AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Role of Morphology on the Rate and Products of Heterogeneous Oxidation of Organic Aerosol
REBECCA SUGRUE, Christopher Lim, Martin Wolf, Daniel Cziczo, Jesse Kroll, MIT
Abstract Number: 353 Working Group: Aerosol Chemistry
Abstract Heterogeneous oxidation of organic aerosol (OA) by hydroxyl radicals can affect particle mass and composition over long atmospheric timescales (several days to weeks of atmospheric oxidation). However, previous studies on heterogeneous oxidation have for the most part used pure, organic particles, which may not be representative of ambient aerosols. In order to study the role of particle morphology on oxidation kinetics and mechanisms, we carried out a series of heterogeneous oxidation experiments on thin organic coatings. Ammonium sulfate particles were passed through a squalane reservoir to condense a thin (1-10 nm) layer of squalane (C30H62) on the seed particles then photochemically oxidized by exposure to hydroxyl radicals (OH) in a flow tube reactor. Oxidation kinetics and products were measured using an AMS and organic mass was measured using an SMPS and AMS PToF data; in addition, CCN activity of the oxidized particles was monitored. Coated aerosols underwent large changes in carbon oxidation state and CCN activity after relatively short atmospheric aging times (the equivalent of 1-3 days in the atmosphere), due to the high surface-area-to-volume ratios of the organic coatings. This work indicates that heterogeneous oxidation may change the chemical composition and properties of morphologically complex OA particles at a significantly faster rate than is currently assumed.