canada wildfires

Talking to an Air-Quality Expert About That Haze

Photo: Lokman Vural Elibol/Anadolu Agency via Getty Images

For the past week, New Yorkers have awoken to soupy gray skies, a dull-orange sun, and warnings on their phones declaring that going outside is “unhealthy for sensitive groups.” Smoke from more than 400 Canadian wildfires — burning a record-breaking number of acres in what could be the country’s most destructive fire season ever — is drifting across the continent, making air quality from Maine to Minnesota some of the worst on the planet. Inhaling far-flung smoke particles, once a rare occurrence, has now become a perennial event. To make sense of the current haze, I spoke to Daniel Westervelt, a Lamont Assistant Research Professor at Columbia University’s Lamont Doherty Earth Observatory and an air-pollution adviser to the U.S. State Department. We talked about how to protect yourself, when the skies will clear — and why people should prepare for more days like these.

Every time this happens, the science of it really seems impossible. How can these tiny smoke particles travel thousands of miles?

On average, particles in the atmosphere last around seven to ten days. When it rains, the particles interact with the rainfall and then fall out to the surface. The heavier particles can be affected by gravity and don’t need the assist from precipitation to be removed. However, with smoke particles, because the smoke plumes are so hot, they cause a rapid amount of atmospheric convection, which is this strong vertical motion upward. So these particles then get into higher layers of the atmosphere, where they’re not as affected by a lot of the meteorology that can remove them. They can last even longer — on the order of a couple weeks. If you look at average wind speeds, that’s definitely enough time to go from the middle of Quebec to Manhattan.

So what you’re breathing in today is actually weeks-old fire. How much longer will this last?

It’s mostly controlled by meteorology. There’s some discussion today about how there are more plumes of smoke in southern Canada and it looks like they will be coming down to the northeastern U.S. with the prevailing winds. So that’s one of the reasons people are saying that this might last for a couple more days.

The skies have been gray for a week, but air quality really noticeably plummeted over the last day or so. The forecast warns about more “near surface” smoke. What does that mean?

This is what’s called subsidence and entrainment — smoke entering the lowest part of the atmosphere, the planetary boundary layer, where we breathe. If meteorological conditions are conducive, the smoke can actually be breathed in by people at the surface. And the surface is also where the monitoring sites are located.

So when I’m seeing current readings from these air-quality monitors in Manhattan of 125 and 138 — and, farther north, 152 and 164 — what do these say to you? 

If you see AQIs of greater than 100, it’s definitely into the territory of unhealthy, especially for sensitive groups, so for older adults, children, teens, plus people with preexisting conditions — asthma or some kind of respiratory issues — it’s recommended to stay indoors and refrain from strenuous outdoor activity, anything that would require you taking in a higher volume of air that would be laden with these particles.

What are you personally doing?

I’m not going to be doing any biking or running or anything outside today. I’m mostly staying indoors. It’s a good day, if people are so privileged, to use the indoor gym rather than go for a run along the Hudson River.

One way to protect yourself is something we all have handy now — really good masks. Do you endorse wearing a mask if you have to be outside for a long time?

It certainly won’t hurt. Especially the N95 and KN95 masks, which are definitely capable of filtering out the type of smoke particles that are floating around out there. It would give you an extra layer of protection.

But overall — 

People should spend their time indoors. You can also turn on your HEPA filter if you have one, because while indoor air should be lower in particle concentration than outside, we still have a lot of that air that makes its way in one way or another, so we can expect higher concentrations indoors as well. Having some kind of filter is a good thing today. I’ve got mine running right now.

And even if you don’t have an air purifier, if you have an AC unit or central air, you can run that, as long as you remember to change the filter?

Right, exactly.

Are there any other ways to prepare for more of these types of events in the future?

Downloading an app on your phone that tracks air quality. There’s also all kinds of citizen science you can do. People can buy little low-cost sensors that they put in their backyards or hang off their apartment fire escapes. All of this crowdsourced data has really enhanced our ability to diagnose these extreme pollution events that are sometimes caused by fires.

It seems like this happens every year now. Is this our new reality?

There’s solid evidence that wildfires are becoming more frequent, partially due to climate change causing these drought conditions that allow for more fuel to burn. If you went back 20 or 30 years, this was probably a pretty rare occurrence, if ever. Fires are getting more common; they’re getting more intense. And with that comes the possibility that these fires transport their particles to other parts of the world and affect our air quality.

Talking to an Air-Quality Expert About That Haze