Environment Research Institute, Shandong University, Qingdao 266237, P. R. China.
College of Geography and Environment, Shandong Normal University, Jinan 250014, P. R. China.
Environ Sci Technol. 2021 Jun 15;55(12):7850-7857. doi: 10.1021/acs.est.1c01773. Epub 2021 May 21.
Nitrous acid (HONO) is a major source of hydroxyl (OH) radicals, and identifying its source is crucial to atmospheric chemistry. Here, a new formation route of HONO from the reaction of NO with Cl radicals with the aid of one or two water molecules [(Cl) (NO) (HO) ( = 1-2)] as well as on the droplet surface was found by Born-Oppenheimer molecular dynamic simulation and metadynamic simulation. The (Cl) (NO) (HO) (monohydrate) system exhibited a free-energy barrier of approximately 0.95 kcal mol, whereas the (Cl) (NO) (HO) (dihydrate) system was barrierless. For the dihydrate system and the reaction of NO with Cl radicals on the droplet surface, only one water molecule participated in the reaction and the other acted as the "solvent" molecule. The production rates of HONO suggested that the monohydrate system ([NO] = 8.56 × 10 molecule cm, [Cl] = 8.00 × 10 molecule cm, [HO] = 5.18 × 10 molecule cm) could account for 40.3% of the unknown HONO production rate () at site 1 and 53.8% of at site 2 in the East China Sea. This study identified the importance of the reaction system of NO, Cl, and water molecules in the formation of HONO in the marine boundary layer region.
亚硝酸（HONO）是羟基（OH）自由基的主要来源，确定其来源对于大气化学至关重要。本研究通过 Born-Oppenheimer 分子动力学模拟和元动力学模拟发现了一种新的 HONO 形成途径，即 NO 与 Cl 自由基在一个或两个水分子的辅助下[(Cl)(NO)(HO)(=1-2)]反应，以及在液滴表面上的反应。(Cl)(NO)(HO)(一水合物)体系的自由能势垒约为 0.95 kcal/mol，而(Cl)(NO)(HO)(二水合物)体系则没有势垒。对于二水合物体系和 NO 与 Cl 自由基在液滴表面上的反应，只有一个水分子参与反应，另一个水分子则作为“溶剂”分子。HONO 的生成速率表明，在东海站点 1 的[NO]=8.56×10 molecule cm、[Cl]=8.00×10 molecule cm、[HO]=5.18×10 molecule cm的一水合物体系可以解释未明 HONO 生成速率（）的 40.3%，站点 2 的则可以解释 53.8%。本研究确定了海洋边界层地区 NO、Cl 和水分子反应体系在 HONO 形成中的重要性。
