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Office of Border Environmental Protection: Air
Office of Border Environmental Protection Air Quality

Brief History

The coarse particulate matter (PM10) non-attainment status of the three largest Arizona cities along the international border - Nogales, Douglas and Yuma-San Luis - prompted ADEQ to expand its air quality monitoring efforts to Sonoran border cities in the mid-1990s.

In late 1993, ADEQ began monitoring (PM10) on both sides of the border in the cities of Nogales, Arizona and Nogales, Sonora (jointly known as Ambos Nogales.) A comprehensive study was completed in 1999, which included the following components: air sampling of particulate matter (PM), volatile organic compounds, semi-volatile organic compounds, and aldehydes; air emissions inventory; air modeling and human health risk assessment.

Upon completion of this project, ADEQ conducted a similar study in the cities of Douglas, Arizona and Agua Prieta, Sonora. This project included air sampling and the development of an air emissions inventory for both cities. A number of positive actions were taken in Agua Prieta while the study was under way, including extensive road paving, completion of a modern landfill, and tree plantings. The city had a noticeable improvement in air quality for three consecutive years, which prompted ADEQ to not proceed with the modeling and human health risk assessment phases of the study.

Finally, a third comprehensive binational study was undertaken in the Yuma, Arizona-San Luis Rio Colorado, Sonora area in the early 2000s. That project was known as the Western Arizona-Sonora Border Air Quality Study (WASBAQS). Air quality monitoring and emission inventories were completed for this study.

A brief description of these three studies is given below:

Ambos Nogales

Ambos Nogales

The Nogales study was the first intensive air quality border study conducted by ADEQ. The first phase of the study, on hazardous air pollutants (HAP) and particulate matter (PM) in the Ambos Nogales area was completed in November 1995. The study included collecting ambient air concentrations for 60 pollutants, for one year. Samples were taken every sixth day, according to the standard U.S. EPA protocol, and every third day during an intensive study period in the winter season. The sampling was conducted at the Nogales Post Office and at Carrillo Place, a residential neighborhood near the border.

ADEQ contracted the services of Radian International and ENSR Consulting and Engineering for the development of an air emissions inventory and human health risk assessment, respectively. The information collected through the emissions inventory was loaded by ENSR, along with meteorological data, into a three-dimensional computer model that computed pollutant concentrations throughout the area. The model's results were adjusted to align with the measured concentrations obtained during the sampling program. The modeling for spatial and temporal variations of HAP ambient concentrations were then used in the risk assessment study prepared by ENSR.

The risk assessment examined the pollutants, and the sources of the hazardous air pollutants and particulates. It concluded that the primary source of the PM10 concentrations in Ambos Nogales were a result of unpaved roads and that the dominant cause of hazardous air pollutants on both sides of the border were organic compounds resulting from the operation of motor vehicles.

As a result of the work performed in this area, ADEQ generated a report on the main activities that affect the air quality in the region, as well as several actions focused on improving air quality. The full version of this document can be found in the following links:

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Douglas/Agua Prieta

Douglas Agua PrietaAn intensive air quality monitoring study was conducted in the Douglas/Agua Prieta area from January 1999 to February 2002. Its purpose was to determine the temporal and spatial distribution of ambient air concentrations of toxic air pollutants and particulate matter in the region. For the study time period, meteorological data were collected, including upper air data using a wind profiler. An emissions inventory was developed for the area by a contractor, with guidance from ADEQ staff. As part of the emissions inventory development, ADEQ staff used a new approach - coupling Geographic Information System (GIS) software with satellite image processing software to analyze digital high-resolution satellite images (resolution of one meter). This method allowed staff to more accurately identify and locate land uses that contribute to air pollution, such as land with disturbed topsoil, vacant lots, agricultural land, and unpaved and paved roads.

The emissions inventory was used to identify and quantify sources of air pollution in the Douglas/Agua Prieta area. Sources included vehicle traffic, maquiladoras, and disturbed land.

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Yuma San Luis

Yuma/San Luis

With funding provided by U.S. EPA Region 9 , ADEQ conducted a Binational Air Quality Study for the Western Arizona-Sonora Border Region. This study is considered the largest binational air quality study ever conducted in the US-Mexico Border Region. It determined the type and sources of harmful compounds in the air. The air sampling and meteorological monitoring phase of this study took place in 2003-2004. This was followed by an emissions data gathering effort, completed in 2006. The emissions inventory includes an evaluation of the contribution of the various emissions sources, as well as an analysis of the various potential emissions reductions techniques.

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Arizona Sonora Air Monitoring Station

Arizona-Sonora Border Air Monitoring Stations

In the summer of 2011, ADEQ discontinued its cross-border air quality monitoring program in San Luis Rio Colorado, Agua Prieta and Nogales, Sonora due to funding constraints. At the end of 2011, the State of Sonora Commission on Ecology and Sustainable Development (CEDES) implemented a statewide air quality monitoring program, which included stations in Agua Prieta and Nogales, Sonora, and committed to sharing the data with ADEQ. Unfortunately, that effort lasted only for a year and the data that was collected did not meet the Quality Assurance/Quality Control (QA/QC) standards required by ADEQ.

The PM10 equipment that had been operated and maintained by CEDES at the Nogales, Sonora Technological Institute (ITN) was repaired and re-installed by Sonoma Technology, Inc. (STI) in August, 2014, with funding provided by US EPA Region 9. OBEP staff will provide support with the day-to-day operation and maintenance of the equipment for at least a year, in order to ensure adequate data recovery. All data collected at that station will be loaded onto AirNow International, and will be accessible to the public.

ADEQ continues conducting ambient air quality monitoring throughout Arizona. Environmental parameters measured in this monitoring network include criteria pollutants (O3, SO2, PM10, PM2.5, CO, and Pb), air toxics, and meteorology. The following link provides access to a detailed description of the ADEQ Air Monitoring Network.

Currently, ADEQ has air quality monitoring stations in each of the three largest Arizona border cities - Douglas, Yuma and Nogales. An additional PM monitoring station is located at the Paul Spur lime plant in Cochise County. Over the next year, continuous PM10 and PM2.5 monitors will be installed at the Nogales and Douglas monitoring stations. A detailed description of each site can be found by clicking on the link above and scrolling down, or by clicking on one of the following links to access a specific part of the document.

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Border Region State Implementation Plans (SIPs)

When an area within the state violates federal Clean Air standards, ADEQ develops State Implementation Plans (SIPs) to identify the sources of pollution in an area and air pollution strategies that will help to bring the area back into compliance.

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Outreach Efforts

Pollution caused by particulate matter (PM), is one of the principal causes of impaired air quality in the border region. The Arizona Department of Environmental Quality (ADEQ) has identified the burning of wood and garbage, soil erosion, vehicle emissions, unpaved areas and traffic congestion as contributing factors for this type of pollution. Through the years, several projects addressing these problems have been implemented and some encouraging results have been obtained. However, continuing collaboration with partnering agencies and community groups provide more sustained results.

One outreach effort, the Arizona/Sonora Border Clean Air Calendar, was the main tool used to disseminate basic environmental information to the public for more than a decade. During these years, the calendar’s main pictorial elements were drawings made by students from both sides of the border. The financial support for the calendar was provided by the US Environmental Protection Agency. The last issue of the calendar was for 2014. To view this last edition, access the first link of the list below.

Outreach efforts disseminate both basic environmental education and results of applied projects. ADEQ and other institutions working in the region have accumulated a considerable amount of information that is available to the general population. The following links include access to daily air quality forecasts for the Nogales and Yuma areas, as well as other sources of related information.

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Past Projects

Reducing Diesel Emissions

This section describes OBEP’s past accomplishments in the border region regarding projects and activities related to air quality. A summary of these projects can be found below. Scroll down on this page to read about these projects or click on the appropriate link to jump to the selected topic.

  • Reducing Diesel Emissions through Retrofit Technology
  • Arizona/Sonora Border Clean Air Calendar
  • Schools Chemical Cleanout Project

Reducing Diesel Emissions through Retrofit Technology

Between 2005 and 2010, ADEQ conducted several projects focused on retrofitting buses used by schools or school districts within Santa Cruz County. ADEQ also conducted projects to retrofit diesel haul trucks that frequently cross at Nogales' Mariposa Port of Entry (POE). These projects were grant-funded by the U.S. EPA, with funding being delivered either directly to ADEQ or through the Border of Environment Cooperation Commission (BECC).

Santa Cruz Valley Unified School District (SCVUSD) #35, Rio Rico, Arizona

ADEQ conducted a project to retrofit school buses at the Santa Cruz Valley Unified School District (SCVUSD). The school buses were retrofitted with either Diesel Oxidation Catalysts (DOCs) or Diesel Particle Filters (DPFs), which provide 20-30% and 90% reduction in particulate matter emissions respectively. A total of 31 school buses were retrofitted: 28 with DOCs and three with DPFs. The use of biodiesel fuel (B20) provided an additional 10% reduction of diesel emissions. SCVUSD provided an approximately 80% cost match to leverage funds for the purchase and installation of a storage tank to be used exclusively for biodiesel fuel.

TABLE 1 - Retrofitting Equipment Technical Data
Based on MFG SpecsPM ReductionCO & HC ReductionNox ReductionEngine Type RequiredFuel Type RequiredOther
DOC20% - 30%50%MechanicalNo specialized fuel required
DPF90%5% - 10%Electronic engines built after 1994 (all makes)Ultra low sulfur dieselParticulate Filter Required

Nogales Unified School District (NUSD) #1 and Little Red Schoolhouse, Nogales, Arizona

This project was initiated after the SCVUSD retrofits were completed. Only DOCs were installed on five NUSD school buses and three Little Red Schoolhouse school buses. The use of biodiesel was suggested, but never implemented due to the lack of a local provider.

Patagonia Elementary School District (PESD) and Patagonia Union High School District (PUHSD), Patagonia, Arizona

The Patagonia region was added to the original Nogales area project after receiving an extension of both time and funding. A total of eight buses were retrofitted with DOCs.

Diesel Haul Trucks at the Nogales Mariposa Port of Entry (POE)

ADEQ conducted two separate projects to retrofit diesel haul trucks that frequently cross through the Nogales Mariposa Port of Entry. The Mariposa Port of Entry in Nogales, Arizona is one of the busiest commercial land ports in the U.S., serving as a main entry point for fresh produce coming from Mexico. It has been estimated that during the annual winter produce peak season, from November to March, approximately 136,000 trucks arrive from Mexico to haul produce to the many warehouses in Nogales, Arizona, and approximately 200,000 U.S. trucks arrive to these warehouses to pick up the produce for distribution throughout the U.S.

Vehicle emissions have been identified as one of the main polluting factors in the region and both the long haul trucks and short haul (drayage) trucks crossing the border transporting goods between the two countries are a large contributor of these emissions due to the high number of these vehicles and the frequency with which they cross the border.

Drayage trucks, which are only allowed to travel up to 25 miles on the U.S. side, circulate between the warehouses on both sides of the border, off-loading and re-loading produce and goods. Since these trucks are older and in poorer condition than typical long haul trucks, their emissions are higher. In order to help reduce the diesel emissions produced by these trucks, ADEQ conducted two separate projects to retrofit these types of vehicles.

Working with both the Arizona Department of Transportation (ADOT) and the Nogales, Sonora office for Mexico's Secretariat of Transportation and Communications, these projects identified potential trucks to be retrofitted, and the correspondent technology that could be installed. A total of 71 diesel trucks were retrofitted with DOCs.

TABLE 2 - Number of Retrofitted School Buses in Santa Cruz County (2005-2010)
School District or SchoolRetrofitted Buses
Santa Cruz Valley Unified School District #35 (Rio Rico)31
Nogalies Unified School District5
Little Red Schoolhouse (Nogales)3
Patagonia9
Total Retrofitted School Buses48

TABLE 3 - Total Number of Retrofitted Vehicles in Santa Cruz County (2005 - 2010)
Total Retrofitted School Buses48
Total Retrofitted Drayage Trucks 71
Total Retrofitted School Buses in Santa Cruz County119

TABLE 4 - Number of Retrofitted School Buses in Cochise County (2009 - 2010)
School District or SchoolRetrofitted Buses
Douglas Unified School District #27 9
Palominas School District #1 6
Bisbee Unified School District #23
Naco Elementary School District #23 1
Tombstone Unified School District #1 1
Total Retrofitted School Buses 20

TABLE 5 - Number of Retrofitted School Buses in Yuma County (2011 - 2012)
School District or SchoolRetrofitted Buses
Harvest Preparatory Academy 5
Mohawk Valley School District # 17 2
Wellton Elementary School 2
Antelope Union High School 7
Gadsden School District #32 9
Crane School District #13 17
Somerton School District #11 6
Yuma School District One 11
Total Retrofitted School Buses 59

TABLE 6 - Number of Retrofitted School Buses in Pima County (2012)
School District or SchoolRetrofitted Buses
Amphitheater Unified School District 12
Flowing Wells Unified School District 9
Tucson Unified School District 19
Vail Unified School District 10
Total Retrofitted School Buses 50

TABLE 7 - Number of Retrofitted School Buses in southern Arizona through September 2012
CountiesRetrofitted Buses
Santa Cruz County48
Cochise County 20
Yuma County 59
Pima County 50
Total Retrofitted School Buses 177

Schools Chemical Cleanout Project

School Chemical Management Toolkit

Between 2011 and July of 2013, OBEP personnel supported a project focused on removing old chemicals from several schools in Nogales, Arizona. ADEQ, the Bureau of Applied Research in Anthropology (BARA) at the University of Arizona, and the Nogales Unified School District. The following is a summary of activities conducted:

  1. Selection of participating schools.
  2. Assessment and chemical inventory.
  3. Removal and disposal of outdated chemicals.
  4. Developing a Schools Chemical Management Toolkit.
  5. Developing a Schools Chemical Management Plan.

Arizona/Sonora Border Clean Air Calendar

Outreach efforts have been an important part of the activities that OBEP performs along the Arizona-Sonora border. The goal is to disseminate general information about environmental topics relevant to the region, as well as to inform the public on the type of projects and specific activities that are carried out in the region.

Specific to air quality, these outreach efforts have primarily taken the form of printed materials and sporadic short radio programs in partnership with local government, academic and community partners. One such tool is the Arizona/Sonora Border Clean Air Calendar. It deserves special mention because of its wide acceptance in the region and long duration. The main pictorial material for the calendar consisted of artwork produced by students from both sides of the border, depicting their ideas and solutions for air quality issues. The original calendar started in the Ambos Nogales region, but was briefly expanded to two other Arizona-Sonora border sister communities – Yuma/San Luis R.C. and Douglas/Agua Prieta. For more than a decade, between 2001 and 2013, this outreach effort was financially supported by Region 9 of the US Environmental Protection Agency. The last edition of this calendar, for 2014, can be viewed at the following link.

Arizona/Sonora Border Clean Air Calendar (PDF)















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