The Pittsburgh region recently received an F rating from the American Air Association and is usually in the top 10 worst U.S. cities for air quality, despite the appearance that the air quality is improving.

Now, a new study estimates that poor air quality is having significant and fatal effects.

According to a collaborative report from the American Thoracic Society and New York University’s Marron Institute for Urban Management, the Pittsburgh region had the fourth most air-pollution related deaths of any metro area in the country.

In 2017, the Pittsburgh region, which includes Allegheny County, all of its bordering counties, and Fayette County, suffered 232 deaths related to air pollution, according to the study’s estimates. This was the most of any region outside of California.

For Matthew Mehalik, director of air-quality group Breathe Project, this study is another clarion call for more steps to be taken to reduce Southwestern Pennsylvania’s air pollution.

“It is more ongoing evidence that we have a serious air quality problem,” says Mehalik. “And people that pretend we don’t aren’t doing anyone any favors.”

The study looked at air-quality data from hundreds of U.S. counties, focusing on particulate matter and ozone pollution. It estimated the annual number of deaths, serious illnesses, and missed work days caused by air pollution by using past Environmental Protection Agency studies. This data was used to estimate the likelihood of fatal conditions like heart attacks, lung cancer, and severe asthma attacks, given the levels of air pollution in the region.

The Los Angeles metro area, with a population of 13 million, led the nation in estimated air-pollution deaths at 1,322. But LA had almost the identical amount of air-pollutions deaths per-capita as Pittsburgh, at about one for every 10,000 residents.

According to census figures, about 4.65 million people in LA commute to work in a car alone, compared to about 875,000 in Pittsburgh. Pittsburgh has around 163 solo car commuters per square mile, while LA has about 960 solo car commuters per square mile. In short, LA has almost six times as many cars per square mile spouting air pollution into its region.

The study showed that particulate matter pollution is much more likely to affect Pittsburghers’ health than ozone. The study also shows Pittsburgh’s air pollution levels improving slightly from 2010 to 2017, but the ozone ranking improving much faster compared to the particulate matter ranking. Though Pittsburgh’s 2017 particulate matter deaths were about one-third of what they were in 2010.

Mehalek says 60 percent of Pittsburgh’s air pollution comes from industrial sources. He cites the Clairton Coke Works, which has a history of air-quality violations, but also the Cheswick power plant and the Irving Works and Edgar Thomson Works steel facilities. He adds that policies to lower emissions from mobile sources, like cars, buses and trucks, are also necessary to get Pittsburgh into a healthy air quality range. Without that, he says it will be harder to continue Pittsburgh’s economic rebound.

“We need strong enforcement, and we need the entities that are responsible to clean up their act,” says Mehalek. “As a public health issue, an environmental justice issues, and a future economic viability issue.”