The Twin Cities’ air may be dangerously dirty, the Star Tribune reports, citing analysis by the American Lung Association.

The cities’ air quality has been declining steadily, but for the first time in nearly two decades, it may violate federal health standards. Higher levels of particulate matter put residents at greater risk for heart attacks, asthma and other pollution-related illness.

Ramsey County received an F for particulate matter in the ALA analysis. Hennepin County remained at about the same levels as in previous years.

Across the country, air quality improved after the Clean Air Act passed in 1970, regulating big industries. Now, pollution from cars, small businesses and more home products are depleting it.

If air quality standards aren’t met, the Environmental Protection Agency could force the state to develop an air cleanup plan.