Efforts to clean up the air in the northwestern U.S. over the past 30 years have periodically been hobbled by smoke from larger and more frequent wildfires, driven in part by climate change.
Air pollution endangers at-risk populations and has links to heart disease and diabetes.
Now, a University of Washington study shows wildfires might at times undo progress made under mandated pollution reductions.
The research appears in the journal Proceedings of the National Academy of Sciences.
Researchers measured concentrations of PM 2.5 — fine airborne particles one-third the size of a red blood cell — at 100 rural monitoring sites nationwide.
Within an area bordered by Nevada, eastern North Dakota and coastal Oregon, particle concentrations from wildfires overwhelmed human reduction efforts.
Arizona reduced its count during the study period of 1988-2016, but progress was muted in the state's fire-prone areas.
