Criegee Chemistry on Aqueous Organic Surfaces

In the troposphere, the fate of gas-phase Criegee intermediates (CIs) is deemed to be determined by their reactions with water molecules. Here it is shown that CIs produced in situ on the surface of water/acetonitrile (W/AN) solutions react competitively with millimolar carboxylic acids. Present experiments probe, via online electrospray mass spectrometry, CIs' chemistry on the surface of α-humulene and β-caryophyllene in W/AN microjets exposed to O₃(g) for <10 μs. Mass-specific identification lets us establish the progeny of products and intermediates generated in the early stages of CIs' reactions with H₂O, D₂O, H₂¹⁸O, and n-alkyl-COOH (n = 1-7). It is found that n-alkyl-COOH competes for CIs with interfacial water, their competitiveness being an increasing function of n. Present findings demonstrate that CIs can react with species other than H₂O on the surface of aqueous organic aerosols due to the low water concentrations prevalent in the outermost interfacial layers.