Stepwise Oxidation of Aqueous Dicarboxylic Acids by Gas-Phase OH Radicals.
A leading source of uncertainty in predicting the climate and health effects of secondary organic aerosol (SOA) is how its composition changes over their atmospheric lifetimes. Because dicarboxylic acid (DCA) homologues are widespread in SOA, their distribution provides an ideal probe of both aerosol age and the oxidative power of the atmosphere along its trajectory. Here we report, for the first time, on the oxidation of DCA(aq) by ·OH(g) at the air-water interface. We found that exposure of aqueous HOOC-Rn-COOH (Rn = C2H4, C3H6, C4H8, C5H10, and C6H12) microjets to ∼10 ns ·OH(g) pulses from the 266 nm laser photolysis of O3(g)/O2(g)/H2O(g) mixtures yields the corresponding (n-1) species O═C(H)-Rn-1-COO(-)/HOOC-Rn-1-COO(-), in addition to an array of closed-shell HOOC-Rn(-H)(OOH)-COO(-), HOOC-Rn(-2H)(═O)-COO(-), HOOC-Rn(-H)(OH)-COO(-), and radical HOOC-Rn(-H)(OO·)-COO(-) species. Oxalic and malonic acids, which are shown to be significantly less hydrophobic and reactive than their higher homologues, will predictably accumulate in SOA, in accordance with field observations.
†The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8302, Japan.|‡Research Institute for Sustainable Humanosphere, Kyoto University, Uji 611-0011, Japan.|§PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
Shinichi
S
Enami
∥Linde Center for Global Environmental Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States.
Michael R
MR
Hoffmann
∥Linde Center for Global Environmental Science, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, United States.
Agustín J
AJ
Colussi
HOx chemistry; amphiphiles; photochemical aging; surface chemistry; surfactant; troposphere