Wildfire activity is driving summertime air quality degradation across the western US: a model-based attribution to smoke source regions

Over recent decades, wildfire activity across western North America has increased in concert with summertime air quality degradation in western US urban centers. Using a Lagrangian atmospheric modeling framework to simulate smoke transport for almost 20 years, we quantitatively link decadal scale air quality trends with regional wildfire activity. Modeled smoke concentrations correlate well with observed fine-mode aerosol (PM2.5) concentrations (R > 0.8) at the urban centers most impacted by smoke, supporting attribution of observed trends to wildfire sources. Many western US urban centers (23 of 33 total) exhibit statistically significant trends toward enhanced, wildfire-driven, extreme (98th quantile) air quality episodes during the months of August and September for the years 2003-2020. In the most extreme cases, trends in 98th quantile PM2.5 exceed 2 mu g m(-3) yr(-1), with such large trends clustering in the Pacific Northwest and Northern/Central California. We find that the Pacific Northwest is uniquely impacted by smoke from wildfires in the mountainous Pacific Northwest, California, and British Columbia, leading to especially robust degradation of air quality. Summertime PM2.5 trends in California and the Intermountain West are largely explained by wildfires in mountainous California and the American Rockies, respectively. These results may inform regional scale forest management efforts, and they present significant implications for understanding the wildfire-air quality connection in the context of climate driven trends toward enhanced wildfire activity and subsequent human exposure to degraded air quality.

Automated summary

In recent decades, wildfire activity in western North America has increased, leading to degradation of air quality in urban centers. A study using atmospheric modeling and observational data links the worsening air quality to regional wildfire sources. The study finds that many urban centers in western US have experienced significant increases in extreme air quality episodes caused by wildfires, particularly in August and September. The results highlight the importance of regional forest management and understanding the connection between climate change, wildfire activity, and air quality.