Aqueous Phase Oligomerization of Methyl Vinyl Ketone by Atmospheric Radical Reactions

Abstract

Aqueous phase oxidation reactions in atmospheric particles can yield high molecular weight products and create secondary organic aerosol (SOA) upon droplet evaporation. Oxidation by hydroxyl radicals to create oligomers in solution that form SOA has been previously investigated; however, mixed organic solutions that can initiate radical chemistry have been largely overlooked. In aqueous solution, pyruvic acid (PA), an α-keto acid found in both the gas and aqueous phases in the atmosphere, photolyzes via a radical mechanism. Here, we use this photochemistry of pyruvic acid to trigger oligomerization of methyl vinyl ketone (MVK), an α,β-unsaturated compound generated by the atmospheric oxidation of isoprene. We closely compare the reaction products and mechanism to a recent work in which the radical oligomerization of MVK initiated by hydroxyl radical is studied in depth. Using mass spectrometry, it is shown that the two reactions create oligomers of similar molecular weights, up to m/z 1200 for initial MVK...