On April 14, 2020, the Center sued the U.S. Environmental Protection Agency on behalf of Sierra Club over the EPA’s failure to act on particulate air pollution in West Pinal County. The EPA is violating the Clean Air Act by failing to approve or disapprove Arizona’s plan to address a dangerous type of particulate pollution known as “PM10” in West Pinal County and by failing to make a final determination that the area exceeds national air quality standards for PM10.
Particulate pollution refers to a mix of tiny airborne particles that are often too small to see with the naked eye. The EPA has concluded that particles smaller than or equal to 10 micrometers in diameter, about one-seventh the width of a human hair, present the greatest threat to health. When inhaled, PM10 pollution passes through the natural filters in the nose and mouth and penetrates deep into the lungs. This can cause breathing difficulties, lung tissue damage, cancer, and even premature death. Children, the elderly, and people with chronic lung disease, asthma, or the flu are particularly vulnerable to the effects of PM10 pollution.
The EPA designated West Pinal County as “nonattainment” for PM10 in 2012, and PM10 levels in the area are among the worst in the nation. The health-based standard for PM10 is 150 micrograms per cubic meter. To meet the standard, an air quality monitor cannot measure concentrations greater than this more than once per year on average over a consecutive three-year period. However, multiple monitoring stations in West Pinal County violated the PM10 standard from 2016 through 2018, the most recent period for which certified air quality data are available. During that time, a monitoring site near the City of Maricopa recorded PM10 levels of 1,367 micrograms per cubic meter—nearly ten times the federal standard. Another monitoring site in Stanfield, near Casa Grande, recorded PM10 levels of 1,100 micrograms per cubic meter, or 7 times the federal standard.
In response to a pre-lawsuit letter from the Center, the EPA proposed to find that West Pinal County failed to attain the PM10 standard by the attainment deadline of December 31, 2018. However, the action is not yet final, and part of the relief requested in the Center’s lawsuit is that the EPA commit to a date on which it will finalize the proposed nonattainment determination. Once final, West Pinal County will be reclassified from a “moderate” to a “serious” nonattainment area for PM10. Within 18 months of the reclassification date, the State of Arizona will be required to submit an air quality plan that contains the “best available control measures” to address PM10 pollution and bring the county into compliance with the standard by December 31, 2022.