Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

Significance Ozonolysis is an important sink of alkenes in Earth’s troposphere, leading to the formation of Criegee intermediates (CIs), whose reactions significantly impact tropospheric composition. The reactivity of the four-carbon unsaturated CIs derived from isoprene, the most abundant alkene, has remained unknown until now. Direct measurements of one such CI, methyl vinyl ketone oxide (MVK-oxide), with water vapor, SO 2 , and formic acid are reported herein, substantiated by high-level theory, revealing the long lifetime of syn- MVK-oxide with respect to unimolecular decay and reaction with water vapor. Through a combination of direct experiment, high-level theory, and global modelling, syn -MVK-oxide is shown to survive high-humidity tropospheric environments and play a role in sulfuric acid formation and formic acid removal.