Volatile Organic Compounds Inside Homes Impacted by Smoke from the Marshall Fire

Wildfires at the wildland–urban interface (WUI) have been increasing in frequency over recent decades due to increased human development and shifting climatic patterns. The work presented here focuses on the impacts of a WUI fire on indoor air using field measurements of volatile organic compounds (VOCs) by Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). We found a slow decrease in VOC mixing ratios over the course of roughly 5 weeks starting 10 days after the fire, and those levels decreased to ∼20% of the initial indoor value on average. The VOC composition could be described by a combination of biomass burning emissions and indoor air composition. Comparisons were made between polycyclic aromatic hydrocarbon (PAH) distributions in the gas phase and ash, with differences observed in their distribution between each other and when compared to fresh fuel inventory measurements. Mitigation tests were conducted running air cleaners with activated carbon and opening windows to promote indoor–outdoor air exchange, with both methods showing a decrease greater than 50% for average VOC levels indoors while active. We compare our results with simulated smoke impact experiments that show the slow decline in VOCs must be understood in the context of indoor reservoirs, beyond just on surfaces, leading to the slow release of VOCs to indoor air.