Wildfires and wood stoves: Woodsmoke toxicity and chemical characterization study in the north-western United States

Abstract

PM2.5 is the most monitored air pollutant for which EPA has set national ambient air quality standards (NAAQS). As such, it is the pollutant on which the Air Quality Index (AQI) is most often based. PM2.5 and PM10 are the only criteria pollutant whose composition, and therefore toxicity varies. The PM2.5 AQI does not account for chemical composition. In areas where woodsmoke is the dominant PM2.5 source, coemitted hazardous air pollutants (HAPs) could impact community health differently than indicated by PM2.5 based AQI. PM2.5, carbon monoxide (CO), and particle light absorption were measured continuously from August 2018 through May 2019 in a suburban community where woodsmoke contributed the majority of ambient PM2.5. Air samples were also collected at least every 6 days at the site and analyzed for a suite of hazardous air pollutants (HAPs). EPA's positive matrix factorization (PMF) model 5.0 was used to identify the primary source contributors to local air pollution and apportion what fraction of each pollutant was from woodsmoke. Both measurements and the PMF model result showed significant chemical distinction between wood stove and wildfire smoke. Wildfire smoke contained significantly less CO and organic compounds than wood stove smoke relative to measured PM2.5. Comparing select HAPs to ambient CO concentration indicated atmospheric oxidation depleted PAHs in the wildfire smoke, although the relative amount of UV absorbing organic carbon did not change. HAPs most strongly associated with wood combustion were assessed relative to their individual cancerous and non-cancerous screening levels, as well as the PM2.5 and CO NAAQS.