Atmospheric Fate of Lactones and Similar Cyclic Molecules

Science Center, Bent Corridor

Our research focused on measuring the oxidation products of lactone molecules and similar organic cyclic compounds under atmospheric conditions with the eventual hope of understanding the atmospheric oxidation of the compound hydroxymethylmethyl-α-lactone (HMML). This compound has been identified as a possible intermediate between isoprene, an extremely abundant biogenic volatile organic compound, and potentially harmful Secondary Organic Aerosols(SOAs). However, HMML’s instability means it could not be isolated for study leading us to investigate similar compounds that could indicate the relevant structure-reactivity relationships needed for an accurate prediction of HMML’s reactivity. We used Flow Tube Chemical Ionization Mass Spectrometry to measure the oxidation products with minimal fragmentation in the mass spectrum. In all, we studied four compounds under Chlorine atom- initiated oxidation conditions: Tetrahydrofuran, Cyclopentanone, -Propiolactone, and - Butyrolactone. Our experiments revealed a similar oxidation mechanism for all four compounds making it very probable that HMML follows a similar pattern of oxidation in the atmosphere. We also observed limited oxidation in all systems when hydroxyl radical was used to initiate oxidation. Since the hydroxyl radical is the dominant daytime oxidant in the atmosphere, this result suggests that the HMML reaction in the gas phase is relatively slow and that the reaction in the SOA phase may be more significant.