AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effect of Particle Acidity on the Yield and Chemical Composition of Secondary Organic Aerosol from OH-Initiated Photooxidation of Alpha-Pinene under Low- and High-NO Conditions
YUEMEI HAN, John Liggio, Shao-Meng Li, Craig A. Stroud, Environment Canada
Abstract Number: 278 Working Group: Aerosol Chemistry
Abstract Atmospheric oxidation of biogenic hydrocarbons emitted from terrestrial vegetation contributes to a substantial amount of secondary organic aerosol (SOA). The production of SOA may be enhanced with increased aerosol acidity through acid-catalyzed heterogeneous reactions. However, the dependency of SOA on aerosol acidity has not been considered in most atmospheric chemistry models to date. In this study, experiments on SOA formation from OH-initiated photooxidation of alpha-pinene were performed in a photochemical reaction chamber to investigate the effect of aerosol acidity on the yield and chemical composition of SOA under low- and high-NO conditions. The concentrations of alpha-pinene and formed SOA were measured in real-time using a proton-transfer-reaction time-of-flight mass spectrometer and a high-resolution time-of-flight aerosol mass spectrometer, respectively. The SOA yields derived from the alpha-pinene photooxidation in low-NO experiments were substantially higher than those in high-NO experiments and did not vary significantly with aerosol acidity. In contrast, under high-NO conditions, the SOA yields increased with the increase of aerosol acidity, especially during the initial period of irradiation. The chemical composition of the SOA did not change substantially with the irradiation time once it was formed, which is evidenced by the minor changes of fragmentation patterns in the organic mass spectra during each experiment. The fraction of N-containing organic fragments increased with aerosol acidity under high-NO conditions, suggesting that organic nitrates may be heterogeneously reacting through a mechanism catalyzed by aerosol acidity. The dependence of the SOA yield from alpha-pinene photooxidation on aerosol acidity revealed from this study will be parameterized and utilized in a lagrangian box model equipped with a modified SAPRC-07 chemical mechanism to evaluate the significance of aerosol acidity in the real atmosphere, which is downwind of sulfur dioxide emission sources and over terrestrial vegetation.