Global-scale analysis of the effect of gas-phase Criegee intermediates (CIs) to the sulphate aerosol formation: General trend and the importance of hydroxy radical decomposed from vibrationally-excited CIs

Abstract

Stabilised Criegee intermediates (sCIs), which are formed in the atmosphere through the ozonolysis of alkenes, are known precursors of sulphate aerosols (SO42-(p)). Several previous studies have focused on the kinetics of sCI-related chemistry using both experimental and theoretical methods. Nonetheless, detailed evaluations of how the sCI affects global-scale SO42-(p) formation using chemical transport models (CTMs) have rarely been conducted. In this study, the impact of sCIs on SO42-(p) and other particulate matter was estimated using a global CTM by implementing approximately 100 chemical reactions associated with CIs-chemistry. The results suggest that sCIs contribute maximally less than 0.5% in remote areas, such as Amazon rainforests, middle Africa, and Australia. This value is lower than the previously estimated value. The sCI that contributed the most to SO42-(p) formation was E-methyl glyoxal-1-oxide, which is generated by the ozonolysis of methyl vinyl ketone owing to its low-rate constant for the loss reaction of unimolecular decomposition and water vapour. The change in SO42-(p) enhanced the formation of secondary organic aerosol, whereas the reactions of the sCIs and NO2 degraded the formation of nitrate radicals. The results of the sensitivity analyses showed that in highly industrialised sites in China and India, OH radicals formed by the unimolecular decomposition of vibrationally excited CIs (vCIs) contributed to SO42-(p) formation, which maximally accounted for nearly ten times more than that of sCIs, whereas the importance of vCIs and sCIs to SO42-(p) formation were estimated to be almost equal in rural and remote sites. The estimated sCI loss by HNO3 and organic acids was comparable to that of the unimolecular decomposition of sCIs and scavenging by water. This study provides full insight into the impact of gas-phase CIs chemistry on the global-scale atmosphere.