Why Extreme Heat Plus Pollution Is a Deadly Combination

Two climate-related health risks are converging with alarming frequency: record high temperatures, and air pollution from things like car exhaust and wildfire smoke. Separately, these conditions can make people acutely sick and exacerbate existing health problems. But what happens when they coincide?

Recently, researchers at the University of Southern California set out to answer that question. Their results, based on mortality data from California between 2014 and 2019 and published at the end of June in the American Journal of Respiratory and Critical Care Medicine, indicate that the combined mortality risk of extreme temperatures and thick pollution is significantly more than the sum of their individual effects.
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As the chart below shows, a person’s odds of dying increased 6.1% on extreme temperature days and 5% on extreme pollution days compared with non-extreme days. But on days with both extreme conditions, the risk of death jumped by 21%.

Like vehicle emissions, wildfires release PM2.5, a type of very fine particulate matter that measures less than 2.5 micrometers across. (For comparison, the diameter of a hair is 30 times larger than the largest of these fine particles.) While the USC researchers analyzed PM2.5 pollution levels regardless of its source, they found that days with extremely high pollution happened to coincide with California wildfire events. “When you consider our top 1% of most polluted days, the pollution concentration is really very, very high… four times higher [than normal],” says Md Mostafijur Rahman, a postdoctoral researcher in the Department of Population and Public Health Sciences at USC’s Keck School of Medicine and one of the study’s co-authors. “That is definitely driven by another source. It’s not like the normal source from the traffic.”

Fine particulate matter can penetrate deep into the lungs and enter the bloodstream, says Francesca Dominici, a biostatistics …read more

Source:: Time – Science


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