New research led by Washington State University has found that large wildfires and extreme heat waves are happening more often at the same time in the western United States, significantly increasing air pollution. In 2020, for example, harmful levels of air pollution caused by such a combination affected more than 68 percent of the western U.S. (approximately 43 million people) in a single day.
When extreme heat events and wildfires occur at the same time, air pollution magnifies considerably: wildfire smoke increases the amount of fine particulate matter in the air, while the heat mixes the smoke with other pollutants to create more ground-level ozone. While stratospheric ozone is protective, ground-level ozone is a major component of smog and poses a substantial public health burden.
By analyzing air quality monitoring data from 2001 to 2020 across western states as well as parts of Canada, the researchers found that annual population exposure to such extreme combined episodes is increasing by about 25 million person-days a year (a figure counting the number of people affected together with the number of days in which they were exposed to air pollution).
“From every indication we have, the hotter, drier conditions projected for this region are likely to increase wildfire activity and contribute to more widespread, severe heat, which means we can expect to see these conditions happen more often in the future,” said co-author Deepti Singh, an assistant professor of environmental sciences at WSU.
“Preparing for these events is really important. We need to think about who is exposed, what capacity there is to minimize that exposure, and how we can protect the most vulnerable people.”
According to Professor Singh and her colleagues, such events could be mitigated by taking measures to slow global warming, better managing wildfires, and making sure people have access to shelters with air quality filters.
However, the size of these simultaneous air pollution events will make it difficult for a large number of people to avoid their impact. “If there’s such a large region that’s being affected by this air pollution, it really limits where people can go to escape those conditions. You could travel a hundred miles and still not find air quality that is any better,” Professor Singh said.
The study is published in the journal Science Advances.