< Wildfire smoke this year woke up places unaccustomed to its effects. Now what?

JUANA SUMMERS, HOST:

This year was a wake-up call for people across the U.S. about the dangers of wildfire smoke. The problem grows every year because of human-caused climate change, which fuels bigger wildfires. As NPR's Alejandra Borunda reports, the health risks are also becoming clearer.

ALEJANDRA BORUNDA, BYLINE: When people on the East Coast woke up on June 6, they knew something was wrong. The sky looked weird, and the air felt thick.

KAI CHEN: Not only we can see the orange sky, but also, we can smell it.

BORUNDA: That's Kai Chen. He's an epidemiologist who studies climate change and health at Yale. He was in Connecticut on that day when smoke from massive fires burning in Canada wafted into the eastern U.S. Millions of people there had never seen that kind of smoke before.

CHEN: Now this year has been making it very clear. So climate change is everyone's problem.

BORUNDA: Chen and his colleagues decided to see how much that smoke affected people, so they tracked down New York City Emergency Department records from that week in June.

CHEN: During that three-day smoke wave period, Asthma Emergency Department visits jumps significantly, about a 44% increase.

BORUNDA: Scientists found that those Canada wildfires and the smoke they caused were almost certainly worse because of human-driven climate change. Sam Heft-Neal is a scientist at Stanford who studies the impacts of wildfires. He's from California, where wildfires are a fact of life.

SAM HEFT-NEAL: I had a lot of friends on the East Coast reaching out, being like, oh, I understand now. This is what you guys have been going through.

BORUNDA: This year Heft-Neal and some colleagues looked at how U.S. air quality has changed in the past few decades since the 1990s, when the country's landmark Clean Air Act was updated. Overall, since then, the country's air was getting much better every year. But since 2015, wildfire smoke from Western burns has erased about two decades worth of improvements. Heft-Neal says that's a reality people across the country will have to accept.

HEFT-NEAL: Years that we've seen in recent times that have been considered outliers will become much more the norm.

BORUNDA: And as that smoke burden grows, so do the health risks.

KRISTIE EBI: The research coming out clearly shows that wildfire smoke is more toxic than air pollution from other sources.

BORUNDA: That's Kristie Ebi, an epidemiologist who focuses on climate and health risks at the University of Washington.

EBI: It's not just trees that burn. Any of the photographs from any of these massive wildfires - the buildings, which means you could have asbestos. You could have carcinogens. The automobiles, all the other structures that burned...

BORUNDA: And that's not all. A recent study in Nature Communications found traces of hexavalent chromium in ash from some wildfires in northern California. That form of chromium causes cancer, and it was probably in the smoke that millions of people inhaled. Scott Fendorf is a researcher at Stanford who worked on the study. He says the research has changed how he thinks about smoke.

SCOTT FENDORF: I'm young and healthy enough that I thought, oh, you know, until it gets super, super-bad, I'm not going to wear a mask. It's just - I don't need to.

BORUNDA: Now, Fendorf says, he has a different attitude.

FENDORF: And now, having new knowledge of what's in that particulate matter, my calculus is totally different. Then I'm going to be wearing N95 mask much, much, much earlier than I would have in the past.

BORUNDA: Researchers like Fendorf hope that as the dangers from wildfire smoke become clearer, more people will take it seriously. That means wearing masks when skies turn smoky or putting air filters in their homes. But health experts say the most important part of the solution is to stop human-driven climate change, which is fueling the wildfires. Alejandra Borunda, NPR News.

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