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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.

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