Salt Lake City continues to climb a list ranking America’s most polluted cities, in spite of the state’s progress in reducing air pollutants that accumulate during its wintertime inversions.

According to a yearly report by the American Lung Association, the Salt Lake City metro area — including Orem and Provo — is now the 18th most ozone-polluted city in the U.S., following cities predominantly located in California. It was ranked 20th in last year’s report.

JoAnna Strother, regional director of public policy of the Lung Association in Utah, said the report found unhealthful levels of ozone put Utahns at risk for premature death, asthma attacks and poor health effects for those already breathing impaired.

“Across the nation,” Strother said in a written statement, “the report found continued improvement in air quality, but still, more than four in 10 Americans – 133.9 million – live in counties that have unhealthful levels of either ozone or particle pollution, where their health is at risk.”

“We can and should do more to save lives,” Strother said.

California’s population centers have long been associated with ozone, which forms on warm summer days when sunlight triggers chemical reactions between other airborne contaminants including emissions from cars. But ozone remains a relatively new issue to the Wasatch Front, which has more commonly struggled with wintertime particulate pollution.

Salt Lake City remains the eighth most polluted city for short-term spikes in particulate pollution, according to the association’s annual State of the Air report, set to be released Wednesday. That ranking represents an improvement from last year’s seventh place.

America's most polluted cities, according to the American Lung Association

Salt Lake City's more notorious pollutant — small particulates — has improved in recent years.

Top ten for short-term small particulate pollution
  1. Bakersfield, CA
  2. Visalia-Porterville-Hanford, CA
  3. Fresno-Madera, CA
  4. Fairbanks, AK
  5. Modesto-Merced, CA
  6. San Jose-San Francisco-Oakland, CA
  7. Los Angeles-Long Beach, CA
  8. Salt Lake City-Provo-Orem, UT
  9. El Centro, CA
  10. Pittsburgh-New Castle-Weirton, PA-OH-WV
  11. Logan, UT-ID

Source: American Lung Association

The Logan area also improved, dropping from eighth place for particulates in 2017 to 11th this year.

The American Lung Association ranks U.S. cities annually according to the number of days a metropolitan area is found to exceed federal standards for specific pollutants. Salt Lake City experienced more high-ozone days from 2014-2016, than in 2013-2015, the time span covered in the association’s 2017 report.

According to the American Lung Association, ozone has decreased across the nation as a whole.

Salt Lake City has long ranked among the nation’s top 10 urban areas for small particulate pollution, but only broke into the association’s top 20 for ozone last year.

Earlier this year, the U.S. Environmental Protection Agency formally deemed the greater Salt Lake metro area in violation of federal standards for ozone. Utah’s main population center has been in violation of EPA’s federal rules for small particulate pollution for more than a decade.

But while the state appears to be making headway on its particulate problem, Michael Siler, Midvale resident and a Southwest regional board member for the American Lung Association, said he was more concerned about ozone.

America's most polluted cities, according to the American Lung Association

Salt Lake City continues to climb the ranks of the American Lung Association's list of most ozone-polluted cities.

Top ten for ozone pollution
  1. Los Angeles-Long Beach, CA
  2. Bakersfield, CA
  3. Visalia-Porterville-Hanford, CA
  4. Fresno-Madera, CA
  5. Sacramento-Roseville, CA
  6. San Diego-Carlsbad, CA
  7. Modesto-Merced, CA
  8. Phoenix-Mesa-Scottsdale, AZ
  9. Redding-Red Bluff, CA
  10. New York-Neward, NY-NJ-CT-PA
  11. Salt Lake City-Provo-Orem, UT

Source: American Lung Association

Ground-level ozone can burn sensitive lung tissues when inhaled. Because the lung damage associated with ozone exposure is permanent and cumulative, young children are particularly at risk. And Utah tends to have large populations of children, Siler said, and residents who like to recreate outdoors — increasing risks associated with high ozone levels.

“We have a more susceptible population than most,” Siler said, “so ozone troubles me a lot.”

Other factors may also boost Utah’s vulnerability to accumulating ozone, according to James Martinez, vice president of communications for the American Lung Association. Mountains surrounding the Wasatch Front prevent air from moving readily and can trap ozone over populated valleys. Similarly, the area’s bowllike geography traps emissions of all kinds, making more ingredients available for ozone formation in summer.

But while most Utahns are familiar with how these dynamics cause particulate pollution to accumulate in winter inversions, Siler said ozone doesn’t seem to be on most residents’ radar.

As ozone is typically associated with emissions from vehicles, the cities that usually top the Lung Association’s rankings for the pollutant also tend to be the most vehicle-dependent — and Utah is no exception. Yet Siler said many Utahns fail to take steps to reduce their emissions — such as turning off the car while waiting to pick up their kids.

“Folks just aren’t getting the message: Ozone is dangerous,” Siler said. “Ozone is caused by more use of internal combustion engines and folks don’t seem to be doing the simple things they could do to quell those sources.”

Land use patterns on the Wasatch Front have also contributed to worsening air, Siler said. Like other ozone-plagued communities, Utah’s urban areas are given to sprawl, making residents more reliant on driving instead of mass transit.

So while more public education is necessary, the American Lung Association report also aims to sway political leaders that while air quality may be improving in some aspects, Siler said, “we still just have so much more to do.”