A new report on air quality across the U.S. offers a cloudy prognosis on the long-term health of about 156 million residents who live in areas that received an "F" in smog and soot pollution.

Weakening or rolling back longstanding environmental regulations would worsen the problem, the American Lung Association assessment says.

The American Lung Association report finds that climate events are causing more people in the U.S. to breathe toxic air even as other pollution falls.