The Environmental Protection Agency is proposing tighter air quality standards for ground-level ozone, the main component of smog. The agency's proposal would dramatically increase the number of U.S. counties rated as having unhealthy air.
As NPR's Elizabeth Shogren tells Renee Montaigne, the plan comes 10 years after the government set a standard for ground-level ozone levels. The 1997 standards limited smog to 80 parts per billion. The EPA's new limit would lower that number to 70-75 parts per billion.
The agency is conducting hearings on the proposal, which could lead to either tighter controls or a return to the 1997 standards.