What is it?
The fraction of a county's fine particulate matter exposure that comes specifically from wildfire smoke. EPA classifies wildfire smoke as 'exceptional events' and excludes it from official air quality monitoring; the Stanford Childs/Burke dataset fills that gap.
Why it matters
Wildfire smoke now drives more PM2.5 exposure than industrial pollution in much of the western U.S. and is increasingly reaching the Midwest and Northeast. Short bursts of high smoke exposure cause asthma attacks and heart events; chronic exposure is associated with the same long-term harms as conventional PM2.5.
Reference value
Counties with more than 5 days per year of smoke-day PM2.5 above 35 µg/m³ are in a meaningfully elevated risk band.
Related health outcomes
- Asthma
- COPD
- Heart disease
Data source
Stanford Childs/Burke wildfire-attributable PM2.5 dataset · View source →