Chemical Transformations of Infiltrated Wildfire Smoke on Indoor-Relevant Surfaces

Indoor environments are affected during wildfire events due to the infiltration of smoke. In this study, the fate of wildfire smoke, including gases and particles, on indoor surfaces was investigated through laboratory and field experiments. Fresh smoke was generated from the burning of ponderosa pine woodchips, which produced well-established wildfire and biomass burning tracers, such as levoglucosan, 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), and 5-hydroxymethylfurfural. The interactions of smoke particles and gases were observed on different indoor-relevant building material surfaces, including glass (windows), rutile (paint and self-cleaning surfaces), and kaolinite (cement proxy and clay). However, the relative abundance of surface-bound species varied depending on the nature of these surfaces, suggesting that preferential adsorption of volatile species and particle deposition onto relevant surfaces play a key role in indoor chemistry and indoor air quality following smoke intrusion. Kaolinite surfaces, in particular, exhibited the formation of surface-initiated products during fresh smoke exposure. Furthermore, the formation of larger particles on a rutile surface was observed following ozone-aged smoke exposure, potentially resulting from the interaction of secondary organic aerosol formed during ozonolysis. Overall, this study demonstrates that different indoor-relevant material surfaces interact uniquely with smoke compounds, leading to distinct chemical transformations.