Kinetics of the Aqueous Phase Reactions of Atmospherically Relevant Monoterpene Epoxides

Laboratory and field measurements have demonstrated that an isoprene-derived epoxide intermediate (IEPOX) is the origin of a wide range of chemical species found in ambient secondary organic aerosol (SOA). In order to explore the potential relevance of a similar mechanism for the formation of monoterpene-derived SOA, nuclear magnetic resonance techniques were used to study kinetics and reaction products of the aqueous-phase reactions of several monoterpene epoxides: beta-pinene oxide, limonene oxide, and limonene dioxide. The present results, combined with a previous study of a-pinene oxide, indicate that all of these epoxides will react more quickly than IEPDX with aqueous atmospheric particles, even under low-acidity conditions. As for a-pinene oxide, the observed products can be mainly rationalized with a hydrolysis mechanism, and no long-lived organosulfate or nitrate species nor species that retain the beta-pinene bicyclic carbon backbone are observed. As bicyclic ring-retaining organosulfate and nitrate species have been previously observed in monoterpene-derived SOA, it appears that monoterpene-derived epoxides may not be as versatile as IEPDX in producing a range of SOA species, and other mechanisms are needed to rationalize organosulfate and nitrate formation.