Jun Wang lab, University of Iowa.

Wildfires in the western U.S. and Canada have erased air quality gains and caused more premature deaths. This map shows the highest concentrations (in red) of black carbon, a fine-particle air pollutant linked to human respiratory and heart disease.

After half a century of efforts to clean up air quality in the U.S., new research finds the toll from wildfires may be overwhelming health gains in the West.

Using mathematical modeling to bridge gaps in data coverage, the Lancet Planetary Health study ties a rise in wildfire frequency and intensity to 670 additional premature deaths per year in the West from 2000 to 2020.

That’s likely due to increased particles like PM2.5s, but may also stem from black carbon levels, which the authors say have risen 55% each year, mostly due to wildfires.

Though experts do not fully understand the direct health effects of black carbon, the particles do strongly absorb solar radiation and can therefore create a positive feedback that worsens air quality.