Abstract View
Increased Photochemical Sinks Help Balance the SOA Budget: Experimental Evidence and Modeling Results
KELVIN BATES, James Cope, Tran Nguyen, Daniel Jacob, Harvard University
Abstract Number: 501
Working Group: Aerosol Chemistry
Abstract
Following the recent implementation of increased secondary organic aerosol (OA) sources, particularly from isoprene, atmospheric models tend to overestimate OA loadings. They also tend not to include photochemical sinks of OA mass, despite mounting evidence for the importance of these reactions in the atmosphere. At the same time, models frequently underestimate atmospheric loadings of small organic acids. Here, we incorporate new photochemical sinks of OA into GEOS-Chem, a global chemical transport model, and find that these chemical pathways bring simulated OA burdens into better agreement with observations from the Southeast United States and the remote troposphere. Based on recent literature, we implement photolytic OA losses with rates and photorecalcitrant fractions specific to each OA precursor; preliminary results suggest that these reactions can decrease the simulated mass of isoprene-, terpene- and aromatic-derived aerosol by up to 50%, 40%, and 18% respectively. We also implement the OH-initiated oxidation of isoprene-derived OA constituents (including 2-methyltetrols and organosulfates) based on our own bulk- and particle-phase laboratory experiments, which show that these fragmentation-dominated reactions can lead to the production and revolatilization of large yields of formic and acetic acids. We show that these pathways can reduce simulated burdens of isoprene-derived OA by up to 40% and increase the global atmospheric formic acid source by up to 23%. The incorporation of photochemical OA sinks into global models can therefore improve both OA and organic acid budgets, although the organic acids remain underestimated in GEOS-Chem.