MICHEL MARTIN, HOST:
For millions of Americans, the air this summer has become more dangerous, and wildfire smoke in the West is not the only reason. Even without that, the warming climate threatens to roll back decades of improvements in air quality. Reid Frazier of StateImpact Pennsylvania and the Allegheny Front explains.
REID FRAZIER, BYLINE: One day this spring, after nearly 15 years without one, David Michuk got an unexpected visitor - an asthma attack.
DAVID MICHUK: It's so much worse than I remembered.
FRAZIER: Michuk lives in Pittsburgh. He called a doctor and got medicine to control his symptoms. But this summer, particularly on hot days, breathing has been difficult.
MICHUK: I walk out of my house, and it's like you just walk into this wall of heat and humidity, and it knocks the breath out of you.
FRAZIER: Michuk, who's 29 and hopes to enter nursing school in the fall, says he'd like to go hiking with his friends but has for the most part stayed inside because of his breathing problems in the heat.
MICHUK: I like to walk and do a lot of things outdoors, and it's just been a struggle because I feel like I'm constantly trying to catch my breath.
FRAZIER: One reason why it might be hard for him and others with asthma to breathe - like much of the country, it's been hotter than normal in Pittsburgh. And hot days produce a type of air pollution called ozone, or smog. Deb Gentile is Michuk's doctor and an allergy and asthma specialist.
DEBORAH GENTILE: Basically, it can cause airway inflammation or swelling, tightening of the breathing tube so it's very difficult to move air in and out.
FRAZIER: Gentile says she's had plenty of patients this summer with breathing problems during what would normally be a quiet period between allergy seasons. This coincides with a spike in bad air quality days. Pennsylvania has had nearly the same number of air quality action days already this year as it had in all of 2019. Nationwide, more Americans experienced unhealthy ozone levels in the past five years, according to the National Lung Association. Those years included some of the hottest on record, and 2020 could top them all.
Ted Russell, an atmospheric scientist at Georgia Tech, says heat is perfect for creating ozone.
TED RUSSELL: Ozone is a tricky molecule. It is formed in the atmosphere. It's not emitted directly.
FRAZIER: Russell says ozone is formed by two types of pollution - volatile organic compounds emitted by things like paint and gasoline fumes and nitrogen oxides created by fossil fuel combustion in cars, factories and power plants. You also need sunlight to create ozone. Heat waves, which have been on the rise in the U.S., can speed up the process, Russell says, in part because some of these pollutants evaporate faster on hot days.
RUSSELL: Just like water evaporates faster, but gasoline even faster still. And paints on a hot day - they dry faster.
FRAZIER: There is some good news here. Regulations have led to lower tailpipe and power plant emissions, and thus less ozone around the U.S., says Edson Severnini, an environmental economist at Carnegie Mellon University.
EDSON SEVERNINI: We have made a lot of progress. Like, you see the graphs, and you feel like, oh, my God. Something is - you know, something good has happened.
FRAZIER: But that progress could be upended by climate change. Severnini says ozone starts to really spike above 86 degrees Fahrenheit. He says the number of hot days has already increased since 1980. And as the climate warms, it's expected to double by 2050.
For NPR News, I'm Reid Frazier in Pittsburgh.
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