Balmes: Well, you know, I’m a big Tolkien fan, so it seemed like Mordor that day. The sun looked like the Evil Eye of Sauron. The air quality wasn’t even that bad that day, though, because that light was [created by] the smoke plume up high blocking out the sun. We had heavy fog in the marine layer protecting the air we breathe from being really bad. It wasn’t good, but it was actually Friday of last week where there was more sun but the air quality got into “purple,” very unhealthy for everyone.
Wells: When you say purple … I’ve come out to California just recently and the air-quality indicators are all new to me. Can you orient me a little bit?
Balmes: Sure. Your listeners should get familiar with airnow.gov … That will give the air-quality index (AQI) for your location. Zero to 50 is green, and that’s healthy air. Fifty-one to 100 is yellow. That’s moderate, which can start to be a problem for people with preexisting lung disease or heart disease. One hundred and one to 150 is orange, and that’s when it’s especially harmful to people with preexisting heart and lung disease.
At 151 to 200—red—it becomes unhealthy for everyone. Even people without heart and lung disease may experience symptoms. And then 201 to 300, that’s purple. That’s definitely unhealthy for everyone at that point. Even healthy people are advised not to exercise outdoors. Most healthy people will not experience symptoms in the red zone.
James Hamblin: And with the AQI, when you talk about people getting sick, you’re talking about having short-term symptoms versus having long-term effects from levels of exposure?
Balmes: Yes, the AQI is focused on short-term effects, but those short-term effects can be serious for people with preexisting lung and heart disease.
Wells: That is really good to know. I spent a couple of hours outside at 150 and now I feel like I have a cold.
Balmes: That could be related to being outside in the bad air quality. One of the risk factors for smoke exposure is an increased risk of lower-respiratory-tract infections. That’s acute bronchitis and pneumonia, which is particularly problematic in the midst of the COVID-19 pandemic.
Hamblin: Does it increase your risk of having more severe disease once you’ve been infected if you’ve been living in a place that has high levels of exposure to particulate matter versus someplace else?
Balmes: Yes, there’s a building evidence with regard to air pollution, and particulate matter in particular, and COVID-19. The best-studied association is severity of COVID-19, including one study out of Harvard that I believe is actually getting published just this week, where they looked at county-level data. Counties with more chronic exposure to PM2.5—particulates that are 2.5 microns or smaller—had more COVID-19 deaths.
And that’s chronic exposure, not acute heavy exposure. But other studies from China and Italy, for example, suggest that short-term levels of PM2.5 do increase the risk of severe COVID-19. What is less clearly understood, but there are some studies that are suggestive, is whether exposure to air pollution, and particulate matter in particular, increases your risk of getting the infection. There are good reasons to suspect that it would increase your risk of infection, but that’s not been as well established as the severity of COVID-19.