State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, China.
State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of China Meteorological Administration, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, China.
Sci Total Environ. 2020 Dec 20;749:142208. doi: 10.1016/j.scitotenv.2020.142208. Epub 2020 Sep 9.
NH, SO, NO and the inorganic ions of PM in winter 2009, 2014 and 2016 were examined to investigate the change in NH and aerosol chemistry in Beijing, China. NH concentrations showed an increase by 59% on average, in contrast to the decrease of SO by 63% from winter 2009 to 2016. The mean mass ratio of NH/NH was 0.83 ± 0.12 in 2016, which is higher than those obtained in 2009 and 2014, implying more NH remaining as free NH in 2016 winter. Our findings suggest that vehicles exhaust emissions are an important NH source in urban central atmosphere of Beijing in winter. Despite the observed NO presenting declining trends from 2014 to 2016, nitrate concentrations even exhibited a significant increasing trend, which may be largely attributable to high NH levels. An in-depth analysis of measured NH and aerosol species in a heavy pollution episode in December 2016, combined with the acidity predicted by ISORROPIA II model demonstrated abundant NH most of the time in air, where NH is not only a precursor for NH but also effect the neutralization of SO and NO in PM. With high RH and low photochemical activity, elevated NO concentration was attributed to an enhanced heterogeneous conversion of NO to HNO to form NHNO in pollution transport stage. The decrease in NO from high level and the increase in NH, with peaks of SO occurring were observed in pollution cumulative stage. The aqueous-phase oxidation of SO by NO to sulfate might play an important role with high pH values. Our results suggested that the simultaneous control of NH emissions in conjunction with SO and NO emissions would be more effective in reducing particulate matter PM formation.
NH、SO、NO 和 PM 中的无机离子在 2009 年、2014 年和 2016 年冬季进行了检测，以研究北京 NH 和大气气溶胶化学变化。NH 浓度平均增长了 59%，而 SO 浓度则从 2009 年到 2016 年下降了 63%。2016 年冬季 NH/NH 的平均质量比为 0.83±0.12，高于 2009 年和 2014 年，这表明 2016 年冬季有更多的 NH 以游离态 NH 的形式存在。我们的研究结果表明，在冬季北京城市中心大气中，车辆尾气排放是 NH 的重要来源。尽管观测到 2014 年至 2016 年期间 NO 呈下降趋势，但硝酸盐浓度甚至呈现出显著的上升趋势，这可能主要归因于高浓度的 NH。对 2016 年 12 月重度污染事件中测量的 NH 和大气气溶胶物种进行的深入分析，结合 ISORROPIA II 模型预测的酸度表明，空气中 NH 含量丰富，NH 不仅是 NH 的前体，而且影响 PM 中 SO 和 NO 的中和。由于 RH 高且光化学反应活性低，NO 浓度升高归因于在污染传输阶段，NO 向 HNO 的异相转化增强，形成 NHNO。在污染累积阶段，NO 浓度从高水平下降，NH 浓度升高，SO 浓度峰值出现。高 pH 值下，SO 通过 NO 的水相氧化生成硫酸盐可能会起到重要作用。我们的研究结果表明，同时控制 NH 排放以及 SO 和 NO 排放将更有效地减少颗粒物 PM 的形成。
