Xia Sha-Sha, Eugene Alexis J, Guzman Marcelo I
Department of Chemistry , University of Kentucky , Lexington , Kentucky 40506 , United States.
J Phys Chem A. 2018 Aug 9;122(31):6457-6466. doi: 10.1021/acs.jpca.8b05724. Epub 2018 Jul 25.
Aerosols of variable composition, size, and shape are associated with public health concerns as well as with light-particle interactions that play a role in the energy balance of the atmosphere. Photochemical reactions of 2-oxocarboxylic acids in the aqueous phase are now known to contribute to the total secondary organic aerosol (SOA) budget. This work explores the cross reaction of glyoxylic acid (GA) and pyruvic acid (PA) in water, the two most abundant 2-oxocarboxylic acids in the atmosphere, under solar irradiation and dark thermal aging steps. During irradiation, PA and GA are excited and initiate proton-coupled electron transfer or hydrogen abstraction and α-cleavage reactions, respectively. The time series of photoproducts is studied by ion chromatography (IC) with conductivity and electrospray ionization (ESI) mass spectrometry (MS) detection, direct ESI-MS analysis in the negative ion mode, and nuclear magnetic resonance spectroscopy (NMR). The use of one-dimensional (H and C NMR) and two-dimensional NMR techniques includes gradient correlation spectroscopy (gCOSY) and heteronuclear single quantum correlation (HSQC). The aging of photoproducts in the dark is monitored by UV-visible spectroscopy. The periodicity in the time domain of the optical properties is explained in terms of chromophores that undergo alternating thermochromism and photobleaching between nighttime and daytime cycles, respectively. A reaction mechanism for the cross reaction of GA and PA explaining the generation of trimers with general formulas CHO (148 Da), CHO (162 Da), and CHO (164 Da) is provided based on all experimental observations.
成分、大小和形状各异的气溶胶与公众健康问题以及在大气能量平衡中起作用的轻粒子相互作用相关。现在已知水相中2-氧代羧酸的光化学反应对二次有机气溶胶（SOA）总量有贡献。这项工作研究了大气中最丰富的两种2-氧代羧酸——乙醛酸（GA）和丙酮酸（PA）在水中，在太阳辐射和黑暗热老化步骤下的交叉反应。在辐射过程中，PA和GA分别被激发并引发质子耦合电子转移或氢原子提取以及α-裂解反应。通过离子色谱（IC）结合电导和电喷雾电离（ESI）质谱（MS）检测、负离子模式下的直接ESI-MS分析以及核磁共振光谱（NMR）研究光产物的时间序列。使用一维（H和C NMR）和二维NMR技术，包括梯度相关光谱（gCOSY）和异核单量子相关（HSQC）。通过紫外可见光谱监测光产物在黑暗中的老化。光学性质在时域中的周期性是根据分别在夜间和白天循环中经历交替热致变色和光漂白的发色团来解释的。基于所有实验观察结果，提供了一个GA和PA交叉反应的反应机制，解释了通式为CHO（148 Da）、CHO（162 Da）和CHO（164 Da）的三聚体的生成。
