Formation of Gas-Phase Hydrogen Peroxide via Multiphase Ozonolysis of Unsaturated Lipids
journal contributionposted on 11.12.2020, 18:08 by Zilin Zhou, Jonathan P. D. Abbatt
Gas-phase H2O2 is a prominent oxidant in the atmosphere. It also induces lung tissue damage and forest decline. Although it is known that ozonolysis of gas-phase alkenes leads to H2O2 formation at high relative humidities (RHs), little is known about this chemistry via gas-surface heterogeneous oxidation. Here, we quantitatively investigated the formation of H2O2 from surface ozonolysis of unsaturated lipids commonly found in human skin oil and atmospheric aerosol. This process is initiated by water reacting with Criegee intermediates (CIs), forming α-hydroxyhydroperoxides (α-HHPs) as the key intermediate products. α-HHPs are thermally stable molecules that act as reservoirs of H2O2 under dry conditions, prior to rapid decomposition to release H2O2 in the presence of water vapor. The upper limit of the α-HHP lifetime derived from oxidized methyl oleate was roughly 2 min at 50% RH. The molar H2O2 yields (relative to ozone consumption) vary from 7% to 35% for triolein, methyl oleate, and squalene, with no significant dependence on relative humidity from 50% to 80%. In contrast, oleic acid has the lowest H2O2 yield (∼2%), likely due to a more competitive reaction between CIs and its carboxylic acid headgroup. The implications of this chemistry in atmospheric and indoor environments are discussed.