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What’s in Wildfire Smoke, and How Dangerous Is It?

Blazes on the West Coast are spewing a haze clear across the country. Along the way, the complex chemistry of what we inhale gets even more complex.

The West Coast’s wildfire crisis is no longer just the West Coast’s wildfire crisis: As massive blazes continue to burn across California, Oregon, and Washington, they’re spewing smoke high into the atmosphere. Winds pick the haze up and transport it clear across the country, tainting the skies above the East Coast.

But what are you breathing, exactly, when these forests combust and waft smoke near and far? Charred trees and shrubs, of course, but also the synthetic materials from homes and other structures lost in the blazes. Along with a variety of gases, these give off tiny particles, known as PM 2.5 (particulate matter 2.5 microns or smaller), that weasel their way deep into human lungs. All told, the mixture of solids and gases actually transforms chemically as it crosses the country, creating different consequences for the health of humans thousands of miles apart. In other words, what you breathe in, and how hazardous it remains, may depend on how far you live from the Pacific coast.

When vegetation catches on fire, it releases a whole lot of carbon in many forms. The sooty stuff you can see is known as black carbon. The major components you can’t see are carbon monoxide—obviously very toxic—and carbon dioxide. When trees absorb carbon dioxide from the atmosphere, they sequester it in their tissues and release oxygen. When those trees catch on fire, that CO 2 goes right back into the atmosphere.

Scientists have been sampling wildfire smoke in the atmosphere with a special plane loaded with a bevy of instruments connected to little tubes that stick out of the aircraft. “Basically, it’s my laboratory,” says Rebecca Hornbrook, an atmospheric chemist at the National Center for Atmospheric Research. These instruments measure conditions like humidity and temperature, along with particulate matter and carbon dioxide, benzene, and formaldehyde—the last two are quite toxic. “By combining all that data together, we’re…

Matt Simon

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