Temperature- and pH- Dependent OH Radical Reaction Kinetics of Tartaric and Mucic Acids in the Aqueous Phase

Abstract

Tartaric acid and mucic acid are dicarboxylic acids (DCAs), a substance class often found in atmospheric aerosols and cloud droplets. The hydroxyl radical ( • OH)-induced oxidation in the aqueous phase is known to be an important loss process of organic compounds such as DCAs. However, the study of • OH kinetics of DCAs in the aqueous phase is still incomplete. In the present study, the rate constants of the • OH reactions of tartaric acid and mucic acid in the aqueous phase were determined by the thiocyanate competition kinetics method as a function of temperature and pH. The following T-dependent Arrhenius expressions (in units of L mol −1 s −1 ) were first derived for the • OH reactions with tartaric acid�k(T, H 2 A) = (3.3 ± 0.1) × 10 10 exp[(−1350 ± 110 K)/T], k(T, HA − ) = (3.6 ± 0.1) × 10 10 exp[(−580 ± 110 K)/T], and k(T, A 2− ) = (3.3 ± 0.1) × 10 10 exp[(−1190 ± 170 K)/T]�as well as mucic acid�k(T, H 2 A) = (2.2 ± 0.1) × 10 10 exp[(−1140 ± 150 K)/T], k(T, HA − ) = (4.8 ± 0.1) × 10 10 exp[(−1280 ± 170 K)/T], and k(T, A 2− ) = (2.1 ± 0.1) × 10 10 exp[(−970 ± 70 K)/T]. A general trend of the • OH rate constant is found asThe pH-and temperaturedependent rate constants of the OH radical reactions allow an accurate description of the source and sink processes in the tropospheric aqueous phase.

Deactivating Effect of Hydroxyl Radicals Reactivity by Sulfate and Sulfite Functional Groups in Aqueous Phase─Atmospheric Implications for Small Organosulfur Compounds

“…Alternatively, it should be noted that SAR methods are developed based on measurement rate constants and primarily consider • OH reactions with organic compounds via H-abstraction . However, OH radicals may initiate reactions through alternative pathways such as electron-transfer and • OH-addition. , For instance, • OH oxidation of carboxylic acids can proceed through an electron transfer pathway, involving the interaction between the carboxylate group (−COO – ) and • OH radicals, and resulting in the fragmentation of organic compounds with the elimination of CO 2 . ,, Although these processes are typically considered to be insignificant for alkyl organics, further investigations are warranted to more comprehensively assess the significance of these processes in • OH reactions with organosulfur compounds in aqueous phase.…”

“…We used a laser photolysis-long path absorption (LP–LPA) setup to determine the second-order rate constants of • OH with organosulfur compounds in aqueous phase (Figure S1 of the Supporting Information, SI). A detailed description of this setup has been previously provided. − Briefly, this setup consisted of an excimer laser (Model COMPex 200, Lambda-Physik) that emitted a pulse at a wavelength of λ = 248 nm, with a duration of 20 ns and a frequency of 4 Hz. A continuous-wave ( cw ) laser (Model Radius 405, Coherent) generated the analytical laser beam with a wavelength of λ = 407 nm.…”

“…tion of organic compounds with the elimination of CO 2 . 47,48,52 Although these processes are typically considered to be insignificant for alkyl organics, 91 further investigations are warranted to more comprehensively assess the significance of these processes in • OH reactions with organosulfur compounds in aqueous phase.…”

Aqueous Radical Initiated Oxidation of an Organic Monolayer at the Air–Water Interface as a Proxy for Thin Films on Atmospheric Aerosol Studied with Neutron Reflectometry

“…refs ,,− ,− . Few studies have focused on oxidation of thin films from the aqueous phase; however, an increasing number of recent studies focus on aqueous phase oxidation in the bulk ,,− ,, and in particular by the aqueous phase OH radical. − ,,,− Other relevant studies include that of Sarang et al, who considered aqueous phase oxidation of so-called “Green Leaf Volatiles”, unsaturated oxygenated hydrocarbons (volatile species emitted from plants that can partition into water), by • OH, SO 4 •– , and NO 3 • , and that of Tran et al, who studied oxidation by the aqueous phase SO 4 •– of a number of organic aerosol compounds including isoprene related compounds, lactic and pyruvic acid.…”

“…There have been several studies on the oxidation of thin films by gaseous phase oxidants, e.g. refs 25,35,53−55,91−94. Few studies have focused on oxidation of thin films from the aqueous phase; 44 however, an increasing number of recent studies focus on aqueous phase oxidation in the bulk 88,89,[95][96][97][98][99][100]90,101 and in particular by the aqueous phase OH radical. 88−90,95,96,99−101 Other relevant studies include that of Sarang et al, 97 who considered aqueous phase oxidation of so-called "Green Leaf Volatiles", unsaturated oxygenated hydrocarbons (volatile species emitted from plants that can partition into water), by • OH, SO 4…”