This story originally appeared in Environmental Health News by Pittsburgh reporter Kristina Marusic.

The air in Pittsburgh was unsafe to breathe for three months in 2018, according to a new report from the PennEnvironment Research and Policy Center.

The study, published Jan. 28, looks at national air quality data from 2018 in both urban and rural regions. There were 90 days in which half or more air monitoring locations reported levels of particulate matter or ozone pollution above levels that pose “little to no risk” to human health according to the U.S. Environmental Protection Agency (EPA).

Ozone and particulate matter pollution can trigger a host of respiratory and heart issues including heart attacks, asthma and COPD. Particulate matter pollution has also been linked to cancer, premature births and heightened risk of autism. The Pittsburgh region has higher than average rates of asthma and certain types of cancer linked to air pollution.

“Having 90 days of unhealthy air means there’s at least one day a week where just breathing the air in Pittsburgh while you’re just going about your day puts your health at risk,” Zachary Barber, a Pittsburgh-based clean air advocate with PennEnvironment, told Environmental Health News (EHN). “That is completely unacceptable.”

The greater Pittsburgh region also scored all F’s on the American Lung Association’s air quality report card for 2018, and the region had some of the stinkiest and most polluted air in the country at the end of 2019. Previous research has shown that traffic and industrial emissions are the region’s largest sources of air pollution.

​Some modest regional improvement While having unsafe air for a quarter of the year poses serious threats to public health, the report does point to some improvements: The organization’s last report on national air quality, which came out in 2018 and looked at 2016 data, found that Pittsburgh had 121 days of unsafe air — so the region had 31 days of cleaner air this time around. In 2018, Pittsburgh had 39 days in which half or more monitoring locations reported elevated levels of ozone pollution and 72 days with elevated levels of particulate matter pollution, according to the report. In 2016, there were 46 days with elevated ozone pollution and 97 days with elevated particulate matter pollution. “It’s hard to draw an overarching trend from just two years of data on unhealthy air days,” Barber said. “We do know that in general over the past several decades, the trend has been toward improvements in air quality, though it has often been a little slower in Pittsburgh than the rest of the country.”