Seminar

Abstract

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.