Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing100085, China.
Institute of Urban Meteorology, Chinese Meteorological Administration, Beijing100089, China.
Environ Sci Technol. 2023 Feb 21;57(7):2715-2725. doi: 10.1021/acs.est.3c00086. Epub 2023 Feb 1.
Particulate nitrate (NO) has currently become the major component of fine particles in the North China Plain (NCP) during winter haze episodes. However, the contributions of formation pathways to ground NO in the NCP are not fully understood. Herein, the NO formation pathways were comprehensively investigated based on model simulations combined with two-month field measurements at a rural site in the winter NCP. The results indicated that the nocturnal chemistry of NO hydrolysis aloft could contribute evidently to ground NO at the rural site during the pollution episodes with high aerosol water contents, achieving the contribution percentages of 25.2-30.4% of the total. In addition to the commonly proposed vertical mixing of breaking nocturnal boundary layer in the early morning, two additional transport pathways (frontal downdrafts and downslope mountain breezes) in the nighttime were found to make higher contributions to ground NO. Considering the dominant role (69.6-74.8%) of diurnal chemistry in NO formation, reduction of NO emissions in the daytime may be an effective control measure for reducing regional NO in the NCP.
颗粒态硝酸盐（NO）目前已成为华北平原冬季霾期间细颗粒物的主要成分。然而，对于该地区地面 NO 的形成途径仍不完全清楚。在此，基于模型模拟并结合冬季华北平原农村站点两个月的现场测量，对 NO 形成途径进行了综合研究。结果表明，在气溶胶含水量较高的污染期间，高空 NO 水解的夜间化学过程对农村站点的地面 NO 有显著贡献，达到总贡献的 25.2-30.4%。除了清晨打破夜间边界层的常见垂直混合外，夜间还发现了两种额外的输送途径（锋面下沉气流和下坡山风）对地面 NO 的贡献更高。考虑到白天化学过程对 NO 形成的主导作用（69.6-74.8%），减少白天的 NO 排放可能是减少华北地区区域 NO 的有效控制措施。
