Photosensitized Decay of Levoglucosan in Biomass Burning Aerosol Particles

Biomass burning (BB) is increasingly relevant to air quality as global warming intensifies wildfire activity. Levoglucosan (LEVO) is a widely used tracer for BB, but its oxidative decay is still less understood. While gas-phase hydroxyl radicals (•OH) have been considered the primary oxidants for LEVO decay in biomass burning organic aerosol (BBOA) particles, high particulate viscosity at low relative humidity (RH) limits •OH uptake. In this study, we demonstrate a less recognized pathway that leads to LEVO degradation in BBOA particles under light, which is primarily driven by triplet excited states (3BBOA*) via hydrogen transfer in photosensitization reactions. Unlike •OH oxidation that relies on mass transfer of oxidants from the gas phase, 3BBOA* oxidation remains effective in viscous particles at low RH and accounts for ∼50% of LEVO decay, shortening its chemical lifetime in previous estimates by a half to ∼1.8 days. These findings highlight the importance of processes that generate oxidants within particles, such as photosensitization, and enhance our understanding of the atmospheric fate of LEVO to facilitate BB tracking.