Rapid Aqueous-Phase Hydrolysis of Ester Hydroperoxides Arising from Criegee Intermediates and Organic Acids

Stabilized Criegee intermediates react with organic acids in the gas phase and at the air water interface to form a class of ester hydroperoxides, alpha-acyloxyalkyl hydroperoxides (alpha AAHPs). A number of recent studies have proposed the importance of alpha AAHPs to the formation and growth of secondary organic aerosol (SOA). The chemistry of alpha AAHPs has not been investigated due to a lack of commercially available chemical standards. In this work, the behavior of alpha AAHPs in condensed phases is investigated for the first time. Experiments were performed with two synthesized aAAHP species. alpha AAHPs decomposed rapidly in the aqueous phase, with the rate highly dependent on the solvent, temperature, solution pH, and other compounds present in the solution. The measured 1st-order decomposition conditions examined in this work. Elucidation of the reaction mechanism is complicated by byproducts arising from the synthetic procedure, but observations are consistent with a base-catalyzed hydrolysis of alpha AAHPs. The rapid hydrolysis of alpha AAHPs observed in this work implies their short lifetimes in ambient cloud and fog waters. Decomposition of alpha AAHPs likely gives rise to smaller peroxides, such as H2O2. The loss of alpha AAHPs is also relevant to filter extraction, which is commonly practiced in laboratory experiments, potentially explaining contradictory results reported in the existing literature regarding the importance of alpha AAHPs in SOA.