AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
SOA Derived from Isoprene Epoxydiols: Insights into Formation, Aging and Distribution over the Continental US from the DC3 and SEAC4RS Campaigns
PEDRO CAMPUZANO-JOST, Brett Palm, Weiwei Hu, Douglas Day, Amber Ortega, Jose-Luis Jimenez, Jin Liao, Karl D. Froyd, Ilana Pollack, Jeff Peischl, Thomas Ryerson, Jason St. Clair, John Crounse, Paul Wennberg, Tomas Mikoviny, Armin Wisthaler, Luke Ziemba, Bruce Anderson, Simone Meinardi, Donald Blake, CIRES, University of Colorado, Boulder
Abstract Number: 405 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Recent field and laboratory data show substantial evidence for the importance of isoprene-derived SOA in areas with strong isoprene emissions, such as the SE US. Under low-NO conditions (<100 pptv), the key gas-phase intermediate is believed to be isoprene epoxide (IEPOX), which can be incorporated into the aerosol phase by sulfate ester formation (IEPOX sulfate), direct hydrolysis, or other mechanisms. SOA formed by this mechanism (IEPOX-SOA) has a characteristic fragmentation pattern when analyzed by an Aerodyne Aerosol Mass Spectrometer (AMS) with an enhanced relative abundance of the C5H6O+ ion. Using Positive Matrix Factorization (PMF) we have extracted and identified IEPOX-SOA factors for the all the AMS datasets recorded on flights on the NASA DC8 during the DC3 and SEAC4RS campaigns. These campaigns both sampled the SE US over the Spring of 2012 and the Summer of 2013, respectively
Based on this analysis, the contribution of IEPOX-SOA to total OA mass in the SE US was substantial for both DC3 and SEAC4RS flights (20-60%). IEPOX-SOA was also observed in isoprene-rich areas in the W US, albeit with smaller contributions (up to 10%). Highest concentrations of IEPOX-SOA were typically found downwind of source regions, where IEPOX is already depleted.
Main predictor for IEPOX-SOA was inorganic sulfate. At moderate aerosol water fraction a significant dependence can be observed on both total aerosol volume/surface and While organosulfates are generally not formed at higher pH/large liquid water fraction (LWC), they correlate reasonably well with IEPOX-SOA close to sources at low LWC.
IEPOX-SOA was detected up to altitudes of 5-6 km, with a somewhat different spectral pattern than the factor typically found at ground sites, This residual layer factor contributes a large amount of aerosol mass aloft, and could be due to aging of IEPOX-SOA under high RH/low ionic strength conditions at higher altitudes.