Trace atmospheric concentrations of carboxylic acids have a potent effect upon the environment, where they modulate aqueous chemistry and perturb Earth’s radiative balance. Halogenated carboxylic acids are produced by the tropospheric oxidation of halocarbons and are considered persistent pollutants because of their weak tropospheric and aqueous sinks. However, recent studies reported rapid reactions between selected carboxylic acids and Criegee intermediates, which may provide an efficient gas-phase removal process. Accordingly, absolute rate coefficients of two Criegee intermediates, CH₂OO and (CH₃)₂COO, with a suite of carboxylic acids (HCOOH, CH₃COOH, CClF₂COOH, CF₃CF₂COOH, and pyruvic acid) were measured with a view to develop a structure–activity relationship (SAR). This SAR is based upon the dipole-capture model and predicts the reactivity of many further combinations of Criegee intermediates and carboxylic acids. Complementary synchrotron-based photoionization mass spectrometry measurements demonstrate that these reactions produce stable ester adducts, with a reaction coordinate involving transfer of the acidic hydrogen from the carboxylic acid to the terminal oxygen of the Criegee intermediate. The adduct products are predicted to have low vapor pressures, and coupling of this chemistry with a global atmospheric chemistry and transport model shows significant production of secondary organic aerosol at locations rich in biogenic alkene emissions.

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学员与羧酸的中间反应：大气中次级有机气溶胶的潜在来源

大气中痕量的羧酸对环境有强大的影响，在环境中它们会调节水化学反应并扰乱地球的辐射平衡。卤代羧酸是由卤代烃的对流层氧化产生的，由于其对流层和水槽较弱，因此被认为是持久性污染物。但是，最近的研究报道了选定的羧酸与Criegee中间体之间的快速反应，这可能提供有效的气相去除方法。因此，两种Criegee中间体CH ₂ OO和（CH ₃）₂ COO与一组羧酸（HCOOH，CH ₃ COOH，CClF ₂ COOH，CF ₃ CF为了建立结构-活性关系（SAR），对₂ COOH和丙酮酸进行了测量。该SAR基于偶极捕获模型，并预测了Criegee中间体和羧酸的许多其他组合的反应性。互补的基于同步加速器的光电离质谱测量表明，这些反应可生成稳定的酯加合物，其反应坐标涉及酸性氢从羧酸到Criegee中间体的末端氧的转移。预测该加合物产物的蒸气压低，并且这种化学方法与全球大气化学方法和运输模型的结合表明，在富含生物成因烯烃的地点大量生产了次级有机气溶胶。