NO3-initiated secondary organic aerosol (SOA) production and NOy chemistry in a pine forest (BEACHON-RoMBAS 2011)
Speaker: Juliane Fry, Reed College, Portland, Oregon
When: Wednesday, March 14, 2012, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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Biogenic hydrocarbons, such as monoterpenes (C10) and sesquiterpenes (C15), react rapidly with nitrate radical (NO3) to form low-volatility products. We hypothesize therefore that nitrate oxidation may be an important source of secondary organic aerosol in pollution-impacted forest environments. Ambient measurements of NOy (NO2, peroxy- and alkyl-nitrates, and the gas/aerosol partitioning of the latter) and Potential Aerosol Mass measurements of NO3-initiated secondary organic aerosol formation in a 15 L flow-through reactor were made during the BEACHON-RoMBAS field campaign in U.S. Forest Service Manitou Forest Observatory, Colorado (July-August 2011). A cavity ringdown spectrometer (CRDS) is used to monitor NO3 and N2O5, Thermal Desorption - Laser Induced Fluorescence (TD-LIF) is used to detect the NOy species as NO2; an Aerodyne Aerosol Mass Spectrometer (AMS) monitors chemical composition of aerosol; Proton Transfer Reaction Mass Spectrometry (PTR-MS) monitors the gas-phase organic compounds; and a thermal converter/chemiluminescent NO/NOx/NH3 analyzer monitors gas-phase inorganic nitrogen compounds. With this suite of measurements we seek to elucidate the role of nitrate radical in biogenic SOA formation, as well as the fate of NOy in a forest environment. We observe significant concentrations of ambient alkyl- and peroxynitrates, despite the remote forest location, with peak aerosol organic nitrate concentrations observed at night. Regional and box models and laboratory chamber experiments are applied to interpret field observations.