Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), CNRS-Université Orléans-CNES, 45071 Orléans Cedex 2, France.
Environ Sci Technol. 2020 Sep 15;54(18):11048-11057. doi: 10.1021/acs.est.0c01832. Epub 2020 Sep 1.
Nitrous acid (HONO) is a major precursor of tropospheric hydroxyl radical (OH) that accelerates the formation of secondary pollutants. The HONO sources, however, are not well understood, especially in polluted areas. Based on a comprehensive winter field campaign conducted at a rural site of the North China Plain, a box model (MCM v3.3.1) was used to simulate the daytime HONO budget and nitrate formation. We found that HONO photolysis acted as the dominant source for primary OH with a contribution of more than 92%. The observed daytime HONO could be well explained by the known sources in the model. The heterogeneous conversion of NO on ground surfaces and the homogeneous reaction of NO with OH were the dominant HONO sources with contributions of more than 36 and 34% to daytime HONO, respectively. The contribution from the photolysis of particle nitrate and the reactions of NO on aerosol surfaces was found to be negligible in clean periods (2%) and slightly higher during polluted periods (8%). The relatively high OH levels due to fast HONO photolysis at the rural site remarkably accelerated gas-phase reactions, resulting in the fast formation of nitrate as well as other secondary pollutants in the daytime.
亚硝酸（HONO）是大气羟基自由基（OH）的主要前体，可加速二次污染物的形成。然而，HONO 的来源，特别是在污染地区，还没有得到很好的理解。基于在中国华北平原农村地区进行的一次综合冬季野外考察，使用箱式模型（MCM v3.3.1）模拟了白天 HONO 的收支和硝酸盐的形成。我们发现，HONO 光解作用是主要的 OH 来源，其贡献超过 92%。观测到的白天 HONO 可以通过模型中已知的来源很好地解释。地面表面上的 NO 的非均相转化和 NO 与 OH 的均相反应是 HONO 的主要来源，分别占白天 HONO 的 36%和 34%以上。在清洁期（2%），发现来自颗粒硝酸盐光解和气溶胶表面上的 NO 反应的贡献可以忽略不计，而在污染期，其贡献略高（8%）。由于农村地区亚硝酸快速光解导致的相对较高的 OH 水平，显著加速了气相反应，导致硝酸盐以及其他二次污染物在白天快速形成。
