Abstract：
To explore the content and variation characteristics of water-soluble ions of atmospheric fine particles (PM2.5) in a Beijing urban area and put forward the pollution prevention and control scheme, the water-soluble ions, gaseous precursors (SO2, NO2), and meteorological factors (temperature, RH) of PM2.5 in 2022 were analyzed and determined. The results showed that the water-soluble ions with the highest proportion in PM2.5 in the Beijing City urban area were NO3-, NH4+, and SO42-, accounting for 52.7% of PM2.5. The mass concentrations of PM2.5 and SNA were lower than the historical results, whereas the proportion of SNA, SOR, and NOR was higher than the historical results. This showed that the fine particulate matter pollution in Beijing has been significantly improved, but it still has strong secondary pollution characteristics. NO3-/SO42-(2.2) was higher than those of historical and nearby provinces and cities, reflecting the expanding influence of mobile sources. In terms of seasonal variation, PM2.5 showed the characteristic of high in autumn and low in summer. The proportion of NO3- was the highest in autumn, spring, and winter; the proportion of SO42- was the highest in summer; and the proportion of NH4+ changed little in each season. The seasonal variation rules of NOR and SOR were almost opposite, which reflected the difference in transformation factors between NOR and SOR. The main forms of SNA in the Beijing urban area were NH4NO3 and (NH4)2SO4. The neutralization degree of cations and anions was the highest in winter, the cation NH4+ was slightly insufficient in summer, and NH4+ was in excess in spring and autumn. The Beijing urban area was an ammonia-rich environment. In terms of pollution level, RH, particulate matter moisture, and water-soluble ions mass concentration all increased with the increase in pollution level, and SNA increased fastest, with its proportion in PM2.5 increasing first and then stabilizing, whereas the contribution rate of other water-soluble ions decreased gradually. In terms of spatial distribution, the mass concentration relationship of SNA at the central urban area and suburbs was NO3- > SO42- > NH4+, which reflected the pollution characteristics dominated by NO3-. The highest contribution rate of SNA to PM2.5 occurred in the eastern region, the central urban area, and the transmission point, indicating that the secondary reaction was relatively active in the central urban area and the eastern region, and the regional transport was also an important source of secondary ions.
摘要：
探讨北京某城区大气细颗粒物(PM2.5)中水溶性离子的含量及变化特征,提出污染防治方案。水溶性离子，气态前体（SO2，NO2），和气象因素(温度，对2022年PM2.5的RH）进行了分析测定。结果表明,北京市城区PM2.5中水溶性离子含量最高的是NO3-,NH4+,和SO42-，占PM2.5的52.7%。PM2.5和SNA的质量浓度低于历史结果，而SNA的比例，SOR,NOR高于历史结果。这表明北京市细颗粒物污染状况有了明显改善,但仍具有较强的二次污染特征。NO3-/SO42-(2.2)高于历史及附近省市,反映了移动源不断扩大的影响力。从季节变化来看,PM2.5呈现秋高夏低的特征。秋季NO3-的比例最高，spring,和冬季；夏季SO42-的比例最高；NH4的比例在每个季节变化不大。NOR和SOR的季节变化规律几乎相反，这反映了NOR和SOR之间转换因子的差异。北京市区SNA的主要形态为NH4NO3和(NH4)2SO4。冬季阳离子和阴离子的中和度最高，夏季，阳离子NH4+略有不足，春季和秋季NH4过量。北京城区是一个富含氨的环境。就污染程度而言,RH,颗粒物水分，和水溶性离子质量浓度都随着污染水平的增加而增加，SNA增长最快，其在PM2.5中的比例先增加后稳定，其他水溶性离子的贡献率逐渐降低。在空间分布方面,SNA在中心城区和郊区的质量浓度关系为NO3->SO42->NH4+,反映了以NO3-为主的污染特征。SNA对PM2.5的贡献率最高的是东部地区,中心城区,和传输点，表明中心城区和东部地区的二级反应相对活跃，区域运输也是二次离子的重要来源。
