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  1. Overview of the Region's Designated Air Quality Planning Organization
  2. Tucson Area Air Quality Trends (2016)
  3. Interactive Eastern Pima County Air Quality Map
  4. Pima Clean Air
  5. What can I do to keep our air healthy?
  6. Carbon Monoxide
  7. Ozone
  8. Particulate Matter
  9. Greenhouse Gases
  10. Real Time Air Information
  11. Air Quality Subcommittee
  12. External Sites
  13. Additional Resources

Overview of the Region's Designated Air Quality Planning Organization

Pima Association of Governments’ Air Quality Planning Program develops regional air quality plans, conducts analyses to insure plans do not adversely affect air quality and ensures that air quality programs comply with all air quality requirements. With increasing concern over climate change and the role of greenhouse gases, PAG's Air Quality Planning program conducts routine emissions inventories of greenhouse gases for the region.

Clean air is essential to the economic viability and wellbeing of metropolitan Tucson, and preservation of our desert ecosystem. Motor vehicle travel, industrial activities, land development patterns and meteorological conditions all affect air quality in the Tucson region. Understanding the primary causes of air pollution and initiating steps to curb pollution are essential for maintaining healthy air.

National standards are established by the U.S. Environmental Protection Agency (EPA) to insure that our air remains healthy and to protect the visibility of our natural areas. Currently, the Tucson region meets federal health standards. However, ground-level ozone, particulate matter and carbon monoxide are of continuing concern.

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Tucson Area Air Quality Trends (2016)

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Interactive Eastern Pima County Air Quality Map

View Pima Association of Governments' interactive maps containing Geographic Information Systems (GIS) data for the Tucson metropolitan area.

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Pima Clean Air

With the Tucson area’s population at 1 million, maintaining healthy air, understanding the sources of pollution and initiating steps to curb pollution are important.

Currently, air quality in the Tucson region is good and meets all of the federal environmental health standards. However, several air pollutants (ground-level ozone, particulate matter, carbon monoxide) are of key significance in our area. Of these three, ground-level ozone is of the greatest concern since increasing levels may exceed the total concentrations recommended by the federal health standard. Although air pollutants are emitted from commercial and industrial sources, the majority of manmade air pollution in the county comes from motor vehicle use.

On October 1, 2015, the EPA announced new primary and secondary ozone standards of 70 ppb.

Please view the FAQ on the New Ozone Standards from PAG's Air Quality Program.

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What can I do to keep our air healthy?

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Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas emitted by motor vehicles and other sources. CO is formed when fuels such as gasoline, wood or coal, are not completely burned. 

Emissions primarily occur from motor vehicle exhausts -- by automobiles, buses and trucks -- and some industrial processes. Carbon monoxide is found in high concentrations along the roadside, especially where there is heavy traffic. Other areas might include parking garages and poorly ventilated tunnels.

CO can affect the cardiovascular and nervous systems and cause death in high concentrations. Lower concentrations of CO have been shown to affect people with heart disease such as angina, can cause dizziness, headaches and fatigue, and at high concentrations, even death.

The U.S. Environmental Protection Agency sets National Ambient Air Quality Standards to protect public health environment for seven air pollutants.

Current CO Standards

  • 1-hour average: 35 parts per million
  • 8-hour average: 9 parts per million

Carbon Monoxide short-term trends

Carbon monoxide (CO) is a localized pollutant that disperses rapidly. In Pima County, on-road motor vehicle exhaust produces about 26% of the carbon monoxide. Non-road vehicles produce about 25% of the county's CO emissions.

CO concentrations tend to be highest in winter, when temperatures are cool, wind speeds are low and a temperature inversion is present. This occurs when a stable atmospheric layer restricts the mixing of pollutants.

Since the region violated the EPA health standard frequently in the 1970s, the Tucson Air Planning Area was classified as a nonattainment area for carbon monoxide and a state implementation plan was required to comply with the Clean Air Act.

In 2000, Arizona requested the EPA reclassify the Tucson region in attainment with the national health-based standard for carbon monoxide and, in the same year, the EPA approved a maintenance plan to ensure ongoing compliance. The CO Maintenance Plan was recently updated and approved by the EPA in 2009, with an effective date of January 2010.

The 2008 Revision to the CO Limited Maintenance Plan maintains existing controls and contingency provisions and replaces the 2000 plan. This revision ensures maintenance of the CO standard through 2020.

Carbon Monoxide long-term trends

Since monitoring began in Pima County in 1973, carbon monoxide levels have decreased. The primary reasons for this are due to technological advances with the implementation of the following:   

  • Federal Motor Vehicle Control Program (tailpipe emission standards for new cars)
  • Annual state Inspection and Maintenance Program
  • Oxygenated fuels have been used each winter from September 30 to March 31, since the winter of 1990-1991

High carbon monoxide concentrations tend to occur when wind speeds are low and strong inversions are present. The levels tend to rise following traffic peaks, with the highest levels occurring soon after rush hour.

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Ozone is an invisible gas that occurs naturally in the upper atmosphere (about nine to 13 miles above the earth’s surface), and protects life on earth by filtering out harmful ultraviolet radiation. Ozone at ground level, however, is a harmful pollutant. It is a major component of smog and is the result of complex chemical reactions involving chemical reaction and sunlight. Oxides of nitrogen (NOx) and volatile organics (VOC) (known as precursors to ozone formation) originate from many different sources. Typical urban area sources are emissions from on-road vehicles and off-road mobile sources, such as construction vehicles, planes and trains, and power plants and factories. 

Ozone is a severe irritant to the respiratory system and can cause shortness of breath, coughing, wheezing and stinging eyes. It can damage lung tissue and make people more susceptible to respiratory infections. Ozone is especially harmful to children, the elderly, and those with impaired health.

New EPA Standards - October 2015

On October 1, 2015, the EPA announced new primary and secondary ozone standards of 70 ppb. The previous standard was 75 ppb. The air quality monitoring data from 2014-2016 will be used to determine if an area meets the new standards. The EPA will be issuing more technical guidance on how state and local agencies will implement these new standards.

For more information, please view the FAQ on the New Ozone Standards from PAG's Air Quality Program.

Current Ozone Standard

  • 70 ppb (Annual fourth-highest daily maximum 8-hour concentraton averages over 3 years)

Ozone Trends in Pima County

In Pima County, ozone can be produced at any time of year, due to the high percentage of days with little or no cloud cover, but levels are the highest during summer. Ozone concentrations are usually the highest during summer afternoons, when there is intense sunlight, moderate heat, and stable air conditions.

Levels are also dependent on the topography and air flow within the Tucson valley. High ozone concentrations tend to occur in more suburban and rural sites where there is less NOx to react with and break down the ozone (scavenging).

Local data indicate that the Tucson region experiences ozone levels close to the 8-hour standard set by the EPA. Concentrations tend to be highest in summer when temperatures are warm and wind speeds are low. 

Although ozone levels in Pima County have been relatively constant over the past 15 years Pima County is at 99% of reaching the new standard. If ozone concentrations exceed this standard, stricter regulations limiting emissions from vehicles and industry could be enacted. This translates to increased costs for the public and local businesses and industries. With small efforts from everyone in the community, ozone levels can continue to remain at healthy levels.


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Particulate Matter

Particulate matter is small solid particles or liquid droplets from smoke, dust, fly ash and condensing vapors. It can be suspended in the air for long periods of time. It is generated from travel on paved and unpaved roads, woodsmoke, burning fuels, earth moving, mining, construction, vacant lots and agricultural activities.

These microscopic particles can affect breathing and respiration, cause lung damage and possibly cause premature death. Children, the elderly and people suffering from heart or lung disease are especially at risk.

There are two types of particulate matter that are regulated by the EPA: Coarse Particulate Matter (PM10) and Fine Particulate Matter (PM2.5). The number indicates the size of the particle in microns. Recent research shows that the smaller particles pose a greater threat than the larger particles. 

Current Particulate Matter Standards

  • 24-hour average: 150 µg/m3
  • 24-hour average:  35 µg/m3
  • Annual average:   12 µg/m3

Particulate Matter Trends in Pima County

In Pima County, the natural desert background comprises about one third of the typical particulate matter concentrations. Particulate concentrations tend to be higher in winter and increase during dry periods.

This graph shows the monthly average trend of PM10 and PM2.5 concentrations at the Orange Grove monitoring site for 2015.

For dust control, Title 17 of the Pima County Code outlines activity permits and performance standards required for construction activities.






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Greenhouse Gases

Regional GHG Inventories and Trends

Greenhouse Gases (GHG) are several gases that absorb and emit radiation which trap heat near the earth's surface. Most can be naturally occurring and human generated. Many chemicals in the atmosphere act as greenhouse gases (GHG) because they absorb infrared radiation and trap heat. Naturally occurring GHG include water vapor, carbon dioxide, methane, nitrous oxide and ozone. In addition, some human activities, such as electricity and natural gas consumption, vehicle travel, manufacturing and agricultural practices also produce GHG including carbon dioxide, methane, nitrous oxide and fluorinated gases.

When accessing the amount of human- generated GHG, carbon dioxide equivalents (CO2e), a weighted value, is usually used. This allows the various gases to be compared based upon the relative global warming potential and their persistence in the atmosphere.  

PAG conducts GHG inventories for various communities and government operations in eastern Pima County. Community inventories include GHG emissions from electricity and natural gas use, vehicle travel and waste disposal and locomotive, aircraft and industrial activities. Results from the various community inventories show a similar trend: energy use and transportation are responsible for most GHG emissions and trends generally track population growth.

Government operations’ inventories include emissions produced by energy used in government buildings, water delivery and wastewater treatment and streetlights; government fleet travel and employee commuting, and from waste disposal. The results from the government inventories indicate that the energy used in buildings and in water handling are the major sources of governments’ GHG emissions.

  • Regional Greenhouse Gas Emissions Inventory - (Update pending)

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Real Time Air Information

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Air Quality Subcommittee

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External Sites

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Additional Resources

Southwest Air Quality Forums

Outreach Materials

Air Quality Planning Library

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