EPA declared a portion of western Pinal County, Ariz., to be in nonattainment for the 1987 federal PM₁₀ coarse particulate matter standard.

The redesignation is based on EPA’s October 2010 proposal and recent air quality monitoring data for PM_10. Based on comments in response to the 2010 proposal, EPA reduced the size of the nonattainment area, relative to its proposed nonattainment area, by about 36 percent.

Monitoring results showed widespread, frequent, and in some instances, severe, violations over the last decade. In fact, western Pinal County PM₁₀ levels are among the worst in the country.

EPA sets national protective standards for pollutants such as particulate matter that threaten public health. Where air quality exceeds a health-based standard, the Clean Air Act requires the area to be designated as a nonattainment area for that pollutant.

Particulate matter is a serious threat to human health. Major concerns include effects on breathing and respiratory systems, damage to lung tissue and premature death. The elderly, children, and people with chronic lung disease or asthma are especially vulnerable.

The Clean Air Act requires the state to submit a plan containing measures that will reduce airborne particulate matter until the area meets the federal air quality standard. The plan is due within 18 months. EPA is working closely with the Arizona Department of Environmental Quality on the plan and expects a submission soon.

The primary causes of dust pollution in the Pinal County area are from roads, agriculture, feedlots, construction and industrial processes.

Particulate matter is the term for solid or liquid particles found in the air. Some particles are large or dark enough to be seen as soot or smoke. Others are so small they can be detected only with an electron microscope. In 1987, EPA replaced the earlier air quality standard with a PM₁₀ standard. The new standard focused on smaller particles that are likely responsible for adverse health effects because of their ability to reach the lower regions of the respiratory tract and includes particles with a diameter of 10 micrometers or less (0.0004 inches or one-seventh the width of a human hair).

For more information including a link to a map of the nonattainment area, please visit: http://www.epa.gov/region9/air/az/pinal/index.html