How Many People Will This Smoke Kill?

I went for a walk on Wednesday. I intended only to go as far as the first intersection — just to get a quick glimpse of how my New York neighborhood has been transformed by the smoke — but each block revealed itself to be stranger and yellower than the last. Mesermized and horrified, my “just stepping out” stretched into a longer walk as I wandered further and further away from the relative safety of the indoors, where my air purifier was on full blast.

By the time I returned home, the stupidity of my decision had struck me — physically. My throat burned and my voice was hoarse; my head pounded; and my eyes were goopy from the smoke. I’d inhaled something — millions of somethings — that my body was vehemently rejecting. How bad, I wondered in a hypochondriacal panic, was my mistake?

It is almost certain that this smoke will kill people. Many will be elderly or people with pre-existing serious health conditions; some of them may be unborn; some may be people who labor outside. But what we do know is that smoke this bad and that lasts for this long is deadly. One widely cited study by 70 international scientists found that short-term exposure to wildfire smoke causes around 3,193 deaths in the U.S. per year (“short-term” means just three days or less; other studies of short-term wildfire deaths found mortality slightly lower) and this week is already a top-three wildfire pollution event of all time for the nation.

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Wildfire smoke is particularly scary because it contains teeny tiny particles called PM_2.5 that are small enough to enter our lungs and even our bloodstreams. PM_2.5 particles are present at some level in every urban environment but wildfire-related PM_2.5 is believed to be much more toxic than other normal “ambient” particles because of all the yucky things that burn up in fires.

The link between elevated PM_2.5 particle concentrations and increased mortality can be dramatic. The aforementioned international study on wildfire-related PM_2.5 and daily mortality found that “all-cause mortality” — that is, deaths that aren’t accidents — increases by 1.9%, cardiovascular mortality by 1.7%, and respiratory mortality by 1.9% with every bump of 10 micrograms of pollutant per one cubic meter of air. If New York’s PM_2.5 concentration averages, say, 75 micrograms over three days this week (the concentration roughly expected for an average AQI of 150), that would mean people of all ages are 12% more likely to die than they otherwise would be.

To be clear, this doesn’t mean there is a 12% chance you will die this week, but rather that the odds of you dying are 12% higher than they are on an average given day. A young healthy person isn’t likely to die of non-accidental causes on a random normal day, so the danger of wildfire smoke exposure killing you tomorrow is still wildly low. But those numbers go up if you’re elderly or have a heart or respiratory condition to begin with; asthma hospitalizations also, naturally, spike during smoke events.

Put another way, wildfire smoke is an exacerbating factor of serious health conditions. In one study, the risk of dying of a heart attack in the five days after exposure to significant wildfire smoke was elevated by 6.3%; by another, the risk of having a stroke jumps 22% following smoke exposure. These differences are not insignificant; it means there will be people who die from heart attacks or strokes who might not have if the air had otherwise been clear.

But of course, these projections are all speculative, which is why figuring out a death toll for the 2023 smoke event will be a tricky and delicate thing to do. No single death can be blamed just on “smoke.” Researchers can use the established link between elevated PM_2.5 levels and higher mortality rates to do back-of-the-envelope estimates of short-term deaths — it’s how University of Washington researchers projected about 200 smoke-related deaths immediately after fires in the state in 2020 — but crunching the numbers on excess deaths takes patience and time and remains inexact. A study that identified 133 excess cardiorespiratory-related deaths caused by wildfire-smoke exposure during the 2003 southern California fire season took nearly a decade to make it into print.

Short-term deaths, of course, are not the whole story either. One of the major concerns about wildfire smoke is what exposure does in the long term — hour after hour, week after week, and season after season. The East Coast had never needed to worry about that sort of prolonged exposure before. But perhaps now it might.

It may be months yet before we know how bad this smoke event was for the East, and years before we can say with much, if any, certainty. My smoky walk outside probably won’t kill me and, good news, yours probably won’t, either. But “probably” is more than I’d personally like to chance for a few yellowish pictures. Be smart. No poison is always better than “some.”