Production of SOA from Hydroxyl Radical Oxidation of Two Cyanobacterial-derived BVOCs, Geosmin and 2-Methylisoborneol

HALEY E. PLAAS, Jin Yan, N. Cazimir Armstrong, Hans W. Paerl, Jason Surratt, UNC Chapel Hill

     Abstract Number: 209
     Working Group: Aerosol Sources and Constituents of Emerging Importance and Their Impacts across Spatial Scales

Abstract
Several studies have examined the production, transport, and atmospheric fate of biogenic volatile organic compounds (BVOCs) emitted from marine phytoplankton, but BVOCs produced by freshwater algae are largely overlooked. Particularly, bloom-forming, harmful cyanobacteria are known to produce a suite of volatile metabolites, including geosmin (GSM) and 2-methlyisoborneol (2-MIB), an irregular sesquiterpene and monoterpene, respectively. GSM and 2-MIB are commonly tested for in water supplies, but their fate in the atmosphere is unknown. Hydroxyl radicals (·OH) are one key atmospheric oxidant which react rapidly with VOCs to form secondary gases and organic aerosols, which impact climate and human health. To investigate this pathway, we oxidated both GSM and 2-MIB via ·OH and observed the size distribution, concentration, and chemical composition of the secondary organic aerosol (SOA) produced. In separate triplicate trials, GSM and 2-MIB reacted with ·OH at a relative humidity of 50% in a Potential Aerosol Mass Oxidative Flow Reactor (PAM-OFR) for 30-38 days of equivalent atmospheric ·OH exposure. Conditions in the PAM were selected to mimic conditions in the southeastern United States during summertime when cyanobacterial blooms are most common. Real-time particle mass and number concentrations were measured using a scanning mobility particle sizer, and nucleation events were observed following the oxidation of both cyanobacterial-derived BVOCs, with mass concentrations of ~80 µg m^-3 for GSM and ~200 µg m^-3 for 2-MIB. SOA chemical composition was measured by impacting particles onto a Teflon filter for offline analysis using reverse phase liquid chromatography coupled with electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (RPLC/ESI-HR-QTOFMS). Filters are currently being analyzed for chemical constituents of SOA produced and SOA formation pathways are being proposed. We anticipate the molecular-level SOA constituents identified may serve a potential chemical tracers needed for source apportionment of SOA particles derived from harmful cyanobacteria in freshwater systems.