The Science Behind Wildfire Smoke
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Hey Short Wavers, Emily Kwong here. Longtime host and friend of planet Earth have gone outside because I want to ask you a question. Our team wants to know what changes are you noticing in your local environment?

Maybe the fire season is lasting longer and longer, or there's an area of your town that just keeps flooding. Maybe there's less bees or a policy or technology that has dramatically changed life in your town. Send us a voice memo with your name, the place where you live, and the change you've noticed in your local environment and have science questions about, and we'll investigate. Our email is shortwave at npr.org. Thanks so much. You're listening to Shortwave from NPR.

Since Tuesday, fires have continued to blaze across Los Angeles, burning over 30,000 acres of land. And this area has a history of wildfires, but as we've heard from officials, this is an extreme case with so many saying they have never seen conditions...

like they're seeing today. This looks ominous and frightening. Those flames are huge. Tens of thousands of people have been forced to leave their homes. You see these mandatory evacuation orders in place. And the scope of these wildfires has caused the air quality

to plummet. Air quality is monitored through the AQI, a color-coded air quality index. And right now, parts of LA are in the orange and red zone, meaning ash, toxins, and superfine particles, the kind that can get lodged in your lungs, are at such unhealthy levels that all people should stay inside. And even as firefighters work around the clock to contain the blaze, the smoke will stay and drift, worsening the air quality well beyond the fires. That's

That's one of the interesting things with smoke is that it doesn't stay where it was emitted. It travels with the wind and can impact large parts of the population well downwind of the fires. Jessica Gilman is an atmospheric chemist for the National Oceanic and Atmospheric Administration. And after wildfires broke out in the American West in 2020, we talked to her about the dangers of inhaling smoke. Any wildfire smoke is toxic.

But Lisa Miller, a wildfire smoke expert at the University of California, Davis, has another concern.

L.A. residents right now face an additional risk from all the homes and buildings that have been incinerated. The man-made materials, so things in cars, things in homes, think of all the synthetic fibers that are present just in your living room, right? In your couch, in your carpet, maybe even your clothes. All of those things can be particularly toxic.

Toxic for everyone, but those particularly at high risk for health complications include pregnant people, kids, and people with pre-existing heart and respiratory health issues, like people with asthma, COPD, and cardiovascular problems. So today on the show, we revisit the conversation between my former co-host Maddie Safaya and Jessica Gilman on the science of wildfire smoke.

what it actually is, how it behaves, and how it perpetuates the cycle for more intense wildfires. At the end, for those of you living in the wildfire zone, we'll also give you tips for how to limit your risk of inhaling smoke. You're listening to Shorewave, the science podcast from NPR. ♪

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I don't know about you, but when I hear the word smoke, it makes me think of like huge thick plumes of different shades of gray sort of blanketing everything, you know, nothing too complicated. For somebody like Jessica, though. Smoke is an incredibly complex mixture of different gases and particles. And if we look just at the gases, there are hundreds to thousands of different gases

gases that are formed in biomass burning. Biomass. We're talking things like trees and brush that burn up in a wildfire.

When it comes to particles in smoke, there's also a huge range, from larger ones in the form of ash and dust that can more quickly settle out of the sky. But you also get really teeny tiny particles on the order of a millionth of a meter in diameter. And those really small particles can stay in the atmosphere for a lot longer. Yeah.

And from the particulates side, the thing that people seem to be the most freaked out about is this PM 2.5 or this little the little particles that are super, super small. Yeah. And there seems to be a lot of that going on right now in California and like large parts of the West. Right.

Yeah, so one of the primary hazardous air pollutants is particles that are called PM2.5s that has an overall diameter of two and a half micrometers or less. And that's roughly about 50 times smaller than a single grain of salt. So really, really small particles. The smaller particles, not only can they travel further distances, but they also have this unique ability to

to follow the sort of micro air currents and can bend around corners and edges and everything. And that means that if you're breathing in smoke,

Those larger particles are going to hit the back of your throat first, but the smaller particles can actually make it all the way down your throat and then deep into your lungs. And that's where they start to cause all kinds of different health effects. One of the most interesting things about smoke is how it behaves, how it interacts with the different layers of our atmosphere, including the layer closest to us called the boundary layer.

And how big that layer is, how thick it is, depends on temperature. So at night, when it's cooler, that layer condenses and comes back down in altitude.

Also, with cooler temps and higher humidity at night, wildfires tend to die down. And when they die down, that's actually when they produce quite a bit of smoke. And that mixing into a more shallow boundary layer just means you get a lot more smoke very close to the ground, particularly at night.

Especially if you're in a kind of a mountain valley where it just starts to pool and accumulate and it's not really diluted or moved out of your immediate area until the sunrise comes, that boundary layer starts to expand, the wind speeds pick up and kind of take the smoke away. Sure. Yeah. I guess...

I didn't, I had no idea that, you know, in areas where there's wildfire burning that the smoke actually kind of settles back down at night. And it makes me think about like, you know, it's night, it's cool, you want to open a window, right? That can be problematic.

It is, yeah. And that's true of most air pollution sources, but particularly so for smoke. In many of the western states, even here in Colorado, it's not necessarily all that common that you have air conditioning. It does cool down quite a bit at night.

And so that is the time people would turn on fans, etc., to try to ventilate the house, get it cool at night. Of course, you're home at night sleeping and breathing all through the night. And so again, that's one way that you can be exposed to smoke that you might not necessarily think of.

And so I think it's important to remember, right? So we're seeing the bonfire, we're seeing the smoke, and all of this smoke doesn't just hang out there, right? Like, smoke really travels, right?

Certain smoke plumes can literally travel the world and go to really, really remote places. And of course, with fires, you know, we're impacted here in the United States right now. But of course, that flips as we go to the next season and then the southern hemisphere. So fire is just a constant emission source, you know, across the globe. And as I said, as it gets emitted and the different layers of the atmosphere can stay in the atmosphere longer. And that just means it can get

carried by the wind currents further and further downwind. And so that smoke can just travel tens to hundreds of miles downwind from the source.

Yeah, yeah. You know, the kicker is, though, when this smoke maybe clears up from the way that we can detect it, like just by going out and being like, oh, I can breathe a little bit easier. It never just disappears, right? Like, you know, smoke feeds into this cycle of climate change, right? Yep. The primary component is going to be related to those particles. And so particles are something that can both cool the climate as well as heat the earth, right?

And so that's where that size and color of the particles really comes into play. And so the white particles that you associate with clouds generally reflect radiation back to space, so that's a cooling effect, right? If you're under a cloud on a super sunny day, you immediately feel better and cooler when that cloud is overhead.

The other way is that those darker particles, the black soot, those are things that readily absorb radiation from the sun, which means when the sun goes down, they can also readmit that radiation back into our atmosphere. And that's what contributes to that, the global warming effect, the greenhouse gas effect that is so important for climate change.

So that's one way that the aerosols play into it. Right. And all of these things kind of feed into, and this is simply put, but these things feed into a longer, hotter fire season. So it's kind of this...

garbage cycle, right? Unfortunately, yeah. So as those particles that are released from biomass burning may impact climate and climate continues to change, which could lead to more fires and so forth, you just get that feedback where it just continues down the wrong path rather than trying to correct itself or balance itself out. Yeah. You know, I feel...

I feel like the wildfires and the smoke are very visual examples of climate change. I mean, do you think that fires could impact how people are thinking about climate change and what needs to be done? I hope so. I mean, there's many different, you know, really visual ways of

climate change with our own eyes. I mean, from the rising sea levels and daytime flooding that's happening in some of the coastal cities to the amount of runoff that you see on the Greenland ice sheet to these huge ice shelves cleaving off of Antarctica. I mean, the signs are all around. The biomass burning is certainly one that impacts a large community of people out west. And as you mentioned, it's a very significant

visceral response. And then with climate change, you know, you often hear of global warming and of course fires represent that heat. And so that's certainly a connection there as well. And so, you know, I can only hope that people start to think about how much their lives will be changed as our climate continues to change and get warmer.

That was Jessica Gilman, a research chemist at the National Oceanic and Atmospheric Administration, talking to former shortwave co-host Maddie Safaya. Now, if you are not sure about your risk of exposure to smoke, look up the air quality index in your region. If you're in an orange zone, especially, or higher, here are some immediate ways to protect yourself.

Stay indoors as much as possible. That also means keeping your doors and windows shut and your pets inside. Avoid lighting candles, gas stoves, and other things that give off pollution. And use a HEPA air filter to remove fine particles from your home's air. Now,

Now, if you do go outdoors, use an N95 mask or a P100 respirator mask. Make sure your mask is approved by NIOSH, N-I-O-S-H. That stands for the National Institute for Occupational Safety and Health, and that the mask fits tightly. Keep that nose covered so that the finest particles are kept out of your system. When the air quality eventually improves, temporarily air out your home.

And finally, follow public advisories to know if air quality changes or if you become part of an evacuation zone. We'll link to more resources in our episode notes. Stay safe, Shore Wavers. This episode was originally produced by Rebecca Ramirez and edited by Viet Le. The update was produced and edited by Rebecca Ramirez and Jessica Young. Special thanks to our colleague, climate reporter Alejandra Burunda. I'm Emily Kwong. Thank you for listening to Shore Wave from NPR.

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