Assessing Wildfire Impact on Diffusive Flux of Parent and Alkylated PAHs: A Pilot Study of Soil-Air Chemical Movement before, during, and after Wildfires.

The global wildfire risk is predicted to rise due to contributing factors of historical fire management strategies and increases in extreme weather conditions. Thus, there is a need to better understand contaminant movement and human exposure to wildfire smoke. Vapor-phase polycyclic aromatic hydrocarbons (PAHs) are elevated during wildfires, but little is known about how these chemicals move during and after wildfire events for exposure risk assessment. Paired air and soil pore air passive samplers were deployed before, during, and after wildfires to determine diffusive flux of vapor-phase parent (p-PAH) and alkylated (a-PAH) PAHs in the Western United States. Naphthalene and 2-methylnaphthalene contributed to most of the volatilization and deposition (6.3-89%) before and after a wildfire. Retene (41%) and phenanthrene (27%) contributed substantially to deposition during a wildfire. During wildfires, the number of PAHs in deposition increased at sites with worse air quality. Most p-PAHs and a-PAHs were either depositing or near equilibrium after a wildfire, except for retene at several locations. A majority (≥50%) of PAHs had a 50% magnitude difference between flux before and after a wildfire. This study increases the understanding of PAH movement and exposure during each stage of the wildfire cycle.