Apparent Tropospheric Observation of Criegee Intermediate Oligomerization Reaction Signatures

Criegee intermediates are zwitterionic carbonyl oxide reactive intermediates that are implicated in transforming the composition of Earth’s troposphere and in the formation of secondary organic aerosol, impacting Earth’s radiation balance, air quality and human health. Yet, direct identification of their signatures in the field remains elusive. From particulate and gas-phase mass spectrometric measurements in the Amazon rainforest, we identify sequences of masses that are consistent with expected signatures of oligomerization of the CH2OO Criegee intermediate, a process implicated in ozonolysis-driven aerosol formation. We assess the potential contributions of oligomerization through laboratory ozonolysis experiments, direct kinetic studies of Criegee intermediate reactions, and high-level theoretical calculations. Global atmospheric models built on these kinetics results indicate that Criegee intermediate chemistry may play a larger role in altering the composition of Earth’s troposphere than is captured in current atmospheric models, especially in areas of high humidity. However, the models still capture only a relatively small fraction of the observed signatures, suggesting the considerable underestimates of Criegee intermediate concentrations and reactivity and/or the dominance of other oxidation mechanisms. Resolving remaining uncertainties in emission inventories and the effects of atmospheric water vapor on key chemical reactions will be required to definitively assess the role of Criegee intermediate oligomerization reactions.