PNNL

Abstract

Oxidation of the monoterpene ?3-carene (C10H16) is a potentially important and under-studied source of atmospheric secondary organic aerosol (SOA). We present chamber-based measurements of the speciated gas and particle phases during photochemical oxidation of ?3-carene. We find evidence of highly oxidized organic molecules (HOM) in the gas phase and relatively low volatility SOA dominated by C7-C10 species. We then use computational methods to predict rate coefficients of likely autoxidation and bond scission reactions to develop the first stages of a ?3 -carene photochemical oxidation mechanism and explain some of our measured compositions. We find that alkoxy bond scission of the cyclohexyl ring likely leads to efficient HOM formation, inline with previous studies. We also find a surprising role for the unimolecular alkoxy radical abstraction of primary hydrogens from methyl groups, which has been calculated to be rapid in the a-pinene system, and suggest more research is required to determine if this is more general to other systems and a feature of autoxidation. This work develops the most comprehensive view to-date of ?3-carene photochemical oxidation products via measurements and lays out a suggested mechanism of oxidation via computationally derived rate coefficients.