Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada.
Department of Chemistry, University of Iowa, W285 Chemistry Building, Iowa City, Iowa 52242-1294, United States.
Environ Sci Technol. 2020 Oct 6;54(19):12484-12492. doi: 10.1021/acs.est.0c03331. Epub 2020 Sep 16.
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, 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.
光化学在大气水相中的发生既是有机化合物的源又是汇。在水相环境中，酸碱化学和扩展的水相 pH 值是在研究有机化合物动力学时需要考虑的一个重要但常常被忽视的因素。我们已经研究了作为 pH 函数的海松酸、海松醛、柠康酸和甲酸 (FA) 的水相 OH 氧化。我们还将研究扩展到了其他有机酸 (OAs)，这些 OAs 存在于α-蒎烯臭氧氧化产生的二次有机气溶胶 (SOA) 的水溶性部分。尽管所有的 OAs 在 pH 值为 10 时都表现出更高的 OH 反应性，但 FA（最小的 OA）和那些含有超过八个碳原子的 OA 之间的 pH 值依赖性有很大的不同。一个动力学箱模型也被用来描述我们的光反应器，并为我们的结果提供信心。我们的发现表明，大气中小 OAs（如 FA）的寿命对云水 pH 值非常敏感。然而，对于较大的 OAs 和许多其他α-蒎烯 SOA 中的 OAs，其影响要小得多。这些结果对于简化云水化学模型非常重要。
