AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Enhanced Formation of Isoprene-derived Organic Aerosol in Sulfur-rich Power Plant Plumes during Southeast Nexus (SENEX)
LU XU, Ann M. Middlebrook, Jin Liao, Joost de Gouw, Hongyu Guo, Rodney J. Weber, Athanasios Nenes, Felipe Lopez-Hilfiker, Ben H. Lee, Joel A. Thornton, Charles Brock, J. Andrew Neuman, John B. Nowak, Ilana Pollack, Andre Welti, Martin Graus, Carsten Warneke, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 129 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Isoprene is the most abundant non-methane hydrocarbon emitted from vegetation. The oxidation of isoprene via RO2+HO2 pathway produces isoprene epoxydiols (IEPOX), which can uptake to acidic aqueous particles and produce secondary organic aerosol (i.e., denoted as isoprene-OA). We have observed a strong association between isoprene-OA and sulfate from ground measurements at the SOAS campaign. This association suggests that sulfate plays a critical role in isoprene-OA formation. However, mechanisms of the sulfate control on isoprene-OA formation is unclear, owing to the convoluted relationships between particle acidity, particle water, and sulfate.
In this study, we examine the effects of sulfate on isoprene-OA formation through airborne measurements in the southeastern United States during the Southeast Nexus (SENEX) field campaign. We sampled downwind from two power plants (i.e., Harllee Branch and Scherer) in Georgia. Harllee Branch emitted more sulfur dioxide (SO2) than Scherer and more aerosol sulfate was produced downwind. Interestingly, isoprene-OA formation was only enhanced in Harllee Branch plume, but not in Scherer plume. The contrast between two power plants provides an opportunity to examine the magnitude and mechanisms of sulfate on isoprene-OA formation. Isoprene-OA is estimated to decrease by 0.23±0.08 µg sm-3 with 1 µg sm-3 reduction in sulfate. Based on a parameterization of IEPOX reactive uptake, we find that sulfate enhances IEPOX uptake to particles and subsequent aqueous-phase reactions in the power plant plume, by enhancing both particle surface area and particle acidity, respectively. Finally, we use these findings to explain the observed relationships between isoprene-OA, sulfate, particle acidity, and particle water in previous studies.