Air in central Ohio is getting cleaner — as is the case year after year — but it's nowhere close to clean enough, according to an annual American Lung Association report.

“When a report card comes out, you don’t want to see anything but A’s and B’s," said Ken Fletcher, director of advocacy for the American Lung Association in Ohio. "Ohio has far too many F’s and C’s and D’s for my taste.

"We can celebrate the fact that air is improving, but there’s still a long ways to go.”

The State of the Air report, released Wednesday, tracks smog and soot pollution across 220 metropolitan areas using data from the U.S. Environmental Protection Agency. In all, the Lung Association report says more than 125 million Americans live in counties with unhealthy air.

Soot is made up of tiny bits of exhaust from cars, trucks, power plants, wildfires and even backyard grills. Smog develops in the atmosphere when the sun bakes the gases emitted from tailpipes and smokestacks.

High-enough levels of air pollution can shorten lifespans and cause lung cancer and are particularly dangerous for the young, old and those with breathing issues such as asthma.

The 2017 report found reduced levels of smog and year-round soot pollution across the country, but an unrelenting increase in dangerous spikes of particle pollution. Cities in the country’s western and southwestern regions continue to dominate the report’s most ozone-polluted list.

Results are mixed for Ohio.

The Cleveland metropolitan area ranked ninth-worst for year-round soot pollution nationally, and Cincinnati was tied for 20th. At the same time, the Columbus and Lima metro areas were listed among the country’s cleanest cities for short-term soot pollution.

According to the report, Franklin County reduced its weighted average to five days of unhealthy smog levels from 2013-15. That’s an improvement from the previous report’s 12-day average, but it still earned central Ohio an F for smog.

On those unhealthy days, air quality can be poor enough to put sensitive populations at risk just by walking out the door, Fletcher said.

“It’s pretty dramatic,” he said. “And if you are breathing unhealthy air day in and day out, perfectly healthy people can develop problems down the road.”

Fletcher credited the nation's overall improved air quality to comprehensive federal efforts to reduce greenhouse emissions. But he said recent directives to reduce the U.S. EPA's budget, rewrite oil and gas drilling regulations and scrap vehicle and power-plant emission standards could reverse progress.

“The work that has been accomplished so far is really at risk with what’s being proposed in Washington,” he said. “We need to make sure we don’t do anything to roll back that progress. We need to remain vigilant.”

This year’s smog season is underway, which means the Mid-Ohio Regional Planning Commission is sending out air-quality forecasts.

High levels of pollution trigger alerts warning young people, old people and those with respiratory diseases such as asthma to reduce prolonged or heavy outdoor activities.

No such warnings have been issued so far in 2017, said Evelyn Ebert, MORPC's air-quality program supervisor.

While the region reported 10 high-ozone days in 2016 — up from three in 2015 — it also recorded a higher percentage of good air-quality days than in previous years, she said.

“High-ozone pollution days are becoming much less frequent,” she said. “Overall in our region, we are breathing cleaner air than 20 years ago.”