The Impacts of NOx on the Composition, Volatility, and Aging Characteristics of Biogenic and Anthropogenic Secondary Organic Aerosol

Description

Organic material comprises 20 to 90% of total submicron particle mass in the atmosphere, a majority of which is formed from the gas-to-particle conversion of volatile organic compound (VOC) oxidation products as secondary organic aerosol (SOA). The evolution of SOA particles is not well-understood, and models cannot predict the magnitude of atmospheric SOA concentrations with either lab-based parameterizations or explicit chemical models. In a collaboration between the University of Washington and the Pacific Northwest National Laboratory, experiments in an environmental simulation chamber probed the lifecycle of SOA formed from both biogenic and anthropogenic VOC precursors using a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) coupled with the Filter Inlet for Gases and Aerosols (FIGAERO), a proton-transfer-reaction mass spectrometer (PTR-MS), and an aerosol mass spectrometer (AMS). The VOC precursors were oxidized in batch mode under a variety of photochemical conditions involving hydroxyl radicals and ozone with and without NOx to assess the impact of NOx on the SOA lifecycle. We measured distinct molecular composition profiles and volatility for each SOA system, and these properties evolved substantially upon subsequent aging. We utilize the differing evolution of SOA molecular composition and volatility with NOx and aging to interpret the importance of various pathways to regional SOA as measured in two different field campaigns.