Key Laboratory of Resources and Environmental Systems Optimization, Ministry of Education, College of Environmental Science and Engineering, North China Electric Power University, Beijing, 102206, China.
Key Laboratory of Resources and Environmental Systems Optimization, Ministry of Education, College of Environmental Science and Engineering, North China Electric Power University, Beijing, 102206, China.
Environ Pollut. 2021 Dec 15;291:118151. doi: 10.1016/j.envpol.2021.118151. Epub 2021 Sep 9.
Ammonia is essential for the generation of secondary inorganic aerosols (SIA) in particulate matter, which affects severely the air quality in north China. In this study, PM sampling was conducted as well as gaseous pollutant concentration and meteorological parameters were measured from November 2017 to January 2018. PM concentration was highest in the industrial site (94.8 ± 41.7 μg m), followed by urban (40.9 ± 24.1 μg m) and rural (35.6 ± 20.3 μg m) sites. The mass ratio of NO/SO exhibited clear site variations, with the highest average value of 1.2 was found at the urban site, likely due to the dense traffic volume resulting in higher emissions of NO, and the lowest value of 0.9 at the industry site. The presence of Excess-NHx (E-NHx), raising the pH 24 by 1.4, 1.3, and 1.4 units in industry, urban, and rural sites, respectively, might be vital for raising the aerosol pH. Correlation coefficients of Nitrogen oxidation rate (NOR, NOR = [NO]/[NO] + [NO]) vs. Photochemical oxidants (O, NO +O in our study) and NOR vs. aerosol water content (AWC) at three sites were implied that both homogeneous and heterogeneous reactions occurred for nitrate formation in industry site, while heterogeneous reactions were dominant in urban and rural sites. Oxidation rates were most sensitive to the variation of E-NHx concentration at rural site, followed by the urban and industry sites, which was shown by the fact that the increase in E-NHx concentration by 1.0 μg m increased the SIA concentration by 1.21, 1.02, and 0.37 μg m at rural, urban, and industry sites, respectively. With the increase in NH emissions at present, the role of NH in SIA formation at ammonia-rich atmosphere requires more attention, especially in the less-noticed rural areas.
氨是颗粒物中次生无机气溶胶（SIA）形成的必要物质，这严重影响了中国北方的空气质量。在这项研究中，我们从 2017 年 11 月到 2018 年 1 月进行了 PM 采样，并测量了气态污染物浓度和气象参数。PM 浓度在工业区最高（94.8±41.7μg/m³），其次是市区（40.9±24.1μg/m³）和农村（35.6±20.3μg/m³）。NO/SO 的质量比表现出明显的站点差异，市区的平均比值最高，为 1.2，这可能是由于交通流量密集导致 NO 排放量较高，而工业区的比值最低，为 0.9。存在过剩的 NHx（E-NHx），使工业区、市区和农村的 pH 分别升高了 1.4、1.3 和 1.4 个单位，这对于提高气溶胶 pH 值可能是至关重要的。三个站点的氮氧化速率（NOR，NOR=[NO]/[NO]+[NO]）与光化学氧化剂（O，在我们的研究中为 NO+O）以及 NOR 与气溶胶含水量（AWC）的相关系数表明，硝酸盐的形成既发生了均相反应，也发生了非均相反应，而在市区和农村站点，非均相反应占主导地位。在农村站点，氧化速率对 E-NHx 浓度的变化最敏感，其次是市区和工业区，这表明 E-NHx 浓度增加 1.0μg/m³会使 SIA 浓度分别增加 1.21、1.02 和 0.37μg/m³。随着目前 NH 排放的增加，NH 在富氨大气中 SIA 形成中的作用需要更多的关注，特别是在不太受关注的农村地区。
