ATLANTA (AP) _ Metro Atlanta could fall out of compliance with air quality rules under tougher guidelines being considered by the U.S. Environmental Protection Agency, officials say.

Smog _ or ground-level ozone _ is formed when air pollutants from industry, vehicles and other sources react in sunlight.

Atlanta’s ozone level has dropped from more than 120 parts per billion in the 1980s to 80 parts per billion today, the Atlanta Journal-Constitution reported. The lowest level now under consideration by the EPA would put the new limit at 60 parts per billion.

After scientists determined the 1997 ozone standard was no longer safe, federal regulators adopted a more stringent level in 2008. The EPA, however, decided not to implement the standard and is considering an even lower limit. A ruling is expected by the end of July.

A stricter standard on smog could mean that what is now considered a moderate air day may soon be considered unhealthy for children and other sensitive groups, said Rebecca Watts Hull, director of Mothers & Others for Clean Air.

Motorists could play an increasingly critical role in improving air quality as new rules are considered. That’s because half of all smog-forming emissions come from car tailpipes, and Atlanta’s average commute is 35 miles round trip, said Brian Carr of Georgia’s Clean Air Campaign. The nonprofit works to improve the state’s air quality and reduce traffic congestion.

“We’ve got our work cut out for us,” Carr told the Journal-Constitution.