Online Measurements\nduring Simulated Atmospheric Aging\nTrack the Strongly Increasing Oxidative Potential of Complex Combustion\nAerosols Relative to Their Primary Emissions

Oxidative potential (OP) is increasingly recognized as\na more health-relevant\nmetric than particulate matter (PM) mass concentration because of\nits response to varying chemical compositions. Given the limited research\non the OP of complex combustion aerosols, the effects of aging processes\non their OP remain underexplored. We used online instruments to track\nthe evolution of OP [via dithiothreitol (DTT) assays] during the aging\nof wood burning and coal combustion emissions by hydroxyl-radical-driven\nphotooxidation and dark ozonolysis. We observed very substantial increases\nin the intrinsic OP (OP<sub>m</sub><sup>DTT</sup>) of complex combustion\naerosols (e.g., OP<sub>m</sub><sup>DTT</sup> up to 100 pmol min<sup>–1</sup> μg<sup>–1</sup> for OH-aged wood burning\nemissions) within 1 day of equivalent aging. Further analysis in relation\nto the degree of oxidation revealed a potential for generalizing the\nOP of carbonaceous aerosols with average carbon oxidation state OS̅c values ranging from −1.5 to −0.5\nby assuming they have a constant OP<sub>m</sub><sup>DTT</sup> value\nof ∼10 ± 6 pmol min<sup>–1</sup> μg<sup>–1</sup>. Additionally, we uncovered a strong dependency of OP<sub>m</sub><sup>DTT</sup> on both the source/precursor and aging pathway with OS̅c above ∼−0.5. OH photooxidation\nwas identified as an exceptionally efficient pathway for generating\nhighly oxidized, multifunctionalized, and DTT-active products, particularly\nfrom wood burning emissions.