The roles of individual oxidants in secondary organic aerosol formation from Δ3-carene:: 1.: gas-phase chemical mechanism

Oxidation of certain gas-phase organic species results in secondary products of volatility that is sufficiently low that they partition between the gas and aerosol phases. The fraction that partitions to the aerosol phase is known as secondary organic aerosol (SOA). The present paper reviews the relevant chemistry and describes the development of a chemical mechanism that consists of the gas-phase reactions of Delta(3)-carene and its products, including the formation of individual organic oxidation products that are capable of forming SOA. The mechanism also incorporates ozone formation chemistry and other relevant inorganic reactions. The new mechanism differentiates specific oxidation products according to both molecular structure and routes of formation. The concentrations of oxidation products (termed cross-products) that are formed in pathways involving two or more oxidants (ozone, the oxygen atom, and the hydroxyl and nitrate radicals) are accurately accounted in this way. The mechanism is evaluated in a zero-dimensional model by simulating gas-phase concentrations of Delta(3)-carene, oxides of nitrogen, and ozone from ozonolysis, nitrate radical, and photooxidation chamber experiments in which Delta(3)-carene was oxidized. Simulation results indicate that the main characteristics of the chemistry are adequately described by the mechanism. Part 2 of this series of papers develops a gas-particle partitioning model and presents simulations of SOA formation in single oxidant (e.g., ozonolysis and nitrate radical) and photooxidation experiments. Part 2 examines in detail the role of individual oxidants in consumption of the parent organic, creation of cross-products, and formation of SOA. (C) 2004 Elsevier Ltd. All rights reserved.