An urgent question hangs over catastrophic wildfires: What’s in that toxic smoke?

Scientists are rushing to learn more about those dangerous swirls of gases and particulate matter—and how they threaten our health.

The Angeles National Forest, in Southern California, is engulfed in smoke and flames during last year’s record-breaking wildfire season. The Bobcat Fire, as this one was called, burned more than 115,000 acres. It was one of scores that blew smoke pollution across the western states and beyond—visible as far away as Washington, D.C.

On a rural highway in Northern California, a July traveler’s tire went flat. Metal rim scraped against pavement. The sparks ignited a fire that ripped through dry forest, whirled into flame tornadoes, and roared over tens of thousands of acres, making fuel of everything in its path. When it jumped the Sacramento River and headed for the city of Redding, Keith Bein prepped his new rig—a trailer holding two tiny electric cars, a lot of tubes and instrumentation, and a white contraption that looks like a miniature lighthouse. 

Bein works as an atmospheric scientist at the University of California, Davis campus, about 150 miles south of Redding. By the time he hooked the loaded trailer to his truck and began driving upstate, the 2018 Carr Fire—those sparks ignited near a power plant called Carr—was already one of the biggest wildfires in California history. It had killed six people, including two firefighters. It was burning trees, grasslands, mountain cabins, pedestrian bridges, light posts, fences, parked cars. At the Redding outskirts it had just burned a suburb called Lake Keswick Estates, which meant the full infrastructure of single-family housing: insulation, shingles, refrigerators, paint. 

And everywhere around the Carr Fire’s great trajectory was smoke—billowing, blanketing, spreading thousands of miles beyond the actual flames. Of all the things that foul the air we breathe, it’s wildfire smoke that most fascinates Bein. 

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