Hazardous Air Pollutants in Fresh and Aged Western US Wildfire Smoke and Implications for Long-Term Exposure

Abstract

Wildfires have a significant adverse impact on air quality in the United States (US). To understand the potential health impacts of wildfire smoke, many epidemiology studies rely on concentrations of fine particulate matter (PM) as a smoke tracer. However, there are many gas-phase hazardous air pollutants (HAPs) identified by the Environmental Protection Agency (EPA) that are also present in wildfire smoke plumes. Using observations from the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN), a 2018 aircraft-based field campaign that measured HAPs and PM in western US wildfire smoke plumes, we identify the relationships between HAPs and associated health risks, PM, and smoke age. We find the ratios between acute, chronic noncancer, and chronic cancer HAPs health risk and PM in smoke decrease as a function of smoke age by up to 72% from fresh (<1 day of aging) to old (>3 days of aging) smoke. We show that acrolein, formaldehyde, benzene, and hydrogen cyanide are the dominant contributors to gas-phase HAPs risk in smoke plumes. Finally, we use ratios of HAPs to PM along with annual average smoke-specific PM to estimate current and potential future smoke HAPs risks.

Daytime Oxidized Reactive Nitrogen Partitioning in Western U.S. Wildfire Smoke Plumes

“…Furthermore, O'Dell et al. (2020) found general agreement between this chemical age categorization and physical age estimates of fresh smoke plumes samples during WE‐CAN. Thus, age uncertainties are unlikely to significantly impact our conclusions.…”

Seasonality and Source Apportionment of Nonmethane Volatile Organic Compounds at Boulder Reservoir, Colorado, Between 2017 and 2019

“…Based on the emissions and lifetime (e.g., at least a day), we would expect elevated levels of hydrogen cyanide, acetone, acetonitrile, and methyl ethyl ketone during smoke‐impacted periods (Akagi et al., 2012), although these species were not quantified by the instrument system used in this study. Some species that are both emitted and produced in smoke (e.g., acetaldehyde and formaldehyde) would also be present in aged smoke (O'Dell et al., 2020), but these species are also not available for this analysis. When a 7th factor is included in the PMF model to represent an additional source contribution from smoke in the entire summer dataset and the resultant 7‐factor solution is compared with the 6‐factor smoke‐free PMF solution, the results show that there is little difference in the percent contributions from each of the six nonsmoke factors to the observed NMVOC mixing ratios.…”

Empirical Insights Into the Fate of Ammonia in Western U.S. Wildfire Smoke Plumes

“…We also assigned a broader set of smoke plume intercepts an approximate chemical age following O'Dell et al. (2020). This assignment of chemical age is useful because it allows us to examine the partitioning of NH x in all the smoke samples intercepted during WE‐CAN, not just those that were sampled in a pseudo‐lagrangian fashion from known fires.…”