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Wildfire smoke now causes up to half the fine-particle pollution in Western US, study finds

Tony Barboza, Los Angeles Times on

Published in News & Features

Wildfire smoke now accounts for up to half of all fine-particle pollution in the Western U.S., according to a new study that blames climate change for worsening air quality and health risks in both urban and rural communities in recent years.

The study by researchers at Stanford University and UC San Diego found that the concentration of tiny, lung-damaging pollutants known as PM2.5 that are attributable to wildfire smoke roughly doubled between 2006 and 2018, while the share of pollution from other sources like car and truck exhaust declined.

The trend is most pronounced in Western states and highlights the rapidly growing health threat of wildfire smoke. This became shockingly apparent to millions during last year's record-breaking firestorm, which enveloped much of the West Coast in an unhealthy pall for weeks.

Levels of PM2.5 had been steadily improving over the last two decades in which they have been routinely monitored, as a result of regulations that have cut emissions from vehicles and power plants. But those gains started to slow, then reverse, over the last decade or so, according to the study.

"The overall picture is of a stalled and reversed improvement, which is a result of other sources getting cleaner and wildfires getting a lot worse," said Marshall Burke, a professor of Earth system science at Stanford University and lead author of the study published in the Proceedings of the National Academy of Sciences.

The two major factors driving the increase in wildfire smoke are the warming climate and decades of fire suppression that have allowed fuels to build up, according to researchers. They made their estimates by developing a statistical model using fire and smoke data from satellites and readings from ground-based air quality monitoring stations.


Nationwide, wildfires are now responsible for up to 25% of fine-particle pollution, the study found.

"We know wildfires generate smoke. We know smoke is bad for health. But we really didn't have a comprehensive national picture for how much wildfires are contributing to poor air quality," Burke said.

Francesca Dominici, a professor of biostatistics at Harvard's T.H. Chan School of Public Health who was not involved in the research, called it "an excellent study that relies on sophisticated data science approaches" and "provides strong evidence that wildfires are an increasing threat to human health."

Dominici said its findings are concerning, "especially at the time where the U.S. EPA has recommended to retain the current standards for PM2.5 pollution and as we are fighting COVID-19 that is attacking our lungs."


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