How a dangerous stew of air pollution is choking the United States


Fires and droughts in the western states are getting worse — and they’re combining with industrial sources to threaten air quality and people’s health.

In September 2020, the skies in Oregon turned crimson as dozens of wildfires scorched forests in the Cascade Mountains. In just three days, the blazes engulfed nearly 4,000 square kilometres — more than had burnt in Oregon during the previous 36 years combined.

For two weeks, the acrid air held residents hostage in their homes. The Oregon Health Authority documented a 38% increase in respiratory-related visits to hospital emergency departments during September 2020, compared with the previous month. It was “the worst two-week period I’ve ever experienced for air pollution anywhere — including India, China and Bangladesh”, says Perry Hystad at Oregon State University in Corvallis, who studies the health impacts of the worst air pollution worldwide.

One stark sign of the dangers could be seen in the air quality index (AQI) — a measure of particulate matter pollution (PM), ozone, carbon monoxide, sulfur dioxide and nitrogen dioxide. The US AQI scale runs from 0 to 500, and values more than 300 are considered hazardous to everybody. For two weeks in mid-September, during the most intense burning across Washington state, Oregon and California, the AQI was at 300 and above. The air monitors closest to the fires were shut off or knocked out. On the worst day, southeast of Salem, Oregon, the AQI surged past the scale’s limit; extrapolations by the Oregon Department of Environmental Quality estimate that it would have reached 642.

“These are AQI values that were unheard of” in the region until the past five years, says Dan Jaffe, an atmospheric chemist at the University of Washington in Seattle. Fine particulate pollution reached levels between 4 and 11 times the National Ambient Air Quality Standards (NAAQS) limit set by the US Environmental Protection Agency (EPA). And it didn’t stay in the West; the pollution travelled all the way to New England on the US east coast.

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Nature, 06-12-22