068 / 3466 = 60% 

Nogales, AZ median household income = $29,442 (US Census State and County Quickfacts, 

median HH income for Nogales (City), 2010) 

TPHH = Person trips by household income = 2,854 (U.S. Dpt. of Transportation, 2011, Table 8; 

per Nogales household income) 

According to the U.S. Department of Transportation for a median income of $29,442 (median 

income of Nogales) the household has an income of 2,854 trips per year. 

Vehicle trips by household income = TPHH * SF = 2854 * 60% = 1,712 
7

If we assume the national trips taken were approximately the same for the year 2008, we can 

estimate VMT for individual unpaved roads using the calculated vehicle trips by household by 

implementing the following methodology: 

  VMTX LX TH XX  **5280/*5.0

Where: 

VMTX = Vehicle Miles Traveled for a particular roadway, X [miles] 

0.5 = Adjustment ratio to account for the location of houses along a road length and the distance 

needed to travel to exit the roadway. It is assumed that on average a vehicle must travel an 

average of one quarter of the road length before it exits the roadway and will make this trip 2 

times (once upon leaving and once upon returning) to the residence. 

LX = Length of roadway X [ft] 

5280 = conversion factor from feet to miles [ft/mile] 

HX = the number of homes located on roadway X 

TX = Average annual trips per household = 1712 

Table E.6 

Calculated VMT for Chip-Sealed Roadways in Nogales Prior to 1996 

Roadway Road Length [mi] Household Vehicle Trips Taken Homes VMT 

Royal Rd 0.9 1,712 21 16178 

Vista del Cielo 2.2 1,712 85 160072

Yucca Drive S. 2 1,712 8 13696 

Bristol Dr 0.4 1,712 23 7875 

Frank Reed Rd 0.95 1,712 77 62616 

Kino Rd 0.28 1,712 16 3835 

Kelsey Rd 0.27 1,712 27 6240 

West 1st St 0.4 1,712 20 6848 

 Total 257 277360

Roadway Road Length [mi] AADT VMT 

Target Range Rd 0.2 6468 1294 

 Total 278654

Using the method outlined above, total VMT for residential chip-sealed roadways within Nogales 

was found to be 277,361 miles. Three other roadways were also identified as being chip sealed 

within Nogales. These roadways are listed below: 

1. Hohokam Dr - Public Roadway (Commercial) 

2. La Quinta Rd - Industrial Roadway 

3. Target Range Road – Public Roadway (Commercial/Residential) 

Due to incomplete AADT datasets for this region, only an AADT for Target Range Rd could be 

identified (6468). No AADT data was available for Hohokam Dr and La Quinta Rd. Since these 

roadways were commercial/industrial roadways, AADT could not be estimated in the same 
8

manner as the residential roadways. For these reasons, VMT was not calculated for Hohokam Dr. 

and La Quinta Rd. VMT calculation for Target Range Road can be accomplished by multiplying 

AADT by road segment length (0.2 miles) resulting in a VMT of 1294. 

In order to calculate total PM10 emissions from unpaved roadways, ADEQ calculated unpaved 

road emission factors for a range of possible surface material silt contents within the Nogales NA 

using equations 1(b) and 2 from EPA AP-42 5th Ed. Volume 1 Chapter 13.2.2. A low surface 

material silt content value of 2.90% and a high surface material silt content value of 7.50% were 

utilized per EPA recommendation and based on the Mexican NEI (2004) and the Mexicali 

Emission Inventory (2005). These calculations are shown below: 

   

  C

M

Ss k

E c

a d

 

5.0

3012

Where: 

E = PM10 emission factor (lb/VMT) = 0.248 lb/VMT (low value) & 0.642 lb/VMT (high 

value)

k = Empirical Constant = 1.8 lb/VMT (EPA AP-42 Chapter 13.2.2, 2006) 

s = surface material silt content (%) = 2.90 % and 7.50 % (recommended by EPA and based on 

the Mexican NEI – 2004 and the Mexicali Emission Inventory - 2005). 

M = surface material moisture content (%) = 5.23 % (No reliable surface soil moisture 

measurements are known for the area. Therefore, the average 2 inch depth soil moisture from 

Walnut Gulch, AZ NRCS Site # 2026 for the year of 2008 of 4.30% was adjusted for Nogales, 

AZ based on the average annual difference in rainfall between the two locations of 21.5% 

[Balling, 1988]) 

S = mean vehicle speed (mph) = 25 mph (Based on the typical unpaved road speed limit in 

Arizona) 

a = Empirical Constant = 1 (EPA AP-42 Chapter 13.2.2, 2006) 

c = Empirical Constant = 0.2 (EPA AP-42 Chapter 13.2.2, 2006) 

d = Empirical Constant = 0.5 (EPA AP-42 Chapter 13.2.2, 2006) 

C = 0.00047 lb/VMT (EPA AP-42 Chapter 13.2.2, 2006) 

This emission factor was then corrected to only account for non-rainy days: 

est      PEE 365/365

Where: 

Eest = annual size-specific emission factor extrapolated for natural mitigation (lb/VMT) = 

0.217 lb/VMT (low value) & 0.563 lb/VMT (high value) 

E = the unadjusted emission factor = 0.248 lb/VMT (low value) & 0.642 lb/VMT (high value) 

P = number of days in a year with at least 0.254 mm (0.01 in) of precipitation = 45 days (EPA 

AP-42 Figure 13.2.2-1., 2006) 
9

Using the above calculated emission factors of 0.217 lb/VMT and 0.563 lb/VMT, and the total 

VMT of 278,655 miles for public, chip sealed roadways in the Nogales, ADEQ calculated total 

emissions from unpaved roadways to be: 

EVMTE   miles  VMTlb   tonlb  Low EST   /2000//217.0*655,7822000/* = 30.2 tons

EVMTE   miles  VMTlb   tonlb  High EST  2000/*  /2000//563.0* 278,655 = 78.4 tons

Therefore, the total PM10 emissions from public, chip sealed roadways in Nogales prior to paving 

are estimated to be between 30.2 and 78.4 tons. 

A double layer of chip-seal was applied to those Nogales roadways listed in Table E.5. This type 

of paving has been estimated as having a control efficiency of approximately 90% if it is 

combined with paved shoulders, curbs and gutters (Engineering Science, 1987). In order to 

determine the PM10 emission reductions observed from the chip-sealing of the roadways 

previously mentioned, two separate methods of calculating emissions from chip sealed roadways 

are presented below. The two emission estimates differ in the control efficiency utilized for the 

chip-sealing with: Method 1) utilizing 90% control efficiency for chip-sealed areas and Method 

2) utilizing a paved road emission factor for the chip-sealed areas where the paved road emission 

factor was calculated by utilizing Eq. 2 from AP 42: 13.2.1-5 (EPA, 2011). 

METHOD 1 (M1) 

Method 1 utilized 90% control efficiency for those roadways which have been chip-sealed. Table 

E.7 presents the calculated emissions from these roadways assuming no control measures were 

utilized (30.2 tons/yr PM10 emitted when utilizing EEST-Low and 78.4 tons/yr PM10 emitted when 

utilizing EEST-High) and assuming all roadways were chip-sealed resulting in 90% control 

efficiency (3.02 tons/yr PM10 emitted when utilizing EEST-Low and 7.84 tons/yr PM10 emitted when 

utilizing EEST-High). 

Table E.7 

Calculated PM10 Emissions Assuming 90% Chip-Seal Efficiency 

Roadway VMT 

Unpaved 

Emissions, 

Low [tons] 

Unpaved 

Emissions, 

High [tons] 

Chip-sealed 

Emissions, 

Low [tons] 

Chip-sealed 

Emissions, 

High [tons] 

Royal Rd 16178 1.76 4.55 0.176 0.455 

Vista del Cielo 160072 17.37 45.06 1.737 4.506 

Yucca Drive S. 13696 1.49 3.86 0.149 0.386 

Bristol Dr 7875 0.85 2.22 0.085 0.222 

Frank Reed Rd 62616 6.79 17.63 0.679 1.763 

Kino Rd 3835 0.42 1.08 0.042 0.108 

Kelsey Rd 6240 0.68 1.76 0.068 0.176 

West 1st St 6848 0.74 1.93 0.074 0.193 

Target Range Rd 1294 0.14 0.36 0.014 0.036 

Total 278655 30.2 78.4 3.02 7.84 
10

METHOD 2 (M2)

Method 2 assumed double chip-sealed roadways would produce emission reductions to the same 

degree as asphalt paved roadways. Therefore, an emission factor was calculated for the paved 

roadways using Eq. 2 from AP 42: 13.2.1-5 (EPA, 2011). This calculation is shown below: 

       N WsLkE P

4 1 91.0 02.1



Where: 

E = annual average emission factor = 0.000841 lbs/VMT 

k = particle size multiplier for particle size range and units of interest = 0.0022 lbs/VMT (Table 

13.2.1-1. from AP-42, EPA 2011) 

sL = road surface silt loading = 0.105 g/m2

 (Assumed to be comparable to an average silt loading 

value measured from local traffic roads in Table 3, page 28 of Phoenix Airshed Particulate 

Emissions study, Arizona State University 2006) 

W = average weight of the vehicles traveling the road = 3 tons (Arizona State University 2006, 

pg. 27) 

P = number of "wet" days with at least 0.254 mm (0.01 in) of precipitation during the averaging 

period = 45 days (EPA AP-42 Figure 13.2.2-1., 2006) 

N = number of days in the averaging period = 365 days 

The calculated emission factor does not account for brake wear and tire wear emissions and thus, 

EPA’s Motor Vehicle Emission Simulator (EPA MOVES2010a, 2009) was run for the year of 

2008 for Santa Cruz County in order to estimate an emission factor for these processes at the 

county level. This emission factor was then added to the paved roadway emission factor above 

(0.000841 lbs/VMT). MOVES calculated an emission factor of 0.000220 lbs/VMT. When the 2 

emission factors are summed a total emission factor of 0.00106 lbs/VMT is calculated for paved 

roads in the Nogales NA. 

Table E.8 presents the emissions from these roadways assuming no control measures were 

utilized (30.2 tons/yr PM10 emitted when utilizing EEST-Low and 78.4 tons/yr PM10 emitted when 

utilizing EEST-High) and assuming all roadways were chip-sealed with a paved road emission factor 

of 0.00106 lbs/VMT (0.148 tons/yr PM10 emitted when utilizing EEST-Low and EEST-High). 
11

Table E.8 

Calculated PM10 Emissions Assuming Paved Road Efficiency 

Roadway VMT 

Unpaved 

Emissions, 

Low [tons] 

Unpaved 

Emissions, 

High [tons]

Paved Road 

Emissions 

[tons] 

Royal Rd 16178 1.76 4.55 0.0086 

Vista del Cielo 160072 17.37 45.06 0.0848 

Yucca Drive S. 13696 1.49 3.86 0.0073 

Bristol Dr 7875 0.85 2.22 0.0042 

Frank Reed Rd 62616 6.79 17.63 0.0332 

Kino Rd 3835 0.42 1.08 0.0020 

Kelsey Rd 6240 0.68 1.76 0.0033 

West 1st St 6848 0.74 1.93 0.0036 

Target Range Rd 1294 0.14 0.36 0.0007 

Total 278655 30.2 78.4 0.148 

From the results calculated in Methods 1 and 2 (Tables E.7 & E.8). We can assume that the 

application of chip-sealing to the 9 roadways listed resulted in the reduction in PM10 emissions 

between 27.2 and 30.1 tons per year assuming low unpaved road silt content (2.90 %) and 70.6 

and 78.3 tons per year assuming a high unpaved road silt content (7.50 %). Conservatively, we 

can assume that chip-sealing the roadways reduced PM10 emissions within Nogales, AZ by 27.2 

tons per year. 

Results

This Technical Support Document (TSD) presents control measures for the Nogales NA which 

are already implemented and calculates the resultant PM10 emission reductions of these measures. 

Between 1992 and 2008, 17.0 combined miles of roadway were chip sealed in the Rio Rico and 

Nogales portions of the Nogales NA. In this TSD, ADEQ presented 2 methods of calculating 

emission reductions for these chip sealed roadways, whereby emission reductions were calculated 

by: Method 1) Assuming chip sealing provides 90% control efficiency of emissions and Method 

2) assuming chip sealing provides emissions rates equivalent to paving the roadways. 

Furthermore, emission rates were calculated for a range of surface silt contents between 2.9 % 

and 7.5 % to account for unknown and variable soil silt contents within the region. These 

calculations resulted in a range of PM10 emissions reductions for the Nogales NA (i.e. a 

combination of Rio Rico and Nogales emission reductions) of 64.5 - 71.3 tons/year assuming low 

surface soil silt content and 167 – 185 tons/year assuming high surface soil silt content for those 

areas surrounding the 14 chip sealed roadways identified in this study. Therefore, a conservative 

estimate of the emission reductions within the Nogales NA, due to chip sealing of these 

roadways, would be 64.5 tons/year. 
12

REFERENCES

“2005 Mexicali Emissions Inventory”, Final Report, February 27, 2009, Eastern Research Group, 

Inc. (ERG). 

Arizona State University (ASU), 2006. A FIELD STUDY OF PARTICULATE EMISSIONS 

FOR MAJOR ROADWAYS IN THE PHOENIX AIRSHED Final Report 495. 

Balling, R.C. 1988. The climatic impact of a Sonoran vegetation discontinuity. Climatic Change. 

13(1): 99-109. 

Engineering-Science. 1987. PM10 Emissions Inventory Data for the Douglas Planning Area. EPA 

Contract No. 68-02-3888. 

“Mexico National Emissions Inventory, 1999: Six Northern States”, Final, April 30, 2004, 

prepared by Eastern Research Group (ERG), Acosta Y Asociados, and Transengineering, for the 

Secretariat of the Environment and Natural Resources and the National Institute of Ecology of 

Mexico, the United States Environmental Protection Agency, the Western 

Governors’Association, and the North American Commission for Environmental Cooperation. 

(1999 Mexico NEI). 

National Resource Conservation Service (NRCS), USDA. 

http://www.wcc.nrcs.usda.gov/nwcc/site?sitenum=2026&state=az. Site # 2026. 

U.S. Department of Transportation, 2011. Summary of Travel Trends: 2009 National Household 

Travel Survey. http://nhts.ornl.gov/2009/pub/stt.pdf. 

U.S. EPA., 1995. Compilation of air pollutant emission factors, Volume 1. AP 42, Fifth Edition, 

http://www.epa.gov/ttn/chief/ap42/index.html#toc. 

U.S. EPA., 2009. Motor Vehicle Emission Simulator (MOVES) 2010 User Guide. EPA-420-B09-041. http://www.epa.gov/otaq/models/moves/420b09041.pdf. 

USGS. Binational Digital Soils Map of the Ambos Nogales Watershed, Southern Arizona and 

Northern Sonora, Mexico. Open-File Report 2004-1335. 
Appendix E.1 

Vehicle Miles Traveled Calculation 

This appendix includes information used to calculate the emission reductions from double chipsealing in the technical support document (TSD). ADEQ estimated the number of vehicle miles 

travelled (VMT) for roads in the Rio Rico portion of the Nogales NA with data provided by the 

following sources: 

 double chip-sealed road lengths provided by Santa Cruz County 

 the number of dwellings traveling on applicable paved roads was verified with aerial imagery 

 the average number of trips per household per year was based on household income data 

for Rio Rico obtained from the 2010 U.S. Census 
This page is intentionally blank. 
13

Appendix E.1: VMT Calculation

Table A.1: This table presents individual roadway length, the number of houses observed on the 

roadway, and the average number of trips taken per household for the Rio Rico area of the 

Nogales NA. VMT is calculated by the product of these values multiplied by an adjustment ratio 

of 0.5 (average distance of each roadway travelled by residents) and divided by 5280 (conversion 

from feet to miles). 

Roadway Length (L) [ft] Houses (H) Trips/household (T) VMT

Paseo Guebabi 14278 63 1981 168746

Paseo Mexico 21298 49 1981 195774

Calle Coyote 9008 38 1981 64217

River Rd 54910 31 1981 319323

Calle Arikara 5761 21 1981 22694

Circulo Tumbleweed 4442 15 1981 12500

Via Aloe Vera 4682 14 1981 12296

Camino Estrella 4891 13 1981 11928

Calle Cumpas 3587 11 1981 7402

Ceiba Ct 541 9 1981 913

Tala Ct 893 9 1981 1508

Ameca Ct 2817 8 1981 4228

Circulo Montana 24939 8 1981 37428

Circulo Mendez 1434 7 1981 1883

Annette Ct 1113 7 1981 1461

Gigi Ct 299 6 1981 336

Via Tecoripa 2115 6 1981 2380

Camino Estrella 4891 6 1981 5505

Campo Rd 1459 6 1981 1642

Padilla Ln 1128 6 1981 1270

Calle Ranuculo 2545 5 1981 2387

Cocula Ct 838 5 1981 786

Colmenar Ct 460 5 1981 432

Grillo Ct 475 5 1981 445

Batuc Ct 1131 5 1981 1061

Paseo Matamoros 7740 5 1981 7260

Calle Tepache 1089 5 1981 1021

Tuly Ct 264 5 1981 248

Corralitos Ln 906 5 1981 849

Via Dedal 1035 4 1981 776

Guaymas Ct 1360 4 1981 1021

Moneda Ct 212 4 1981 159

Lisboa Ct 820 4 1981 615

Cobra Ct 680 4 1981 510

Estoque Ct 818 4 1981 614

Forja Ct 532 4 1981 399

Camino Brizza Bonell 10183 4 1981 7641

Calle Cumpas 3587 4 1981 2692

Bacanora Ct 984 3 1981 554

Calle Remedios 6110 3 1981 3438

Corinto Ct 4176 3 1981 2350
14

Roadway Length (L) [ft] Houses (H) Trips/household (T) VMT

Llama Ct 408 3 1981 230

Via Italia 1042 3 1981 586

Arizpe Ct 259 3 1981 146

Meteoro Ct 228 3 1981 128

Cohete Ct 201 3 1981 113

Via Rita 1130 3 1981 636

Managua Ct 1893 3 1981 1065

Paseo Montura 2048 3 1981 1152

Fuego Ct 231 3 1981 130

Toltec Ct 284 2 1981 106

Beso Ct 212 2 1981 79

Boar Ln 391 2 1981 147

Copa Ct 356 2 1981 134

Suma Ct 101 2 1981 38

Uni Ln 261 2 1981 98

Soltar Ct 335 2 1981 126

Camino Loma 630 2 1981 236

Dosel Ct 580 2 1981 218

Toto Ct 202 2 1981 76

Adelita Ct 2271 2 1981 852

Payaso Ct 637 2 1981 239

Paseo Molango 4056 2 1981 1522

Trinity Ct 1458 2 1981 547

Hazel Ln 646 2 1981 242

Sunny Ln 685 2 1981 257

Via Papantla 2738 2 1981 1027

Via Pantera 2341 2 1981 878

Comoro Canyon Ln 2668 2 1981 1001

Kachina Dr 5498 2 1981 2063

Calle Coco 7706 2 1981 2891

Nikos Way 1846 2 1981 692

Via Fray Marcos 3932 1 1981 738

Calle Jamaica 4895 1 1981 918

Abanico Ct 451 1 1981 85

Inca Ct 349 1 1981 65

Avenida Reynosa 1624 1 1981 305

Calle Mora 2735 1 1981 513

Lost Ct 71 1 1981 13

Tata Ct 339 1 1981 64

Nutria Ct 635 1 1981 119

Silo Ln 306 1 1981 57

Song Dog Ct 171 1 1981 32

Johnson Ct 363 1 1981 68

Kite Ln 303 1 1981 57

Oro Ct 340 1 1981 64

Cuello Ct 298 1 1981 56

Dedo Ct 346 1 1981 65
15

Roadway Length (L) [ft] Houses (H) Trips/household (T) VMT

Donna Ct 350 1 1981 66

Ures Ct 557 1 1981 105

Zeus Ln 366 1 1981 69

Avenida Talanga 2515 1 1981 472

Jar Ct 77 1 1981 14

Tizimin Ct 2376 1 1981 446

Misa Ct 264 1 1981 49

Dandelion Ln 753 1 1981 141

Heno Ct 580 1 1981 109

Laguna Ct 403 1 1981 76

Mano Ct 286 1 1981 54

Purisima Ct 930 1 1981 174

Mia Ct 173 1 1981 33

Globo Ct 224 1 1981 42

Spices Ln 175 1 1981 33

Avenida Reynosa 1624 1 1981 305

Managua Ct 1893 1 1981 355

Paseo Matamoros 7740 1 1981 1452

Paseo Sombrilla 1666 1 1981 313

Mt Benedict Dr 1544 1 1981 290

Compostela Ct 724 1 1981 136

Gunsight Rd 4470 1 1981 838

Camino Vista Sonora 9721 1 1981 1824

Calle Jamaica 4895 1 1981 918

Duquesne Rd 160673 1 1981 30141

Amura Ln 2329 1 1981 437

Tree Ln 675 0 1981 0

Bola Ct 281 0 1981 0

Cacao Ct 398 0 1981 0

Belice Ct 256 0 1981 0

Cha Ct 173 0 1981 0

Adios Ct 256 0 1981 0

Paseo Sombrilla 1666 0 1981 0

Rum Ln 301 0 1981 0

Sahuarita Ct 1941 0 1981 0

Sana Ct 364 0 1981 0

Toluca Ct 1310 0 1981 0

Zaragoza Ct 1669 0 1981 0

Sodio Ct 259 0 1981 0

Acuna Ct 1363 0 1981 0

Del Ct 84 0 1981 0

Mescal Ct 820 0 1981 0

Compostela Ct 724 0 1981 0

Lazo Ct 366 0 1981 0

Leek Ct 137 0 1981 0

Luz Ct 325 0 1981 0

Maidu Ct 662 0 1981 0
16

Roadway Length (L) [ft] Houses (H) Trips/household (T) VMT

Marcarla Ct 1091 0 1981 0

Odisea Ct 594 0 1981 0

Salama Ct 1974 0 1981 0

Sauzal Ct 916 0 1981 0

Yard Ln 380 0 1981 0

Yuma Ct 110 0 1981 0

Calle Barril 2967 0 1981 0

Calle Granja 631 0 1981 0

Camino Cumbre 5343 0 1981 0

Camino Real 6824 0 1981 0

Fino Ct 1652 0 1981 0

Roble Ct 578 0 1981 0

Rosas Ct 450 0 1981 0

Calle Torreon 2888 0 1981 0

Nina Ct 228 0 1981 0

Circulo Huacana 2332 0 1981 0

Codo Ct 367 0 1981 0

Cola Ct 251 0 1981 0

Cono Ct 220 0 1981 0

Dividir Ct 2570 0 1981 0

Rey Ct 187 0 1981 0

Stable Ln 1072 0 1981 0

Tiarra Ct 230 0 1981 0

Calle Chivato 1171 0 1981 0

Cara Ct 312 0 1981 0

Hebilla Ct 921 0 1981 0

Kay Ct 1171 0 1981 0

Loreto Ct 723 0 1981 0

Tambor Ct 435 0 1981 0

Trono Ct 860 0 1981 0

Vereda Guadalajara 3286 0 1981 0

Paseo Montura 2048 0 1981 0

Tizimin Ct 2376 0 1981 0

Paseo Matamoros 7740 0 1981 0

Calle Cenote 990 0 1981 0

Stable Ln 1072 0 1981 0

Sonoita Creek Ranch Rd 15849 0 1981 0

Guajolote Ct 749 0 1981 0

Stoddard Way 5333 0 1981 0

Poppy Ct 4176 0 1981 0

Bodega Dr 1580 0 1981 0

Calle Barril 2967 0 1981 0

Calle Mandarina 6170 0 1981 0

Placita Verdura 907 0 1981 0

Garra Ct 350 0 1981 0

Wild Rose Ct 834 0 1981 0

Victorio Dr 3477 0 1981 0
17

Roadway Length (L) [ft] Houses (H) Trips/household (T) VMT

Pendleton Dr 76784 0 1981 0

Corinto Ct 4176 0 1981 0

Camino Real 6824 0 1981 0

Trono Ct 860 0 1981 0

Zaragoza Ct 1669 0 1981 0

Camino Las Barrancas 3102 0 1981 0

Camino Real 6824 0 1981 0

Calle Torreon 2888 0 1981 0

Paseo Riachuelo 6524 0 1981 0

Paseo Riachuelo 6524 0 1981 0

Circ Vista Del Lago 5022 0 1981 0

Circ Vista Del Lago 5022 0 1981 0

Cuates Buttes Ln 4020 0 1981 0

Del Rey David Blvd 5986 0 1981 0

Bravo Ln 1379 0 1981 0

 Total VMT 968460

 Total PM10 (ELow) 105

 Total PM10 (EHigh) 273
This page is intentionally blank. 
Appendix E.2 

Road Paving/Chip-Sealing Documentation Provided by Santa Cruz County 

for the Nogales NA 

The documents in this appendix were provided by Santa Cruz County. County officials 

highlighted roads that had been double chip-sealed in the Rio Rico community from 

2002-2008. ADEQ determined four roads totaling 8.6 miles were within the Nogales NA. 

This information was then used for the calculations in the technical support document. 
This page is intentionally blank. 





This page is intentionally blank. 
Appendix E.3 

ADEQ Map Displaying Paved and Unpaved Roads in the Rio Rico 

Section of the Nogales NA 

This appendix contains a map developed by ADEQ using geographic information system (GIS) 

data to show which roads in the Nogales NA, excluding the City of Nogales, were paved and 

unpaved. ADEQ determined 134.4 miles of road were paved and 53.5 were unpaved in this 

section of the Nogales NA. 
This page is intentionally blank. 

This page is intentionally blank. 
Appendix E.4 

Satellite Imagery used to Verify Road Paving/Double Chip-Sealing in the Nogales NA 

This appendix contains before and after satellite imagery for each paved road cited in the TSD. 

The black and white 1992 images are blurry, typical of satellite imagery from that era, and 

somewhat difficult to discern. Some roads identified for paving in the 1993 Nogales NA SIP 

appear to have been paved when the 1992 satellite image was taken, likely due the development 

process for the 1993 Nogales NA SIP taking several years to complete. Satellite imagery is 

unavailable for years prior to 1992. 
This page is intentionally blank. 
Figure 1: Aerial photography of Calle Arikara road in Rio Rico from 1992 (left) and 2010 (right) confirming chi

roadway occurred between these dates. 
Figure 2: Aerial photography of Paseo Mexico road in Rio Rico from 1992 (top) and 2010 (bottom) confirming 

the roadway occurred between these dates. 
Figure 3: Aerial photography of Calle Coyote road in Rio Rico from 1992 (left) and 

2010 (right) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 4: Aerial photography of Annette Ct. in Rio Rico from 1992 (left) and 2010 (right) confirming chip-seal p

occurred between these dates. 
Figure 5: Aerial photography of Paseo Guebabi road in Rio Rico from 1992 (top) and 

2010 (bottom) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 6: Aerial photography of Royal Road in Nogales from 1992 (left) and 2010 

(right) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 7: Aerial photography of Hohokam Road in Nogales from 1992 (left) and 2010 

(right) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 8: Aerial photography of La Quinta Road in Nogales from 1992 (top) and 2010 (bottom) confirming chip

roadway occurred between these dates. 
Figure 9: Aerial photography of Yucca Dr. in Nogales from 1992 (top) and 2010 

(bottom) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 10: Aerial photography of Bristol Dr. in Nogales from 1992 (top) and 2010 (bottom) confirming chip-sea

roadway occurred between these dates. 
Figure 11: Aerial photography of Target Range Rd. in Nogales from 1992 (top) and 2010 

(bottom) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 12: Aerial photography of Frank Reed Rd. in Nogales from 1992 (top) and 2010 

(bottom) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 13: Aerial photography of Kino Rd. in Nogales from 1992 (top) and 2010 (bottom) confirming chip-seal 

roadway occurred between these dates. 
Figure 14: Aerial photography of Kelsey Ave. in Nogales from 1992 (top) and 2010 

(bottom) confirming chip-seal paving of the roadway occurred between these dates. 
Figure 15: Aerial photography of W 1st Ave. in Nogales from 1992 (top) and 2010 (bottom) confirming chip-se

roadway occurred between these dates. 
Figure 16: Aerial photography of Vista del Cielo - the main collector shown in the photographs 

below - in Nogales from 1992 (top) and 2012 (Bing Maps) confirming paving of the roadway 

occurred between these dates. 
Appendix F 

Correspondence
This page is intentionally blank. 
Appendix F.1 

Letter from EPA Approving Arizona's Air Monitoring Network Plan for 2011
This page is intentionally blank. 


Appendix F.2 

Email from Santa Cruz County Confirming Road 

Maintenance Procedures and Equipment
This page is intentionally blank. 
James Wagner

From: Carlos Rivera [crivera@co.santa-cruz.az.us]

Sent: Monday, April 02, 2012 5:39 PM

To: James Wagner

Subject: FW: Nogales PM10 Nonattainment Area 

Attachments: PM10 Non attainment area map.pdf

Page 1 of 1

4/6/2012

Mr. Wagner,

Attached and below is the response from our Public Works Director. If you should require any additional

information please do not hesitate to contact me.

Carlos

From: Jesus J. Valdez 

Sent: Monday, April 02, 2012 4:09 PM 

To: Carlos Rivera 

Subject: RE: Nogales PM10 Nonattainment Area 

 

Carlos,

Attached is a map of the nonattainment area.  The County has a total of 240 miles of roads: 40 miles of

dirt roads & 200 miles of paved/double chip roads.

In addition, the County has implemented an on‐call program that has PW employees on standby after

regular working hours to respond to road emergencies and/or road blockage. PW crews also do clean up

after every storm event by removing debris and sweeping the road. The PW department currently has

two sweepers in the heavy equipment fleet.  

Jesus Valdez, P.E.

Interim Public Works Director

County Engineer

Santa Cruz County

Ph.   520‐375‐7830

Fax. 520‐375‐7846

Appendix F.3 

Email from City of Nogales Confirming Road Paving, Road 

 Maintenance Procedures and Equipment 
This page is intentionally blank. 
From: Juan Guerra [mailto:jguerra@nogalesaz.gov] 

Sent: Wednesday, April 11, 2012 3:24 PM 

To: James Wagner 

Cc: edelgado@nogalesaz.gov; abarcenas@nogalesaz.gov 

Subject: Re: Nogales Street Sweepers

We are working on it to get the total length of paved roads. Although all public roads are paved some of

them require significant improvements.  

As you may be aware, there are some private roads and commercial properties not paved.

 

From: James Wagner [mailto:Wagner.James@azdeq.gov] 

Sent: Wednesday, April 11, 2012 12:19 PM 

To: Juan Guerra <jguerra@nogalesaz.gov> 

Subject: FW: Nogales Street Sweepers 

 

Hello again, Juan. 

EPA would like us to get data layers for paved/unpaved roads in Nogales so that we can claim emissions 

reductions for unpaved roads identified in the 1987 emissions inventory for the Nogales area. Can you 

help us with that request?

Thanks,

Jim Wagner

EHS II

602.771.2388

 

From: Juan Guerra [mailto:jguerra@nogalesaz.gov] 

Sent: Thursday, December 08, 2011 3:42 PM 

To: James Wagner 

Cc: Tony Santa Cruz 

Subject: RE: Nogales State Implementation Plan 

 

Hi Jim:

Please see below the answers to your questions. Let me know if you have any more questions.

1.‐ The City has two sweeper but only one is in operation (The other is broken).

2.‐The two street sweepers are standard.

3.‐The streets are cleaned from Monday‐Friday (No weekends and holydays)

4.‐The City does not block any private unpaved road.

Sincerely,

Juan Guerra, PE., CFM| City Engineer | City of Nogales, AZ | phone: 520‐285‐5753| fax: 520‐287‐8352 |

1450 N. Hohokam Drive, Nogales, AZ 85621 | jguerra@nogalesaz.gov

Office hours: Monday – Friday, 8 a.m. – 5 p.m.

E‐mails generated by council members, members of City commissions and committees or by staff and that pertain to City

business are public records. Therefore, the e‐mails must be preserved according to the City’s records retention schedule and
generally be made available for public inspection. E‐mail correspondence is regularly reviewed by members of the public and

other interested parties, including media outlets and reporters. To ensure compliance with the Open Meeting Law, members of

the City Council, and of City commissions and committees should not forward e‐mail correspondence to other members of the

Council, board or commission. Members of the Council and other public bodies may reply to this message, but should not copy

other members of the public body. Any questions should be directed to the City of Nogales' City Attorney: (520) 287‐6571.

From: James Wagner [mailto:Wagner.James@azdeq.gov] 

Sent: Thursday, December 08, 2011 3:22 PM 

To: Juan Guerra 

Subject: Nogales State Implementation Plan 

 

Hello Juan, 

It was nice speaking with you earlier. We just need to know a few things for the update to the 

1993 Nogales PM10 state implementation plan. 

 How many street sweepers does the City own? 

 Are they "PM10 certified" or standard sweepers? 

 How often does the City clean the streets? 

For those unpaved roads not accepted into the City's Street Maintenance Program, does the City 

try to block traffic, for example with boulders? 

If you have any questions, please let me know. 

Thanks, 

Jim Wagner 

ADEQ Air Quality Division

602.771.2388 

NOTICE: This e-mail (and any attachments) may contain PRIVILEGED OR CONFIDENTIAL information and is intended only 

for the use of the specific individual(s) to whom it is addressed. It may contain information that is privileged and 

confidential under state and federal law. This information may be used or disclosed only in accordance with law, and you 

may be subject to penalties under law for improper use or further disclosure of the information in this e-mail and its 

attachments. If you have received this e-mail in error, please immediately notify the person named above by reply e-mail, 

and then delete the original e-mail. Thank you.

NOTICE: This e-mail (and any attachments) may contain PRIVILEGED OR CONFIDENTIAL information and is intended only 

for the use of the specific individual(s) to whom it is addressed. It may contain information that is privileged and 

confidential under state and federal law. This information may be used or disclosed only in accordance with law, and you 

may be subject to penalties under law for improper use or further disclosure of the information in this e-mail and its 

attachments. If you have received this e-mail in error, please immediately notify the person named above by reply e-mail, 

and then delete the original e-mail. Thank you.
Appendix F.4 

Completeness Letter from EPA for the 1993 Nogales PM10 Nonattainment Area 

State Implementation Plan 
This page is intentionally blank. 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION IX 

75 Hawtharne Street 

San Francisco, Ca. 94105 

November 30, 1993 

Edward Z. Fox 

Director 

Arizona Department of Environmental - Quality 

3033 North Central Avenue 

Phoenix, Arizona 85012 

Dear Mr. Fox: 

On June 14,1993, you submitted a revision to the Arizona State Implementation Plan 

for achieving and maintaining the National Ambient Air Quality Standards for particulate 

matter 10 microns or less in aerodynamic diameter (PM10) in the Nogales nonattainment 

area. 

We have revikwed this package for completeness and found that it conforms to the 

completeness criteria in 40 CFR Part 5 1, Appendix V. The complete submittal addresses 

the finding of nonsubmittal made by EPA on December 16, 1991, and thus stops the clock 

for mandatory sanctions under section 179(a) of the Clean Air Act. 

The SIP revision found to be complete is now in the process of being reviewed. 

Once reviewed, we will prepare a rulemaking notice for submittal to our Headquarters 

office for publication in the Federal Register. 

If you have any questions regarding our review, please call me or have your staff call 

Wallace Woo, Chief of the Plans Development Section in the Air Planning Branch at 

(4 15)744- 1207. 

Sincerely, 

David P. Howekamp 

Director 

Air & Toxics Division 

cc: Nancy Wrona, Arizona Department 

of Environmental Quality 

Printed on Recycled Paper 
This page is intentionally blank. 
Appendix F.5 

Santa Cruz County Email Regarding Paved Roads in Rio Rico 
This page is intentionally blank. 
From: Jesus J. Valdez [mailto:jjvaldez@co.santa-cruz.az.us] 

Sent: Thursday, March 03, 2011 5:57 PM 

To: Roxanne J. Linsley 

Subject: FW: highlighted roads!

Attached is a pdf of the dirt roads that the County has chip seal since 2002, its roughly about 60 miles.  From oral

history, staff informed me that an additional 40 miles of dirt roads were chip seal from 1993 to 2001. Also, I

research for a policy that the County had adopted regarding clean up after storm events, and was unsuccessful in

finding one.  Please give me a call if you have any questions.   

Jesus Valdez, P.E.

Interim Public Works Director

County Engineer

Santa Cruz County

Ph.   520‐375‐7830

Fax. 520‐375‐7846

From: Norma Northcross 

Sent: Thursday, March 03, 2011 5:44 PM 

To: Jesus J. Valdez 

Subject: highlighted roads! 

Thanks
NORMA B. NORTHCROSS

Central Permits Coordinator

Right of Way Agent

Santa Cruz County

(520) 375-7869

 

NOTICE: This e-mail (and any attachments) may contain PRIVILEGED OR CONFIDENTIAL 

information and is intended only for the use of the specific individual(s) to whom it is addressed. 

It may contain information that is privileged and confidential under state and federal law. This 

information may be used or disclosed only in accordance with law, and you may be subject to 

penalties under law for improper use or further disclosure of the information in this e-mail and its 

attachments. If you have received this e-mail in error, please immediately notify the person 

named above by reply e-mail, and then delete the original e-mail. Thank you. 
1

APPENDIX G 

SUPPLEMENTARY INFORMATION 

 The information included in this appendix is considered supplementary and not included for 

submittal with this SIP. 

1. Require Dust Control Plans for Construction or Land Clearing Projects 

 

Santa Cruz County Grading Ordinance 2001-06, adopted in 2001, was not included as a control 

measure in the 1993 Nogales SIP. The ordinance requires control measures for construction and land 

clearing projects. Permits are required for any grading activity exceeding 50 cubic yards. The grading 

ordinance requires dust control for all areas disturbed during grading or clearing of land.1

 The ordinance 

specifies that only land that will later be resurfaced, hydroseeded, landscaped, or developed may be 

disturbed. The ordinance further requires disturbed areas that are not landscaped or developed be 

hydroseeded. Officials are authorized to conduct site inspections to determine the adequacy of dust and 

erosion control methods and may require mitigation measures. Dust and erosion control methods must be 

completed within (30) days of clearing, unless waived by the County. 

 The City of Nogales Development Standards Code does not provide specific mitigation measures 

for land clearing and construction activity. Article 8, Section 8-5-6, however, requires “land use to 

comply with State and federal regulations, and prohibits particulate emissions from creating public 

health concerns...No emission shall be permitted which can cause damage to health, to animals, or 

vegetation, or other forms of property...” These provisions provide local agencies with authority to 

pursue air quality nuisances, including emissions related to construction or land clearing projects.2

 

2. Provide for Storm Water Drainage to Prevent Water Erosion onto Paved Roads/ 

 Provide for Traffic Rerouting or Rapid Clean Up of Temporary Sources of Dust on 

 Paved Roads 

 Section 8-6-6 of the City of Nogales building code, Surface Drainage and Storm Sewer System, 

requires that building permits will only be issued after provisions to control storm water run-off, 

including culverts or inlets, have been implemented. These provisions prevent sediment from washing 

onto paved streets and creating vehicle trackout emissions. Section 8-6-6 also requires detention basins or 

other means of preventing significant water run-off where applicable. Section 8-16-23, Design Standards 

for On-Site Retention of Storm Water, requires on-site storm water retention for all developments one 

acre or larger unless the site is served by a storm sewer, channel, or natural drainage way approved by the 

City Engineer.3

 

 Santa Cruz County's Flood Control District established standards for private driveway crossings 

to prevent erosion onto paved roads.4

 

 

1

 Santa Cruz County Grading Ordinance 2001-06. Pgs. 6-7. 

<http://www.co.santa-cruz.az.us/com_development/building/pdf/GradingOrdinanceRevised.pdf> 2

 City of Nogales, Arizona, Development Standards Code, Article 8. Pgs. 66-67. 

<https://imageserv5.team-logic.com/mediaLibrary/78/Article_008.pdf> 

3

 Ibid. Pg. 167. 

4

 Santa Cruz Flood Control District. “Driveway Crossing Standards.” 

<http://www.co.santa-cruz.az.us/public_works/flood/pdf/DrivewayCrossingStandard.pdf> 
2

3. Require Curbing and Pave or Stabilize Paved Road Shoulders

 Section 8-8-2 of the Nogales City code requires that all “streets shall have Portland Cement 

Concrete curbs and gutters along the pavement edge constructed to city minimum standards for 

construction...All streets shall have Portland Cement Concrete sidewalks behind the curb-gutter where 

curb-gutter is required.”5

 

Section 1504.5, effective October 5, 1973, of the County Zoning and Development Code states 

that “...curbs and gutters shall be required in all Zoning Districts except GR (General Rural) and SR 

(Suburban Ranch) unless a variance is granted by the Planning Commission...”6

 Curbing streets and 

stabilizing road shoulders in the sparsely populated rural districts of Rio Rico is not currently 

economically feasible. 

4. Pave, Vegetate, or Chemically Stabilize Unpaved Parking Areas 

 Section 8-9-5 of the Nogales Development Standards Code, General Parking Lot Design 

Requirements, requires that “A. Surfacing and Drainage: Every commercial parking lot, including 

display areas for vehicle parking, shall be paved with two (2) inches of asphaltic concrete over four (4) 

inches of aggregate base course or four (4) inches of Portland Cement Concrete reinforced with #8 six 

(6) inch by six (6) inch wire mesh over a sub-base compacted to ninety-five percent (95%) density and 

properly drained with a minimum grade of 0.5% and a maximum grade of six percent (6%). Every 

commercial parking lot shall be subject to approval by the Site Plan process of Section 8-18.” 7 The code 

also requires the owner or occupant of a building with a paved parking area to maintain the surface, 

lighting, and landscaping or face a violation. 

 

 As required by the 1993 NNA SIP, the County paved the Sheriff’s station parking lot. In 2005, 

the County amended Article 11 of the County Zoning and Development Code to require paved parking 

lots and entrances for commercial buildings and multifamily residences.8

 

5. Pave, Vegetate, or Chemically Stabilize Unpaved Parking Areas 

 Section 8-9-5 of the Nogales Development Standards Code, General Parking Lot Design 

Requirements, requires that “A. Surfacing and Drainage: Every commercial parking lot, including 

display areas for vehicle parking, shall be paved with two (2) inches of asphaltic concrete over four (4) 

inches of aggregate base course or four (4) inches of Portland Cement Concrete reinforced with #8 six 

(6) inch by six (6) inch wire mesh over a sub-base compacted to ninety-five percent (95%) density and 

properly drained with a minimum grade of 0.5% and a maximum grade of six percent (6%). Every 

commercial parking lot shall be subject to approval by the Site Plan process of Section 8-18.” 9 The code 

 

5

 City of Nogales, Arizona, Development and Standards Code, Article 8. Pg. 89. 

<https://imageserv5.team-logic.com/mediaLibrary/78/Article_008.pdf> 

6

 Santa Cruz County Zoning and Development Code 2011. Pgs. 146-148. 

<http://www.co.santa-cruz.az.us/com_development/pdf/ZoningandDevelopmentCode.pdf> 7

 City of Nogales, Arizona, Development and Standards Code, Article 8. Pgs. 127-134. 

<https://imageserv5.team-logic.com/mediaLibrary/78/Article_008.pdf> 

8

 Santa Cruz County Zoning and Development Code 2011. Pg. 112. 

<http://www.co.santa-cruz.az.us/com_development/pdf/ZoningandDevelopmentCode.pdf>

9

 City of Nogales, Arizona, Development and Standards Code, Article 8. Pgs. 127-134. 

<https://imageserv5.team-logic.com/mediaLibrary/78/Article_008.pdf> 
3

also requires the owner or occupant of a building with a paved parking area to maintain the surface, 

lighting, and landscaping or face a violation. 

 As required by the 1993 NNA SIP, the County paved the Sheriff’s station parking lot. In 2005, 

the County amended Article 11 of the County Zoning and Development Code to require paved parking 

lots and entrances for commercial buildings and multifamily residences.10 

6. Require Revegetation, Chemical Stabilization, or other Abatement of Wind 

 Erodible Soil 

 The City of Nogales Development Standards Code does not provide specific mitigation measures 

for revegetation or stabilization of unstabilized soil; however, Article 8, Section 8-5-6 requires “land use 

to comply with State and federal regulations, and prohibits particulate emissions from creating public 

health concerns...No emission shall be permitted which can cause damage to health, to animals, or 

vegetation, or other forms of property...” These provisions give local authorities power to pursue air 

quality nuisances, including emissions related to construction or land clearing projects.11

 Santa Cruz County Ordinance 2001-06, Excavation and Grading, Section 3316-Erosion Control, 

requires that “Dust and erosion control shall be required for all areas disturbed during grading, clearing, 

or brushing of land whether it requires a grading permit or not. Only areas which will later be 

resurfaced, hydroseeded, landscaped, or built on may be disturbed. All disturbed areas which are not 

resurfaced, landscaped, or built on shall be hydroseeded with plant species appropriate to the site and its 

surrounding native habitat...The Building Official may make site inspections to determine the adequacy of 

dust and erosion control methods and may require modified mitigation measures, such as, but not limited 

to, paving, rip-rap, and, or, erosion control blankets. Dust and erosion methods shall be completed within 

(30) days of clearing, unless waived by the Building Official.”12

7. Road Paving in Nogales, Sonora, Mexico 

 The North American Development Bank (NADB) has funded road paving projects in Nogales, 

Sonora. A study of the city conducted from 2004-2007 determined that 65 percent of the city was 

unpaved, with 35 percent having some type of hard surface. According to the NADB, as of 2010, 865 

roads are surfaced. However, 1,065 roads extending 133 miles remained unpaved as of August 2010. In 

July 2004, the NADB announced 17 million U.S. in funding for street improvements.13 In 2007, the 

NADB announced 9 million U.S. dollar funding for street improvements.14 As of September 2011, the 

city was accepting bids on an additional 10 miles of road surfacing.15 More paving projects are planned 

for the immediate future. 

 

10 Santa Cruz County Zoning and Development Code 2011. Pg. 112. 

<http://www.co.santa-cruz.az.us/com_development/pdf/ZoningandDevelopmentCode.pdf> 11 City of Nogales, Arizona, Development Standards Code, Article 8. Pgs. 66-67. 

<https://imageserv5.team-logic.com/mediaLibrary/78/Article_008.pdf> 12 Santa Cruz County Grading and Excavating Ordinance. Pgs. 6-7. 

<http://www.co.santa-cruz.az.us/com_development/building/pdf/GradingOrdinanceRevised.pdf> 

13 North American Development Bank press release. July 2004. 

<http://www.nadb.org/pdfs/state_projects/FS%20Nogales%20SON%20AQ%20Eng.pdf> 14North American Development Bank press release. January, 2007. 

<http://www.nadb.org/Reports1/Press_Releases/english/2007/013007.htm>

15 
This page is intentionally blank. 
Appendix H 

NNA Monitoring Data 2008-2010
This page is intentionally blank. 
Appendix H 

Nogales Continuously Operating BAM Monitor 

Air Quality Data 2008-2010 

Year # of 

Observations 

% of 

Observations 

Max 24-hour 

Concentration 

(μg/m3)

2nd Highest 

Concentration 

(μg/m3)

# of 

Estimated 

Exceedances 

2008 355 97 234 217 13.2 

2009 343 94 238 204 2.0 

2010 126 35* 191 177 8.5 

3-Year Average Estimated Number of Exceedances 7.9 

*2010 data does not meet completeness criteria.

Appendix H 

Nogales Partisol Filter-Based Monitor 

Air Quality Data 2008-2010 

Year Quarter # of 

Observations 

% Data 

Completeness 

Max 24-hour 

Concentration 

(μg/m3)

2nd Highest 

Concentration 

(μg/m3)

# of 

Estimated 

Exceedances 

2008 1 15 88 108.7 99.7 

2 15 100 147.2 86.7 

3 15 100 44 41.3 

4 14 93 155.3 150.3 

 Annual 58 95 155.3 150.3 6.6 

2009 1 13 87 116.4 105.5 

2 16 100 57.9 51.8 

3 14 93 72.8 67.1 

4 15 100 123.8 109.7 

 Annual 58 95 123.8 116.4 0 

2010 1 15 100 96.8 84.7 

2 14 93 57.2 45.5 

3 15 94 63.3 55.9 

4 13 87 74.5 66.5 

 Annual 57 93 96.8 84.7 0 

3-Year Average Estimated Number of Exceedances 2.2 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

DESIGN VALUE REPORT

Report Request ID: 941451 Report Code: AMP480 Dec. 23, 2011

Selection Criteria Page 1

User ID: BNE

State County Site Parameter POC City AQCR UAR CBSA CSA

EPA

Region Method Duration Begin Date End Date

04 023 0004

GEOGRAPHIC SELECTIONS

PROTOCOL SELECTIONS

Parameter

Classification Parameter Method Duration

81102

SELECTED OPTIONS

USER SITE METADATA

MERGE PDF FILES

QUARTERLY DATA IN WORKFILE

WORKFILE DELIMITER

SINGLE EVENT PROCESSING

Option Type Option Value

STREET ADDRESS

YES

NO

,

EXCLUDE REGIONALLY CONCURRED EVENTS

GLOBAL DATES

2010

Start Date End Date

2010

Tribal

Code

APPLICABLE STANDARDS

Standard Description

PM10 24-hour 2006
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

AIR QUALITY SYSTEM

PRELIMINARY DESIGN VALUE REPORT

Report Date: Dec. 23, 2011

Notes:

1. Warning: Computed design values are a snapshot of the data at the time the report was run (may not be all data for year).

2. Annual Values not meeting completeness criteria are marked with an asterisk ('*').

Page 1 of 2
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

AIR QUALITY SYSTEM

PRELIMINARY DESIGN VALUE REPORT

Report Date: Dec. 23, 2011

Notes:

1. Warning: Computed design values are a snapshot of the data at the time the report was run (may not be all data for year).

2. Annual Values not meeting completeness criteria are marked with an asterisk ('*').

Page 2 of 2

Pollutant:

Standard Units:

NAAQS Standard:

Statistic:

PM10 Total 0-10um STP(81102) Design Value Year: 2010

Micrograms/cubic meter (25 C)(001)

PM10 24-hour 2006

Annual Estimated Days > Standard

REPORT EXCLUDES MEASUREMENTS WITH REGIONALLY CONCURRED EVENT FLAGS.

Level:150 State Name: Arizona

Site ID POC STREET ADDRESS

|

|

| Estimated

#Complete

Cert.

|

|

|Estimated

#Complete

Cert.

|

|

| Estimated Quarter Cert.

|

|

|

Estimated

Exceedances

Validity

Ind.

2010 2009 2008

04-023-0004

04-023-0004

1

3

300 N MORLEY AVE

300 N MORLEY AVE

 0

 8.5

4

0

 0

 2

4

4

 6.6

 13.2

4

4

 2.2

 7.9

Y

* Y

Count Quarter

Exceedances

0

6

Count Quarter

Exceedances

0

2

Count

Exceedances #Complete

1

13

3 - Year
Appendix I 

Quantitative Milestone and Reasonable Further Progress Report for the 

Nogales PM10 Nonattainment Area
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Appendix K 

Public Process Documentation 

This appendix contains the public process documents for the first and second public comment 

periods for the 2012 Nogales PM10 SIP: 

 

 Public Hearing Notice 

 Affidavit of Publication for Notice of Public Hearing 

 Hearing Agenda 

 Hearing Sign-in Sheet 

 Hearing Transcript 

 Public Comments 

 Responsiveness Summary 

 Public Hearing Offer 

 
This page is intentionally blank. 
ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY 

30 DAY PUBLIC COMMENT PERIOD AND HEARING ON 

NOGALES MODERATE PM10 MAINTENANCE PLAN 

The Arizona Department of Environmental Quality (ADEQ) is beginning a thirty day 

public comment period with the publication of this notice on May 18, 2012, for the 

proposed Nogales Moderate Area PM10 State Implementation Plan (SIP). The proposed 

SIP is an update of the plan submitted by ADEQ to the U.S. Environmental Protection 

Agency (EPA) for the Nogales Nonattainment Area (NNA) in 1993. 

A public hearing on the proposed SIP revision to be submitted to the U.S. Environmental 

Protection Agency the will be held on Thursday, June 21, 2012, at 2:00 p.m. at the 

Nogales Chamber of Commerce, 123 West Kino Park Place, Nogales, AZ 85621. All 

interested parties will be given an opportunity at the public hearing to submit relevant 

comments, data, and views, orally and in writing. Written comments may be submitted 

prior to or during the public hearing and must be postmarked or received by at ADEQ by 

5:00 p.m. on June 21, 2012. 

All written comments should be addressed, faxed, or e-mailed to: 

Jim Wagner 

Arizona Department of Environmental Quality - Air Quality Division 

1110 West Washington Street, Phoenix, AZ 85007 

FAX: (602) 771-2366 

E-Mail: JW3@azdeq.gov 

Copies of the PM10 SIP proposal are available for review online at the following web 

address http://www.azdeq.gov/cgi-bin/vertical.pl and in hard copy at the following 

locations: 

ADEQ Records Center 

First Floor, 1110 W. Washington Street 

Phoenix, Arizona 85007 

Attention: Norlene Lara, (602) 771-4712 

Nogales Library 

777 E. Grand Avenue 

Nogales, AZ 85621 

Attention: Suzanne Haddock, (520) 287- 6571 
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1

1 PROPOSED ARIZONA AIR QUALITY 

2 STATE IMPLEMENTATION PLAN (SIP) 

3 for the 

4 Nogales PM-10 Nonattainment Area 

5 

6 Oral Proceeding 

7 Hearing Officer Script 

8 2:00 PM, June 21, 2012 

9 

10 Bruce Friedl: Good afternoon and thank you for coming. I now open this hearing on a proposed 

11 revision to the Arizona State Implementation Plan for the 2012 Nogales PM-10 State 

12 Implementation Plan for the Nogales PM-10 Nonattainment Area. 

13 

14 It is June 21, 2012, and the time is 2:24 PM. The location is the Nogales-Santa Cruz County 

15 Chamber of Commerce, 123 West Kino Park Place, Nogales, AZ. My name is Bruce Friedl, and 

16 I have been appointed by the Director of the Arizona Department of Environmental Quality 

17 (ADEQ) to preside at this proceeding. 

18 

19 The purposes of this proceeding are to provide the public an opportunity to: 

20 (1) hear about the substance of the proposed air quality plan revision, 

21 (2) ask questions regarding the revision, and 

22 (3) present oral argument, data and views regarding the revision in the form of comments on the 

23 record. 

24 

25 Representing the Department is Diane Arnst. 

26 

27 Public notice appeared in the Nogales International on May 18 and 21, 2012, and on ADEQ’s 

28 website. The documents subject to comment were made available online at www.azdeq.gov and 

29 in hard copy at the ADEQ Phoenix office and at the Nogales-Rochlin Public Library at 518 N. 

30 Grand Ave. Nogales, AZ. 
2

1 The procedure for making a public comment on the record is straightforward. If you wish to 

2 comment, you need to fill out a speaker slip, which is available at the sign-in table, and give it to 

3 me. Using speaker slips allows everyone an opportunity to be heard and allows us to match the 

4 name on the official record with the comments. You may also submit written comments to me 

5 today. Please note, the comment period for the proposed SIP revision ends today, June 21, 2012 

6 at 5:00 PM. All comments must be postmarked or received at ADEQ by 5:00 PM today, June 

7 21, 2012 whether sent via U.S. mail or via e-mail or via FAX. Written comments can be mailed 

8 to Jim Wagner, Air Quality Planning Section, Arizona Department of Environmental Quality, 

9 1110 W. Washington Street, Phoenix, Arizona 85007 or jw3@azdeq.gov. Comments may also 

10 be faxed to (602) 771-2366. 

11 

12 Comments made during the formal comment period are required by law to be considered by the 

13 Department when preparing the final state implementation plan. This is done through the 

14 preparation of a responsiveness summary in which the Department responds in writing to written 

15 and oral comments made during the formal comment period. 

16 

17 First, we will present a brief overview of the proposed revision to the state implementation plan. 

18 

19 Secondly, I will conduct a question and answer period. The purpose of the question and answer 

20 period is to provide information that may help you in making comments on the proposed 

21 revision. 

22 

23 Thirdly, I will conduct the oral comment period. At that time, I will begin to call speakers in the 

24 order that I have received speaker slips. 

25 

26 Please be aware that any comments at today's hearing that you want the Department to formally 

27 consider must be given either in writing by the deadline or on the record at today’s hearing 

28 during the oral comment period of this proceeding. 

29 

30 At this time, Diane Arnst will give a brief overview of the proposal. 

31 * * * * * 
3

1 The Nogales area was designated as a "moderate" nonattainment area for the 1987 

2 24-hour PM-10 National Ambient Air Quality Standards (NAAQS) by operation of law 

3 upon enactment of the 1990 amendments to the Clean Air Act (CAA). The planning 

4 area includes all of the City of Nogales, and portions of the Rio Rico Southwest and Rio 

5 Rico Southeast communities. 

6 

7 As required by the 1990 amendments, Arizona submitted a State Implementation Plan 

8 for the Nogales PM-10 Nonattainment area in November 1993. The Environmental 

9 Protection Agency (or EPA) found the plan to be complete, but did not take final action 

10 on it. The plan included control measures that brought the Nogales area into attainment 

11 of the PM-10 standard by the December 31, 1994, deadline established by the 1990 

12 Clean Air Act amendments. EPA published a Determination of Attainment by 1994 in 

13 the Federal Register on January 11, 2011. The Nogales area continued to meet the PM14 10 standard through 1998. The area has been in and out of attainment since then. 

15 

16 The Proposed State Implementation Plan for the Nogales Nonattainment Area will 

17 ultimately serve as a replacement for the 1993 plan. Clean Air Act Section 179(B) 

18 provides that any area that establishes to the satisfaction of EPA that it would attain the 

19 PM-10 NAAQS “but for emissions emanating from outside the United States” shall not 

20 be subject to certain Clean Air Act requirements, including demonstrations of 

21 reasonable further progress in air quality, demonstrations of attainment, and 

22 contingency measures. The proposed plan includes four technical demonstrations that 

23 Nogales, Arizona would be in attainment of the PM-10 standard "but for" emissions 

24 originating in Nogales Municipality, Sonora, Mexico. ADEQ worked closely with EPA 

25 Region IX to develop the Emissions Inventory of sources in Arizona and sources in 

26 Sonora contributing PM-10 emissions to this air quality planning area and to develop the 

27 technical demonstrations. The most significant source category in Nogales, Arizona is 

28 fugitive dust from unpaved roads. All public roads in the City of Nogales have been 

29 paved and accepted into the City’s Street maintenance Program. ADEQ estimates that 

30 134.4 miles of unpaved roads in the Rio Rico portion of the planning area have been 

31 double chip-sealed and approximately 53 miles of unpaved roads remain. The proposed 
4

1 plan also demonstrates that all other applicable requirements of the Clean Air Act have 

2 been met.

3 

4 Mr. Friedl: Thank you, Diane. This concludes the explanation period of this proceeding on the 

5 proposed revision to the state implementation plan. 

6 

7 * * * * * 

8 Mr. Friedl: Are there any questions before we move to the oral comment period? 

9 QUESTIONS 

10 This concludes the question and answer period of this proceeding on the proposed state 

11 implementation plan revision. 

12 

13 * * * * * 

14 Mr. Friedl: I now open this proceeding for oral comments. Does anybody wish to make a 

15 comment? 

16 COMMENTS 

17 Mr. Friedl: This concludes the oral comment period of this proceeding on the proposed state 

18 implementation plan revision. 

19 

20 * * * * * 

21 If you have not already submitted written comments, you may submit them to me at this time. 

22 Again, the comment period for this proposed revision to the state implementation plan ends at 

23 5:00 PM MST today, June 21, 2012. 

24 

25 Thank you for attending. 

26 

27 The time is now 2:33 PM. I now close this oral proceeding. 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
 

REGION IX
 

75 Hawthorne Street
 

San Francisco. CA 94105·3901
 

June 21, 2012 

Mr. Eric Massey, Division Director 

Air Quality Division 

Arizona Department of Environmental Quality 

1110 West Washington Street 

Phoenix,Arizona 85007 

Re: EPA comments on the Proposed State Implementation Plan (SIP) for the Nogales PM10 

Nonattainment Area 

Dear Mr. Massey: 

On June 20, 2012, Regional Administrator Blumenfeld signed a Federal Register Notice proposing 

approval of Arizona's "Proposed State Implementation Plan for the Nogales PM10 Nonattainment 

Area." As described in this notice, the U.S. Environmental Protection Agency's (EPA's) proposed 

approval of the plan's motor vehicle emissions budget (MVEB) is contingent on the submittal of a 

revised MVEB that includes road construction dust (see generally, 40 CFR 93.122(e)). We, therefore, 

request that the Arizona Department of Environmental Quality (ADEQ) submit a revised MVEB for the 

Nogales PM I0 SIP that includes road construction dust, following the State's procedures for submitting 

a SIP revision to EPA. We request that the revised MVEB be submitted to EPA expeditiously, so we 

can resolve this issue in our final action which we expect to take in late July. 

We regret our contribution to the omission of road constructi<m dust from the MVEB and appreciate the 

extra time and effort it will take from your staff to make this correction. We look forward to continued 

collaboration with ADEQ. If you have any questions or concerns, please contact me at (415) 972-3854, 

or Jerry Wamsley at (415) 947-4111. 

Lisa Hanf, Manager 

Planning Office, Air Division 

Printed (HI Recvcled Paper 
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James Wagner

From: Beverly Chenausky [bchenausky@azdot.gov]

Sent: Friday, June 15, 2012 1:35 PM

To: James Wagner

Subject: Comments provided on Draft Nogales PM10 Nonattainment Plan

Page 1 of 2

7/10/2012

Jim, 

 

I have included a few comments on the proposed Nogales Moderate Area PM10 State 

Implementation Plan (SIP) for your review and consideration. 

 

Page ES-5 – Last sentence first paragraph states “Each new travel plan” the word travel should 

be replaced with transportation. Additionally because Nogales is an isolated rural area and does 

not contain a MPO the frequency requirement of conformity with the MVEB of every four years 

is not applicable. In rural areas conformity done when an FHWA/FTA project needs approval 

not every four years, please remove reference to the four years in this sentence. 

 

Page 2, Table 1.2 (and elsewhere) – General inquiry on why Census population is used instead 

of Department of Administration Population estimates? Please refer to Item 10 from The 

Governor’s Executive Order 2011-04 Designating the Arizona Department of Administration as 

the State Agency Responsible for Preparing Official Population Estimates and Projections. 

http://azgovernor.gov/dms/upload/EO_2011-04.pdf

 

Page 24 – Wind Direction and Pollution Rose – it might be helpful for those not familiar with 

use of Wind Rose or meteorological terms to explain in more descriptive detail what the Wind 

Rose and Pollution Rose show as multiple features are displayed in one diagram, as an example 

describe what the length and thickness of the bar represents. The message is that the frequency 

of winds blowing (and pollution concentration) to Mexico from Arizona is small in comparison 

to the number of days the wind blows pollution to Arizona from Mexico, instead of referring to 

Appendix D maybe a summary of findings on what the data shows added to this section would 

be helpful. As a general observation, the SIP relies heavily on referring people to an appendix for 

further explanation, some of the information contained in the appendixes should be summarized 

or described in more detail throughout the SIP. 

 

Page 48 – In relation to MVEB Table 7.1, is it necessary to split out the Mobile portion into 

Gasoline and Diesel categories? It is likely that the personal vehicle fleet (gasoline fleet) would 

increase at a greater rate than diesel, any savings in emissions from diesel should be able to be 

used to offset any increase in gasoline emissions; as such this category should be combined. 

Additionally, please explain what emissions are contained in the Mobile category directly in this 

section instead of referring to Appendix B and be consistent with the categories used. 

Specifically, Page 15 of Appendix B - States “EPA ran the MOVES model for 2011 to produce 

County-wide estimates for exhaust, brake, and tire-wear.” the budget in Table 7.1 should thereby 

list exhaust, brake and tire-wear for clarity. The EPA continues to explain that they “used a .569 

ratio to reflect the emissions in non-attainment area” this is an important point to make directly 

in the SIP document for ensuring consistent planning assumptions between the SIP and any 

necessary conformity analysis. 

 

Thank you, 

 

Beverly T. Chenausky
~~~~~~~~~~~~~~~~~~~~~~~~ Multimodal Planning Division - Air Quality

Arizona Department of Transportation

206 South 17th Avenue, Mail Drop 320

Phoenix, AZ 85007

(602) 712-7487 Office

(602) 712-3046 Fax

bchenausky@azdot.gov

 ________________________________ 

Confidentiality and Nondisclosure Notice: This email transmission and any attachments are intended for use by the person(s)/entity(ies) named above 

and may contain confidential/privileged information. Any unauthorized use, disclosure or distribution is strictly prohibited. If you are not the intended 

recipient, please contact the sender by email, and delete or destroy all copies plus attachments. 

. 

Page 2 of 2

7/10/2012
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1

Arizona Department of Environmental Quality 

Air Quality Division 

July 23, 2012 

RESPONSIVENESS SUMMARY 

to 

Testimony Taken at Oral Proceeding and Written Comments Received on 

the Proposed Nogales PM10 State Implementation Plan Revision 

The oral proceeding on the proposed Nogales PM10 State Implementation Plan (SIP) Revision was held at 

2:00 p.m., Thursday, June 21, 2012, at the Nogales Chamber of Commerce, 123 West Kino Park Place, 

Nogales, Arizona. No oral comments were received. The Arizona Department of Environmental Quality 

(ADEQ) received two written comments from organizations during the public comment period, which 

ended June 21, 2012. The public comments and ADEQ’s responses are described below. 

Errata 

EPA Region IX corrected minor miscalculations in emissions estimates for onroad mobile sources in 

Appendix B. The SIP was revised accordingly: 

 On page ES-4, Figure ES-4, "Other" emissions and annual PM10 estimate were corrected. 

 On page 13, paragraph 2, line 1, the annual PM10 estimate for 2008 was corrected. 

 On page 13, Figure 3.1, the annual PM10 estimate for 2008 was corrected. 

 On page 14, Table 3.2, the emissions estimates for onroad mobile sources were corrected. 

 On page 15, Table 3.3, the emissions estimates for onroad mobile sources were corrected. 

 On page 19, Figure 4.2, the annual PM10 estimate was corrected. 

 On page 47, paragraph 4, lines 5 and 6, the percentages for onroad emissions were corrected. 

 On page 48, paragraph 1, line 1, the 2011 Motor Vehicle Emissions Budget was corrected. 

 On page 48, Table 7.1, road the estimates for onroad mobile sources were corrected. 

The following typographical and grammatical errors have been corrected in the Final version: 

 On page 1, paragraph 2, line 1 was corrected from “Section 1.1.2 describes the climate and 

physiography of the Nogales NA; Sections 1.1.3 and 1.1.4 provide an overview of the 

demographics and economy of the Nogales area” to “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.” 

 On page 4, paragraph 1, line 2, a duplicate footnote 8 was removed. 

 On page 6, line 7, “Table 1.4” was changed to “Table 1.6”. 

 On page 15, paragraph 1, line 7 was changed from "As discussed in Section 2.0...” to "As 

discussed in Section 1.0," 

 On page 16, footnote 20, line 2 was changed from "2008 and 2011 Emissions Inventories for the 

Nogales NAA" to “2008 and 2011 Emissions Inventories for the Nogales NA” 

 Figure 4.1 was moved from page 18 to page 17. Table 4.1 was moved from page 17 to page 18. 

The Table of Contents was updated to reflect these changes. 

 On page 35, bullets 2 and 3, the date of the exceedance was changed from 28 to 26. 
2

 On page 38, paragraph 4, line 8 was changed from “DPSNA, and...” to “Nogales NA, and...” 

 On Page 39, paragraph 3, line 2 was changed from “...where OHV’s can be used within its 

borders” to “...where off-highway vehicles (OHVs) can be used within its borders...” 

Public Comments 

Commenter #1: 

Comment: Page E5, paragraph one, last sentence, the commenter stated that the term “travel plan” should 

be changed to “transportation plan”. The commenter also stated that because Nogales is an isolated rural 

area and does not have a metropolitan planning organization, the frequency requirement to determine 

conformity with the motor vehicle emission budget (MVEB) is not every four years, but determined when 

new federal projects take place. 

Response: On page ES-5, paragraph one, the last sentence was changed from “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” to “Each new transportation plan must 

be shown to conform with the motor vehicle emissions budget (MVEB) and upon any amendments, 

including a new regional emissions analysis.” 

Comment: The motor vehicle emissions budget (MVEB) on page 48 splits Mobile emissions into two 

categories, but it is likely that the personal vehicle fleet (gasoline fleet) would increase at a greater rate 

than diesel, and any savings in emissions from diesel should be able to be used to offset any increase in 

gasoline emissions; as such, this category should be combined. This section should explain what 

emissions are contained in the Mobile category directly instead of referring to Appendix B. The 

categories used should be consistent. 

Response: The third paragraph on page 47 explains the sources included in MOVES projections. Table 

7.1 on page 48 now combines diesel and gasoline emissions. 

Comment: Page 15 of Appendix B states “EPA ran the MOVES model for 2011 to produce county-wide 

estimates for exhaust, brake, and tire-wear." The budget in Table 7.1 should thereby list Exhaust, Brake 

and Tire-wear for clarity. 

Response: Table 7.1 now lists Exhaust, Brake and Tire-Wear as sources included in Onroad emission 

estimates. 

Comment: In Appendix B, the EPA explains that in the 2011 emissions inventories EPA used a .569 ratio 

to allocate countywide emissions to the non-attainment area. This is an important point to make directly 

in the SIP document for ensuring consistent planning assumptions between the SIP and any necessary 

conformity analysis. 

Response: On page 47, two sentences were added to paragraph four to address the commenter's concerns. 

"The estimates were then scaled to the Nogales NA based on Census Bureau population data. To be 

conservative and to reflect the most current Census data, a 0.569 ratio was used instead of the 0.551 ratio 

used for 2008 population-based allocations."
3

Comment: The commenter asked why Census population data was used instead of Arizona Department of 

Administration data, as required by Executive Order 2011-04. 

Response: 40 CFR 93.110 requires transportation conformity determinations to be based on the latest 

planning assumptions. For some categories in the emissions inventories in Chapter Four, EPA scaled 

countywide estimates to the nonattainment area based on population. After reviewing both 2010 U.S. 

Census population data and Arizona Department of Administration (ADOA) annual official estimates 

released December 15, 2010, EPA opted to use Census data to allocate population-based emissions. For 

clarity and consistency, Census data is used throughout the SIP. The Arizona State Demographer's office 

approved the use of Census data in June 2011. ADOA is required to release new population projections 

based on U.S. Census data by December 31, 2012, to replace projections last issued by Arizona in 2006. 

Commenter #2

Comment: The MVEB must include emissions from road construction projects to meet the requirements 

established in CFR 93.122(e). 

Response: Road construction emissions estimates are now included in the MVEB. 
ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY 30 DAY PUBLIC 

COMMENT PERIOD AND OPPORTUNITY TO REQUEST A HEARING ON 

REVISIONS TO THE NOGALES MODERATE PM10 MAINTENANCE PLAN 

The Arizona Department of Environmental Quality (ADEQ) is holding 30 day public 

comment period beginning with the publication of this notice on July , 2012, for 

further revisions to the proposed Nogales Moderate Area PM10 State Implementation Plan 

(SIP). In response to comments received during the initial public comment period that 

began May 18, 2012, and ended June 21, 2012. The SIP was revised to include road 

construction dust in the Motor Vehicle Emissions Budget (MVEB) and correct 

mathematical errors in estimates for onroad mobile emissions in both the emissions 

inventory and MVEB. 

If a request for a hearing is received by August 15, 2012, ADEQ will hold a hearing for 

the SIP revisions at 10:00 a.m., August 23, 2012, at ADEQ, 1110 W. Washington Street, 

Phoenix, Arizona, 85007. If no request is received, the hearing will be cancelled and a 

cancellation notice will be posted on ADEQ's calendar (http://www.azdeq.gov/cgibin/vertical.pl).The public may also call (602) 771-2388 to find out if the hearing has 

been cancelled. 

All interested parties will be given an opportunity at the public hearing to submit relevant 

comments, data, and views, orally and in writing. Written comments may be submitted 

prior to or during the public hearing and must be postmarked or received by at ADEQ by 

5:00 p.m. on August 23, 2012. 

All written comments should be addressed, faxed, or e-mailed to: 

Jim Wagner 

Arizona Department of Environmental Quality - Air Quality Division 

1110 West Washington Street, Phoenix, AZ 85007 

FAX: (602) 771-2366 

E-Mail: JW3@azdeq.gov 

Copies of the revised PM10 SIP proposal are available for review online at the following 

web address http://www.azdeq.gov/cgi-bin/vertical.pl and in hard copy at the following 

locations: 

ADEQ Records Center 

First Floor, 1110 W. Washington Street 

Phoenix, Arizona 85007 

Attention: Norlene Lara, (602) 771-4712 

Nogales Library 

777 E. Grand Avenue 

Nogales, AZ 85621 

Attention: Suzanne Haddock, (520) 287- 6571 
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