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Published February 5, 2015 | Supplemental Material
Journal Article Open

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-R_n-COOH (R_n = C_2H_4, C_3H_6, C_4H_8, C_5H_10, and C_6H_12) microjets to ∼10 ns ·OH(g) pulses from the 266 nm laser photolysis of O3(g)/O_2(g)/H_2O(g) mixtures yields the corresponding (n–1) species O═C(H)-R_(n–1^-)COO–/HOOC-R_(n–1^-)COO^–, in addition to an array of closed-shell HOOC-R_n(-H)(OOH)-COO^–, HOOC-R_n(-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.

Additional Information

© 2015 American Chemical Society. Received: November 17, 2014; accepted: January 21, 2015; published: January 21, 2015. S.E. is grateful to Kurita Water and Environment Foundation and the Japan Science and Technology Agency (JST) PRESTO program. S.E. also thanks Prof. Hiroshi Masuhara for stimulating discussions. M.R.H. and A.J.C. acknowledge support from the National Science Foundation (U.S.A.) Grant AC-1238977.

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