[PAOCQ] Jessica Haskins (University of Utah)

“The Global Importance of Gas-phase Peroxy Radical Accretion Reactions for SOA Formation and Radiative Forcing”

Reactions between two gas-phase peroxy radicals (RO2), or accretion reactions, can form dimer species, representing a significant but under-investigated pathway in secondary organic aerosol (SOA) formation, with implications for both air quality and climate. This work makes use of recent advances in our theoretical chemical understanding of RO2 accretion reaction rates to assess their contribution to SOA. After evaluation in a chemical box model, a reduced representation of RO2 accretion reactions was added to GEOS-Chem to assess their contribution to global SOA concentrations and their associated radiative impact. Our results suggest that RO2 accretion products comprise 30–50% of particulate matter (PM2.5) in tropical forested environments, and a smaller proportion in more temperate regions like the south-eastern USA (≈5 %). This work confirms that biogenic volatile organic compounds (BVOCs) are the main precursors to accretion products globally, but suggests that a notable fraction of aerosol-phase accretion products come from aromatic-derived RO2 and small acyl-peroxy radicals. Contrary to previous assumptions that accretion products are organic peroxides, our box modeling investigation suggests that non-peroxide accretion products (ethers and esters) could comprise the majority of accretion products in both the gas and aerosol phase. This work provides justification for more extensive measurements of RO2 accretion reactions in laboratory experiments and RO2 accretion products in the ambient atmosphere in order to better constrain the representation of this chemistry in atmospheric models, including a greater level of mechanistic chemical representation of SOA formation processes.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

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