The air quality in four Mississippi counties get failing marks from a recent American Lung Association survey .
The study found that DeSoto County in north Mississippi had the worst air quality in the state. Jackson County on the Gulf Coast was second worst.
Lee and Hancock counties also received failing grades.
The findings show that more than 142 million Americans nationwide live in places with high levels of ozone air pollution, commonly known as smog.
The findings were released last week as part of the group's annual "State of the Air'' report. The report examines ozone air quality data taken by the U.S. Environmental Protection Agency from 1998 to 2000.
Nearly 700 counties that were monitored across the country are ranked according to how often their air quality reached unhealthy levels of air pollution. Data was available for 12 Mississippi counties.