Unexpected electrophiles in the atmosphere - anhydride nucleophile reactions and uptake to biomass burning emissions.

Biomass burning is a significant contributor to atmospheric pollution, its emissions have been found to have adverse impacts on climate and human health. Largely, these impacts are dictated by how the composition of the emissions changes once emitted into the atmosphere. Recently, anhydrides have been identified as a significant fraction of biomass burning emissions, however, little is known about their atmospheric evolution, or their interactions within the burn plume. Without this understanding, it is challenging to predict the impact of anhydrides on biomass burning emissions, and by extension, their influence on climate and health. In this study, we investigate anhydrides as potentially unrecognized electrophiles in the atmosphere. Firstly, by exploring their reactivity towards important biomass burning emitted nucleophiles, and secondly, by measuring their uptake on the emissions themselves. Our results show that phthalic and maleic anhydride can react with a wide range of nucleophiles, including hydroxy and amino-containing compounds, such as levoglucosan or aniline. Additionally, using a coated-wall flow tube setup, we demonstrate that anhydrides reactively uptake to biomass burning films and influence their composition. The anhydride nucleophile reaction was found to be irreversible, proceeding without sunlight or free radicals and indicating it may occur during the day or nighttime. Furthermore, the reaction products were found to be water-stable and contain functional groups which enhance their mass and likely contribute to the formation of secondary organic aerosol, with knock-on climate effects. Overall, our study sheds light on the fundamental chemistry of anhydrides and their potential impacts in the atmosphere.