AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Long Lifetime of Ambient Isoprene Epoxydiols-Derived Secondary Organic Aerosol (IEPOX-SOA) against OH Oxidation and Evaporation
WEIWEI HU, Brett Palm, Douglas Day, Pedro Campuzano-Jost, Jordan Krechmer, Zhe Peng, Suzane de Sá, Scot Martin, Lizabeth Alexander, Karsten Baumann, Lina Hacker, Astrid Kiendler-Scharr, Abigail Koss, Joost de Gouw, Allen H. Goldstein, Roger Seco, Steve Sjostedt, Jeong-Hoo Park, Alex Guenther, Saewung Kim, Francesco Canonaco, Andre Prévôt, William Brune, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder
Abstract Number: 92 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) can contribute substantially to organic aerosol (OA) concentrations in forested areas under low NO conditions, hence significantly influencing the regional and global OA budgets, accounting for example for 16-36% of the submicron OA in the SE US summer. Particle evaporation measurements during the Southern Oxidant and Aerosol Study (SOAS) in SE US of summer 2013 and the Green Ocean Amazon (GoAmazon2014/5) of dry season 2014 showed that ambient IEPOX-SOA likely exists mostly as oligomers. Thus it only evaporates slowly after dilution and is inaccessible to gas phase oxidation in the atmosphere. The OH aging process of ambient IEPOX-SOA was investigated with an oxidation flow reactor (OFR). The heterogeneous reaction rate coefficient of ambient IEPOX-SOA with OH radical (kOH) was estimated as 4.0 ± 2.0×10$^(-13) cm$^(3) molec$^(-1) s$^(-1), which is equivalent to more than a 2-week lifetime. A similar kOH was found for IEPOX-SOA in ambient air in the Amazon rainforest. At higher OH exposures in the reactor (>1×10$^(12) molec. cm$^(-3) s), a mass loss of IEPOX-SOA is observed, due to heterogeneous reaction and volatilization of fragmented reaction products. We report for the first time OH reactive uptake coefficients (γOH=0.59±0.33 in SE US and γOH=0.68±0.38 in Amazon) for SOA under ambient conditions. A relative humidity dependence of kOH and γOH was observed, consistent with surface area-limited OH uptake. These observation of physicochemical properties of IEPOX-SOA have important implications for ambient aerosol lifecycle and will help to constrain the impact of OA on air quality and climate.