After two years of warnings, Pinal County has been ordered to clean up its air.
The U.S. Environmental Protection Agency has declared that portions of western Pinal County are violating its coarse-dust standard, which limits the amount of PM-10, particles 10 micrometers or less in diameter, present in the air.
Affected are the most populous areas of Pinal County, including the San Tan Valley area, Maricopa, Casa Grande and portions of Coolidge, Florence and Eloy.
State and county air-quality departments now have 18 months to identify where the particulates are coming from and outline what measures will be taken to ensure the levels meet federal standards.
Dust levels must be tamped down by the end of 2018.
Pinal County has some of the worst coarse-dust levels in the country, by EPA estimates. Since 2002, air-quality monitors throughout the county have shown “widespread, frequent and, in some instances, severe” violations of the PM-10 standard, according to an agency statement issued Wednesday.
The EPA sets air-quality standards based on health-related data, and its threshold for acceptable PM-10 emissions is 150 micrograms per cubic meter over a 24-hour period. To remain in compliance, communities cannot exceed the threshold more than three times in three years.