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 NO₂ 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 NO₂ 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.

中文翻译：

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华北平原地区的HONO预算及其在硝酸盐形成中的作用。

亚硝酸（HONO）是对流层羟基自由基（OH）的主要前体，可加速二次污染物的形成。然而，人们对HONO的来源知之甚少，尤其是在污染地区。基于在华北平原农村地区进行的一次全面的冬季野外运动，使用箱型模型（MCM v3.3.1）模拟白天的HONO预算和硝酸盐形成。我们发现HONO光解是伯OH的主要来源，贡献超过92％。模型中的已知来源可以很好地解释观测到的白天HONO。NO ₂的异质转化NO在地面上的分布以及NO与OH的均匀反应是主要的HONO来源，分别对白天HONO的贡献超过36％和34％。发现硝酸盐粒子的光解作用和NO ₂在气溶胶表面反应的贡献在清洁时期（2％）可忽略不计，而在污染时期（8％）则略高。由于农村地区HONO的快速光解而导致的相对较高的OH含量显着加快了气相反应，导致白天硝酸盐及其他次级污染物的快速形成。