Enhanced nitrous acid(HONO)formation via NO_(2)uptake and its potential contribution to heavy haze formation during wintertime

full understanding of the sources of atmospheric nitrous acid(HONO)in the polluted urban atmosphere re-mains a challenge.In this study,ambient HONO and relevant species were measured during January 2019 at an urban site in Beijing,China,and a budget analysis of HONO was conducted using a box model combined with field observations.Large nighttime“missing sources”of HONO were identified on heavily polluted days based on traditional sources,which had a significant correlation with the relative humidity,ammonia(NH_(3)),and aerosol surface area,and the promotional effect of NH_(3)for nitrogen dioxide(NO_(2))uptake on the wet aerosol surface was discussed.Then,an updated parameterization scheme for quantifying the enhanced heterogeneous reactions of NO_(2)on aerosol surfaces is proposed,and the missing nighttime sources of HONO could be substantially com-pensated after the new scheme was incorporated.Further evaluation on the contributions of HONO to hydroxyl radicals was conducted,and the authors found that the photolysis of HONO played a dominant role in the primary OH production on the polluted days(78%-90%).The study reveals great potential of an NH3-enhanced uptake coefficient of NO_(2)on the aerosol surface in the nocturnal HONO budget,and highlights the significance of HONO in the strong atmospheric oxidation capability during episodes with a heavily polluted atmosphere.

本文研究了重污染过程中气态亚硝酸(HONO)的关键来源并基于化学箱模型对其源汇过程进行了闭合分析.结果显示,现有的HONO源汇机制并不能解释观测期间出现的高HONO事件,尤其是重污染过程夜间存在大量的HONO"未知源".本文提出了一套新的HONO源汇参数化方案,可以较好的模拟观测期间HONO日间和夜间来源,并进一步评估了HONO对羟基自由基(OH)的贡献,发现HONO光解主导了重污染天OH生成(78%–90%).研究结果揭示了华北城市富氨大气环境促进NO_(2)在气溶胶表面的摄取和非均相反应进而主导了夜间HONO生成,凸显了HONO化学对于重污染过程维持大气氧化能力的重要作用.