Schaefer T, Herrmann H
Leibniz-Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstraße 15, Leipzig 04318, Germany.
Phys Chem Chem Phys. 2018 Apr 25;20(16):10939-10948. doi: 10.1039/c7cp08571k.
Oxygenated organic compounds are omnipresent in the troposphere, due to their strong emissions from either biogenic or anthropogenic sources. Additionally, the degradation and oxidation processes of volatile organic compounds (VOCs) result in the production of oxygenated organic compounds in the troposphere. The degradation and conversion of these compounds are often initiated by radical reactions and occur in the gas phase as well as in the aqueous phase, including cloud droplets, fog, haze, rain or hygroscopic particles containing 'aerosol liquid water (ALW)'. In the present study, the temperature-dependent OH radical reactions with oxygenated organic compounds in the aqueous phase have been investigated by laser flash photolysis. To determine the rate constants, the OH radical - thiocyanate anion competition kinetics method has been used. Once the organic reactant has an absorption at the excitation wavelength of the photolysis laser, the initial OH concentration decreases. This internal absorption effect leads to an overestimated rate constant of the investigated compound. The present study considers this contribution in order to clarify the internal absorption effect of the investigated organic compounds. The following rate constants for OH radical oxidation reactions of the oxygenated organic compounds have been obtained: acetone (2-propanone) k298K = (7.6 ± 1.0) × 107 L mol-1 s-1, 1-hydroxypropan-2-one k298K = (1.1 ± 0.1) × 109 L mol-1 s-1, 1,3-dihydroxypropan-2-one k298K = (1.5 ± 0.1) × 109 L mol-1 s-1, 2,3-dihydroxypropanal k298K = (1.3 ± 0.1) × 109 L mol-1 s-1, butane-1,3-diol k298K = (2.5 ± 0.1) × 109 L mol-1 s-1, butane-2,3-diol k298K = (2.0 ± 0.1) × 109 L mol-1 s-1 and hexane-1,2-diol k298K = (4.6 ± 0.4) × 109 L mol-1 s-1. With the rate constants obtained and their T-dependencies, the source and sink processes of oxygenated organic compounds in the tropospheric aqueous phase are arrived at precisely. These findings might enhance the predictive capabilities of models such as the chemical aqueous-phase radical mechanism (CAPRAM).
由于来自生物源或人为源的强烈排放，氧化有机化合物在对流层中无处不在。此外，挥发性有机化合物（VOCs）的降解和氧化过程导致对流层中产生氧化有机化合物。这些化合物的降解和转化通常由自由基反应引发，并且在气相以及水相中发生，包括云滴、雾、霾、雨或含有“气溶胶液态水（ALW）”的吸湿性颗粒。在本研究中，通过激光闪光光解研究了水相中OH自由基与氧化有机化合物的温度依赖性反应。为了确定速率常数，使用了OH自由基 - 硫氰酸根阴离子竞争动力学方法。一旦有机反应物在光解激光的激发波长处有吸收，初始OH浓度就会降低。这种内部吸收效应导致所研究化合物的速率常数被高估。本研究考虑了这一贡献，以阐明所研究有机化合物的内部吸收效应。已获得以下氧化有机化合物的OH自由基氧化反应的速率常数：丙酮（2 - 丙酮）k298K = (7.6 ± 1.0) × 107 L mol-1 s-1，1 - 羟基丙酮k298K = (1.1 ± 0.1) × 109 L mol-1 s-1，1,3 - 二羟基丙酮k298K = (1.5 ± 0.1) × 109 L mol-1 s-1，2,3 - 二羟基丙醛k298K = (1.3 ± 0.1) × 109 L mol-1 s-1，丁烷 - 1,3 - 二醇k298K = (2.5 ± 0.1) × 109 L mol-1 s-1，丁烷 - 2,3 - 二醇k298K = (2.0 ± 0.1) × 109 L mol-1 s-1和己烷 - 1,2 - 二醇k298K = (4.6 ± 0.4) × 109 L mol-1 s-1。利用获得的速率常数及其对温度的依赖性，可以精确得出对流层水相中氧化有机化合物的源和汇过程。这些发现可能会提高诸如化学水相自由基机制（CAPRAM）等模型的预测能力。
