Generation of More Potent Components at Higher Temperatures Offsets Toxicity Reduction despite Reduced Mass Emissions during Biomass Burning

Biomass burning organic aerosols (BBOAs) represent a major global health hazard. Their toxicity varies significantly due to the diversity of combustion conditions, which shape mixtures of components with differing toxic potency. We quantified component-specific contributions to intracellular reactive oxygen species generation in human bronchial epithelial cells exposed to BBOAs produced under controlled combustion conditions. Elevated combustion temperatures substantially reduced organic carbon (OC) mass emissions (by 20-fold) but resulted in a more modest reduction in OC toxicity emissions (by 5-fold). The toxicity emission reduction was primarily attributed to water-extractable OC (WOC), while methanol-extractable OC (MOC) limited this effect. The reduced emission of WOC toxicity was driven by the decreased mass emission of polar compounds such as methoxylates, as the toxicity per unit mass of WOC showed negligible changes across temperatures. In contrast, the toxicity per unit mass of MOC increased 10-fold from low to high temperatures, partially due to the formation of more potent aromatic derivatives, despite their smaller mass contribution. These findings underscore the importance of identifying key toxicity drivers to guide targeted source apportionment and refine strategies for reducing toxic emissions.