As smoke drifts, chemical reactions can make it even more toxic. Scientists are working to pinpoint when and where health risks are the greatest — to try to build that into future forecasts.

Vancouver

Recent research indicates that wildfire smoke can become increasingly hazardous to human health as it travels and ages in the atmosphere. As smoke drifts from its source, chemical reactions, particularly oxidation, lead to the formation of free radicals, which are unstable and highly reactive compounds known to damage cells and tissues.

Studies comparing fresh and aged smoke have found that older smoke, especially after interacting with pollutants like nitrogen oxides, is more toxic to lung cells. While concentrations of smoke typically decrease with distance, there is a period where aged smoke remains thick enough to pose significant health risks. Scientists are working to better identify these risk zones and incorporate them into air quality forecasts, emphasizing the chronic danger posed by repeated exposure to wildfire smoke.

Prolonged wildfire smoke could pose increased health risks

This smoke is fresh and already dangerous but get this it may actually be worse for your health a few days from now. I'm standing in front of the active sailor bar fire about two hours northeast of Vancouver. It's just one of the many wildfires that have impacted Canadians this summer. The second worst season on record. So if you've experienced poor air quality recently you're not alone. Think about smoke drifting from Manitoba into Ontario or Hazen, Newfoundland that started in Nova Scotia or BC skies darkened by fires in Washington. Turns out distance matters because as smoke travels it changes. When smoke particles react with other molecules in the air they undergo a chemical process called oxidation. The process of adding an oxygen molecule to a compound and losing an electron. So these compounds with only one electron are unstable and highly reactive. We call them free radicals. More and more research shows that when you inhale them those free radicals can damage cells and tissues. And the longer smoke lingers in the atmosphere the more of these free radicals are made making it all the more toxic to breathe. So you can imagine that this wildfire plume is like a reaction vessel and lots of different processes are happening induced by the water, induced by the sun, induced by the wind and these oxidants. So the molecules that we're breathing are not the same when the plume has aged is what we call it. One study compared two smoke compounds. One that forms right when that fire starts burning and one that forms later when smoke reacts with pollution like nitrogen oxides in the air. So researchers actually exposed human lung cells to both and the results were clear. The old smoke was far more toxic. Here's where it gets tricky. It's not just about how old the smoke is it's also about how much of it you're breathing. Concentrations usually drop as a plume travels so sometimes the risk can actually be lower the farther away you are. But there's a sweet spot or more like sour spot where the smoke has had time to build up those toxic free radicals and is still thick enough to make it into your lungs in harmful amounts. It's a question that is debated at the moment. Is it worse to be exposed to aged smoked or to fresh smoke and that will also depend on what the smoke is. So is it from a burning home? Is it from a burning forest? Scientists are working hard to figure out exactly where that zone is for each fire and they hope to start building that into smoke forecasts soon. I mean here's the thing in the end it doesn't matter if the fire is right behind you or coming from across the country if air quality is poor the risk is real and remember that this is about repeated exposure. This is a chronic problem so if we are exposed more and more which is the case with a lot of Canadians across the country now and we are exposed to the smoke over and over again and that's what is problematic. Wildfire smoke is bad for our health but science is telling us it's even worse than we thought and it doesn't get better with distance it gets more toxic over time.

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Tel Aviv-Yafo

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