Prompt Formation of Organic Acids in Pulse Ozonation of Terpenes on Aqueous Surfaces

A major atmospheric process, the gas-phase ozonation of terpenes yields suites of products via a cascade of chemically activated intermediates that ranges from primary ozonides to dioxiranes. If a similar mechanism operated in water, as it is generally assumed, such intermediates would be deactivated within picoseconds and, henceforth, be unable to produce carboxylic acids in microseconds. Herein, we report the online electrospray mass spectrometric detection of (M + 2O − H + ) and (M + 3O − H + ) carboxylates on the surface of aqueous β-caryophyllene (C 15 H 24, M = 204 Da) microjets exposed to a few ppmv of O 3 (g) for <10 μs. Since neither species is formed on dry solvent microjets and both incorporate deuterium from D 2 O, we infer that carboxylates ensue from the interaction of nascent intermediates with interfacial water via heretofore unreported processes. These interfacial events proceed much faster than those in bulk liquids saturated with ozone.