Polycyclic Aromatic Hydrocarbons (PAHs) in Wildfire Smoke Accumulate on Indoor Materials and Create Postsmoke Event Exposure Pathways

Abstract

Wildfire smoke contains PAHs that, after infiltrating indoors, accumulate on indoor materials through particle deposition and partitioning from air. We report the magnitude and persistence of select surface associated PAHs on three common indoor materials: glass, cotton, and mechanical air filter media. Materials were loaded with PAHs through both spiking with standards and exposure to a wildfire smoke proxy. Loaded materials were aged indoors over ∼4 months to determine PAH persistence. For materials spiked with standards, total PAH decay rates were 0.010 ± 0.002, 0.025 ± 0.005, and 0.051 ± 0.009 day–1, for mechanical air filter media, glass, and cotton, respectively. PAH decay on smoke-exposed samples is consistent with that predicated by decay constants from spiked materials. Decay curves of smoke loaded samples show that PAH surface concentrations are elevated above background for ∼40 days after the smoke clears. Cleaning processes efficiently remove PAHs, with reductions of 71% and 62% after cleaning smoke-exposed glass with ethanol and a commercial cleaner, respectively. Laundering smoke-exposed cotton in a washing machine and heated drying removed 48% of PAHs. An exposure assessment indicates that both inhalation and dermal PAH exposure pathways may be relevant following wildfire smoke events.

Indoor–Outdoor Oxidative Potential of PM2.5 in Wintertime Fairbanks, Alaska: Impact of Air Infiltration and Indoor Activities

“…The long sample time of these OP DTT data limits a more detailed investigation of the repartitioning of the DTT-active species. We speculate this partitioning would be mainly from pellet stove emissions adsorbing to indoor surfaces, providing a reservoir for subsequent re-emission . From these data, we cannot conclude that there is a definitive effect.…”

“…We speculate this partitioning would be mainly from pellet stove emissions adsorbing to indoor surfaces, providing a reservoir for subsequent re-emission. 71 From these data, we cannot conclude that there is a definitive effect. In the further analysis below, given the substantial variability in OP DTT observed during the No-experiment period, the pollutant enhancements and PM 2.5 OP DTT in perturbation experiments were exclusively compared to the Background levels.…”

After the Smoke Clears: Wildland–Urban Interface Fires and Residues in Nearby Homes

“…Then the materials aged, sitting indoors for 4 months as the scientists regularly measured levels of a class of semi-volatile PAHs associated with wildfire smoke. Gall says one reason the study 30 focused on this class of PAHs and not VOCs is because their lower volatility meant they were more likely to stick to indoor surfaces.…”

“…He and his coauthors found that elevated levels of these PAHs lasted for roughly 40 days on the samples but were lowered dramatically by simple cleaning steps, like using glass cleaner and laundering the fabric. 30 Again, the concern was with surfaces more difficult to clean because these PAHs may also stick to—or even potentially bond with—other household surfaces, 31 he says, such as carpet or drywall. People may then be exposed through inhalation when PAHs revolatilize, or through skin contact, as may happen when an infant crawls on a carpet.…”

“…In the United States, federal agencies 40 , 41 are currently funding laboratory studies to better understand the chemical compounds that come from burning material. Some research, like that of de Gouw and Gall, 30 involves combusting small amounts of building materials. Other studies will focus on materials combustion at larger scale.…”