Mary Bowerman

USA TODAY Network

A new report tries to clear the air on where America stands in its battle with air pollution.

The 2014 State of the Air report out Wednesday from the American Lung Association presents a good news/bad news mix showing improvements in America's air quality compared with previous decades, but more recently an increase in ozone readings since its 2013 report. Bottom line, the association says, is that 147.6 million people live in areas where air quality remains unhealthy, almost 16 million more than the 2013 report.

"The Clean Air Act has helped us come a long way," says Janice Nolen, assistant vice president at the American Lung Association. "But we have 120 days of unhealthy air in Los Angeles and other places, so we have to keep pushing because we know cleaning up the air has an impact on human health."

The report averaged year-round and 24-hour levels of particle pollution, a mix of tiny solid and liquid particles that come from coal-fired plants and vehicle exhaust, and measured ozone, or smog. Particle and ozone pollution increase the risk of heart disease, lung cancer and asthma attacks, according to the Centers for Disease Control and Prevention.

Of the 25 cities with the worst levels of year-round particle pollution, 18 had lower levels, while five recorded higher levels, and two cities stayed the same. Though some improved, all of the most polluted cities have year-round particle levels that violate health standards, according to the report.

Ozone pollution was also worse as 22 of the 25 most polluted cities experienced more high-ozone days in 2010-2012 compared with 2009-2011. The rise in ozone levels was probably driven by warmer temperatures during those years, according to Nolen, who says communities will need help dealing with warmer summer months when ozone can reach dangerous levels. Those who are most vulnerable are children and teens, those over 65, people who work outdoors and those with respiratory or cardiovascular disease, according to the CDC.

That doesn't mean people need to lock the door and stay inside, says Clayton Cowl, a pulmonologist and occupational environmental specialist at the Mayo Clinic in Rochester, Minn.

"It's important to realize that what's safe varies by person and pre-existing conditions," Cowl says. "For the general population, some of those unhealthy days may not result in any long-term issue."

Cities that ranked as the cleanest cities in 2010-2012 based on measures of ozone and short- and long-term particle pollution were Bangor, Maine; Bismark, N.D.; Cape Coral-Fort Myers, Fla.; and Salinas, Calif.

Nolen says that in terms of air quality, there have been some wins, such as a court case upholding standards limiting power plant emissions of toxic air pollutants and the Supreme Court's decision on cross-state air pollution. She says the next step is the Environmental Protection Agency making a decision on a healthier national ozone standard.

"The national air quality standards become the goal every community has to meet," Nolen says. "The current standard allows too much pollution. The goal is protecting public health, and that can be done by cleaning up the air."

As the summer heats up, people can check air quality online at AirNow.