AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Understanding Missing Sources of Fine Particulate Organosulfur Compounds in the Southeastern US: Implications from Ambient Measurements and Laboratory Experiments
YUZHI CHEN, Matthieu Riva, Karsten Baumann, Tianqu Cui, Mike Fort, Eric Edgerton, Lindsay Yee, Weiwei Hu, Sri Hapsari Budisulistiorini, Caitlin Rose, Zhenfa Zhang, Allen H. Goldstein, Jose-Luis Jimenez, Stephanie L. Shaw, Avram Gold, Jason Surratt, University of North Carolina at Chapel Hill
Abstract Number: 793 Working Group: Aerosol Chemistry
Abstract Organosulfates (OSs) can contribute a substantial mass fraction of total organic aerosol (OA), and presumably, fine particulate organosulfur. Multiphase chemical processes have been demonstrated to form OSs, such as from the reactive uptake of certain oxidation products from biogenic volatile organic compounds (BVOCs) onto acidic sulfate aerosols. As sulfate over continental regions is generally of anthropogenic origin, it is important to assess its influence on biogenic secondary organic aerosol formation. Chemical analyses were performed on PM2.5 collected during the 2013 Southeast Oxidant and Aerosol Study at the SEARCH Centreville, Alabama ground site. OSs and methanesulfonic acid (MSA) were characterized and quantified by ultra-performance liquid chromatography interfaced to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS). Total organosulfur mass was determined by isotope ratio inductively coupled plasma mass spectrometry. While the sum of 33 OSs and MSA contributes to 8% of total OA, it only explains 50% of the total organosulfur mass, suggesting significant missing organosulfur sources. We hypothesized that the multiphase chemistry of BVOC oxidation products with acidic sulfate aerosols produces previously unidentified oligomers containing sulfate. Aiming to investigate the missing sources, follow-up chamber experiments were conducted using acidic sulfate aerosols to generate isoprene-derived SOA. Inorganic and organic sulfates were characterized and quantified by a particle-into-liquid sampler coupled to offline ion chromatography and UPLC/ESI-HR-QTOFMS. Real-time measurement techniques were also used to track the reaction dynamics in both gas and particle phase. If sulfur mass closure can be achieved for the chamber experiments, it will help us interpret our findings on ambient organosulfur. Results from this study will direct future investigations to achieve mass closure for ambient organosulfur, helping to improve model predictions of PM2.5 in the southeastern US.