Estimating the Formation of Secondary Organic Aerosol under Controlled Atmospheric Conditions
YANYU ZHANG, David R. Cocker III, University of California, Riverside
Abstract Number: 42
Working Group: Aerosol Chemistry
Abstract
Secondary Organic Aerosol (SOA) plays an essential role in air quality, climate, and human health. Oxidation of both anthropogenic and biogenic sources of Volatile Organic Compounds (VOCs) contribute to SOA formation. Traditional chamber experiments provide limited insight as they typically estimate SOA formation from a single precursor whose reactive chemistry (e.g., OH/HO2, NO/NO2, O3, etc.) is controlled by the oxidation processes of the single precursor itself. However, the real atmosphere consists of not just the single SOA precursors but also a complex mixture of organic compounds that control the reactive chemistry, making accurate prediction of SOA formation from a single precursor experiment difficult. In this study, environmental chamber experiments were conducted in the 120 m3 environmental chamber at University of California Riverside Atmospheric Processes Laboratory (APL). Surrogates (defined mixtures of Reactive Organic Gases (ROGs)) were added to a series of single precursor environmental chamber simulations to fix atmospheric reactivity and further our understanding of SOA formation from selected precursors, like α-pinene, m-xylene, etc. Two groups of surrogate mixture of ROGs were selected to represent the reactivity of an anthropogenic urban atmosphere (e.g., Los Angeles) and a strong biogenic-influenced urban atmosphere (e.g., Atlanta). With the surrogates introduced, the pathway of the gas mechanism is controlled by the oxidation chemistry, primarily associated with the surrogate mixture and with little influence from the test compound itself. The experiments demonstrate that the concentration of gas phase species is heavily affected by the surrogates instead of the added precursor, whereas the aerosol physical and chemical properties are heavily affected by the added precursor. Our work enables the development of incremental aerosol formation scales for anthropogenic and biogenic surrogate systems, and improve our understanding of different factors that contribute to SOA formation.