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FLORENCE — The U.S. Environmental Protection Agency is violating the Clean Air Act by neglecting its legally mandated duties to confront air pollution in western Pinal County, the Sierra Club environmental group alleges in a lawsuit.

The suit filed April 14 in federal court specifically notes high levels of airborne particulate matter with a diameter of 10 micrometers or smaller, called “PM10.”

The West Pinal area includes Casa Grande, Coolidge, Eloy, Florence and Maricopa. The EPA in the past has found “widespread, frequent and in some instances severe violations of the PM10 standard” there. PM10 levels are “among the worst in the nation,” the suit alleges.

The suit specifically names EPA Administrator Andrew Wheeler. “The administrator’s continuous failure to perform his nondiscretionary duties under the (Clean Air) Act poses a significant health risk to Pinal County residents, including plaintiff’s members.” The suit asks for declaratory and injunctive relief, attorneys’ fees and costs.

The suit argues that PM10 pollution poses a serious threat to human health. “These tiny particles can get trapped in the lungs and cause lung tissue damage, leading to chronic respiratory disease, cancer and even premature death. Children, the elderly and people with chronic lung disease, influenza or asthma are particularly vulnerable to the effects of PM10,” the suit says.

Pinal County is not a party to the suit.

Pinal County spokesman James Daniels said the county’s seven PM10 monitoring stations from 2016 to 2018 show readings that are out of compliance with national standards, but “we do not have data to support the assertion that Pinal County levels are the worst in the country. … Long-term trends show the PM10 values are decreasing (improving air quality) over the past 10 years,” Daniels said by email in response to questions from PinalCentral.

The minuscule pollutants that make up PM10 in the area are believed to come from a variety of sources. Both high winds and low-wind conditions make it worse, Daniels said:

“The analysis conducted for the West Pinal PM10 moderate area nonattainment plan in 2015 identified agriculture, construction, unpaved roads, vacant lands and vacant lots as contributors across the area.

“The elevated PM10 occurs under two conditions, high wind and stagnant air conditions. High winds during thunderstorms or frontal passages lift dust off the surface into the air. During low wind or stagnant conditions, dust created by activity is trapped and concentrated near the surface. The contributions vary between the seven PM10 monitoring sites the county operates in the West Pinal area depending on activity nearby.”

Pinal County Director of Air Quality Control Michael Sundlblom said his department issues a daily air quality forecast for the public. It is available two ways: a PDF document is downloaded by visiting Interested people may also sign up for updates on the department’s home page at

In 1987, the EPA set the national ambient air quality standard for PM10 at 150 micrograms per cubic meter, averaged over a 24-hour period, according to the Sierra Club’s suit. To attain the standard, each air quality monitoring site must not measure more than 150 micrograms per cubic meter more than once per year on average over a consecutive three-year period.

But West Pinal monitoring stations routinely recorded two to three times the standard, and several approached or exceeded 600 micrograms per cubic meter, the suit alleges. In 2011, the Maricopa monitor measured 2,318 micrograms per cubic meter — 15 times more than the health-based standard. The Casa Grande monitor has measured 2,040 micrograms per cubic meter, the suit says.

More recent monitoring data from 2016 to 2018 shows the PM10 pollution problem in the West Pinal NAA (“Nonattainment area”) has not improved, the suit says.

The nonprofit Sierra Club is considered to be the oldest and largest grassroots environmental organization in the United States.


Mark Cowling is the county reporter for PinalCentral and covers the town of Florence, San Tan Valley and the surrounding area. He can be reached at