Photochemical processing taking place in atmospheric aqueous phases serves as both a source and a sink of organic compounds. In aqueous environments, acid–base chemistry and, by extension, aqueous-phase pH, are an important yet often neglected factors to consider when investigating the kinetics of organic compounds. We have investigated the aqueous-phase OH-oxidation of pinic acid, cis-pinonic acid, limononic acid, and formic acid (FA) as a function of pH. We have also extended our studies to other organic acids (OAs) present in the water-soluble fraction of secondary organic aerosol (SOA) arising from the ozonolysis of α-pinene. Although all the OAs exhibited larger OH reactivities at pH 10, the pH dependence was dramatically different between FA, the smallest OA, and those that contained more than eight carbons. A kinetic box model was also employed to characterize our photoreactor and to provide confidence to our results. Our finding shows that the atmospheric lifetimes of small OAs (e.g., FA) are highly sensitive to cloud water pH. However, those of larger OAs and many other OAs in α-pinene SOA are affected to a much less extent. These results are of great importance for the simplification of cloud water chemistry models.

中文翻译：

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pH值取决于有机酸在水相中的OH反应性。

在大气水相中进行的光化学处理既是有机化合物的来源，又是有机化合物的来源。在水性环境中，研究有机化合物动力学时要考虑的重要因素是酸碱化学以及扩展的水相pH。我们研究了松酸顺式的水相OH-氧化品酸，柠檬酸和甲酸（FA）与pH的关系。我们还将研究范围扩展到α-pine烯的臭氧分解产生的次要有机气溶胶（SOA）的水溶性部分中存在的其他有机酸（OAs）。尽管所有OA在pH 10时都表现出更大的OH反应性，但FA，最小的OA和碳原子数超过8的FA之间的pH依赖性显着不同。还使用了动力学盒模型来表征我们的光反应器并为我们的结果提供信心。我们的发现表明，小OA（例如FA）的大气寿命对云水pH值高度敏感。但是，α-pine烯SOA中较大的OA和许多其他OA受到的影响要小得多。这些结果对于简化云水化学模型具有重要意义。