US particulate matter air quality improves except in wildfire-prone areas

Significance Wildfires are a major source of fine particulate matter (diameter <2.5 µm; PM 2.5 ), which is a health hazard. Since the mid-1980s, the total US area burned by wildfires has been increasing, with fires in the Northwest United States accounting for ∼50–60% of that increase. In the Northwest United States, we find a positive trend in the 98th quantile of PM 2.5 in contrast to other areas of the country where PM 2.5 is decreasing. This positive trend in PM 2.5 is closely associated with total carbon (a marker of wildfire emissions). These results support model predictions of increasing wildfire occurrence and PM 2.5 in a warming world.