TheInfluence of Wildfire Smoke on Ambient PM_2.5 Chemical SpeciesConcentrations in the Contiguous US

Wildfires significantly contribute to ambient air pollution, yet our understanding of how wildfire smoke influences specific chemicals and their resulting concentration in smoke remains incomplete. We combine 15 years of daily species-specific PM_2.5 concentrations from 700 air pollution monitors with satellite-derived ambient wildfire smoke PM_2.5, and use a panel regression to estimate wildfire smoke’s contribution to the concentrations of 27 different chemical species in PM_2.5. Wildfire smoke drives detectable increases in the concentration of 25 out of the 27 species with the largest increases observed for organic carbon, elemental carbon, and potassium. We find that smoke originating from wildfires that burned structures had higher concentrations of copper, lead, zinc, and nickel relative to smoke from fires that did not burn structures. Wildfire smoke is responsible for an increasing share of ambient concentrations of multiple species, some of which are particularly harmful to health. Using a risk assessment approach, we find that wildfire-induced enhancement of carcinogenic species concentrations could cause increases in population cancer risk, but these increases are very small relative to other environmental risks. We demonstrate how combining ground-monitored and satellite-derived data can be used to measure wildfire smoke’s influence on chemical concentrations and estimate population exposures at large scales.