Reed Harris Allison E, Pajunoja Aki, Cazaunau Mathieu, Gratien Aline, Pangui Edouard, Monod Anne, Griffith Elizabeth C, Virtanen Annele, Doussin Jean-Francois, Vaida Veronica
Department of Chemistry and Biochemistry, CIRES, University of Colorado , Boulder, Colorado 80309, United States.
Department of Applied Physics, University of Eastern Finland , Kuopio Campus, P.O. Box 1627, 70211 Kuopio, Finland.
J Phys Chem A. 2017 May 11;121(18):3327-3339. doi: 10.1021/acs.jpca.7b01107. Epub 2017 Apr 17.
Aerosol and molecular processing in the atmosphere occurs in a complex and variable environment consisting of multiple phases and interfacial regions. To explore the effects of such conditions on the reactivity of chemical systems, we employ an environmental simulation chamber to investigate the multiphase photolysis of pyruvic acid, which photoreacts in the troposphere in aqueous particles and in the gas phase. Upon irradiation of nebulized pyruvic acid, acetic acid and carbon dioxide are rapidly generated, which is consistent with previous literature on the bulk phase photolysis reactions. Additionally, we identify a new C product, zymonic acid, a species that has not previously been reported from pyruvic acid photolysis under any conditions. Its observation here, and corresponding spectroscopic signatures, indicates it could be formed by heterogeneous reactions at the droplet surface. Prior studies of the aqueous photolysis of pyruvic acid have shown that high-molecular-weight compounds are formed via radical reactions; however, they are inhibited by the presence of oxygen, leading to doubt as to whether the chemistry would occur in the atmosphere. Identification of dimethyltartaric acid from the photolysis of multiphase pyruvic acid in air confirms radical polymerization chemistry can compete with oxygen reactions to some extent under aerobic conditions. Evidence of additional polymerization within the particles during irradiation is suggested by the increasing viscosity and organic content of the particles. The implications of multiphase specific processes are then discussed within the broader scope of atmospheric science.
大气中的气溶胶和分子过程发生在一个由多个相和界面区域组成的复杂多变的环境中。为了探究这些条件对化学系统反应性的影响，我们使用一个环境模拟舱来研究丙酮酸的多相光解，丙酮酸在对流层中于水性颗粒和气相中发生光反应。雾化的丙酮酸经辐照后，迅速生成乙酸和二氧化碳，这与之前关于体相光解反应的文献一致。此外，我们鉴定出一种新的C产物——酒酮酸，这是一种在任何条件下丙酮酸光解中此前均未被报道过的物质。在此处对它的观测以及相应的光谱特征表明，它可能是由液滴表面的非均相反应形成的。先前对丙酮酸水相光解的研究表明，高分子量化合物是通过自由基反应形成的；然而，它们会受到氧气存在的抑制，这让人怀疑这种化学反应在大气中是否会发生。在空气中多相丙酮酸光解中鉴定出二甲基酒石酸，证实了在有氧条件下自由基聚合化学在一定程度上可以与氧反应竞争。辐照期间颗粒内额外聚合的证据表现为颗粒粘度和有机含量的增加。然后在大气科学的更广泛范围内讨论了多相特定过程的影响。
