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Secondary Organic Aerosol Formation from in situ Cl Oxidation of Ambient Air in an Oil and Gas Production Region Using an Oxidation Flow Reactor
NIRVAN BHATTACHARYYA, Catherine Masoud, Kristi McPherson, Kanan Patel, Leif Jahn, Pearl Abue, Daniel C. Blomdahl, Anita Avery, William Brune, Pawel K. Misztal, Andrew Lambe, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 355
Working Group: Aerosol Chemistry
Abstract
Karnes City, TX lies in the middle of the Eagle Ford Shale play, an oil and gas region which significantly increased production in the past decade. Previous work in the region indicated high concentrations of alkanes, alkenes, and aromatic hydrocarbons and significant local concern about air quality impacts of well heads, hydraulic fracturing fluid, and flaring. Spring 2021 fieldwork was conducted in Karnes City to examine ambient particulate matter, gas phase emissions, and atmospheric processing of these emissions. A novel oxidation flow reactor (OFR) was deployed to study in situ Cl-initiated VOC oxidation and SOA formation. Cl generated by photolysis of oxalyl chloride with low pressure mercury lamps (λ = 254 or 313 nm) reacted with ambient gases and particles over a few minutes’ OFR residence time. Ambient and post-OFR particle size distributions were assessed with a Scanning Electrical Mobility System and gas and particle phase compositions were analyzed by a variety of advanced mass spectrometry instruments including an aerosol chemical speciation monitor, a Filter Inlet for Gases and Aerosols coupled to an iodide-mode chemical ionization mass spectrometer, and a Vocus 2R proton transfer reaction mass spectrometer. During typical ambient conditions, Cl oxidation of ambient VOCs (including C6-C10 hydrocarbons measured with Vocus) resulted in formation of oxygenated VOCs (OVOC) and a 5 to 10 fold enhancement in nucleation and Aitken mode particle number concentrations. During episodic pollution events with elevated hydrocarbon emissions (e.g. nighttime flares), OFR sampling resulted in 15 to 100 fold enhancements in particle number concentration and 5 to 30 fold enhancements in organic aerosol mass. These results highlight the potential impacts of Cl-initiated oxidative aging on OVOC and SOA formation in source regions influenced by chlorine chemistry.