The roles of individual oxidants in secondary organic aerosol formation from Δ3-carene: 2. soa formation and oxidant contribution

This is Part 2 of a series of papers that address the role of individual oxidants in secondary organic aerosol (SOA) formation from the oxidation of Δ3-carene. In the present paper, an equilibrium gas–particle partitioning model is developed and used in conjunction with the gas-phase chemical mechanism described in Part 1 to perform simulations of SOA formation from the oxidation of Δ3-carene in a series of ozonolysis, nitrate radical, and photooxidation experiments. Simulations of the ozonolysis, nitrate radical, and photooxidation chamber experiments indicate that the main characteristics of the chemistry and gas–particle partitioning are adequately described by the chemical mechanism and equilibrium module. Results indicate that for photooxidation experiments, while O3-initiated chemistry is required to initiate SOA formation, the hydroxyl radical is the primary oxidant contributing to hydrocarbon consumption and contributes the most to SOA mass. Although contributing less than the primary oxidants, cross-products (products that are formed via oxidation pathways that include two or more oxidants) constitute a potentially significant contribution (up to 7%) to SOA formation. New particle phase formation appears to result from products formed via ozone oxidation. The effects of varying temperature and the ratio of hydrocarbon to oxides of nitrogen (ppbC/ppb) on SOA formation and oxidant contribution are explored. A model simulation with conditions more representative of the actual ambient atmosphere indicate an increased contribution to SOA of products generated from O3-initiated oxidation as well as cross-products.