北京市2018年春季一次沙尘回流过程的污染特征

通过监测数据分析，结合轨迹模拟和特征雷达图的分析结果，对2018年4月14~19日北京出现的一次沙尘天气过程进行分析.结果显示：依据ρ（PM_2.5）和ρ（PM₁₀）及其比值PM_2.5/PM₁₀ρ（PM_2.5）/ρ（PM₁₀），下同]的变化情况，此次沙尘过程可分为沙尘期、中间期、回流期和回流后期4个典型时期.沙尘期ρ（PM₁₀）平均值达到（278.5±83.7）μg/m³，明显高于回流期和回流后期，回流后期ρ（PM_2.5）平均值达到（135.5±16.9）μg/m³，明显高于回流期和沙尘期.沙尘期逐小时PM_2.5/PM₁₀<0.2，回流期和回流后期PM_2.5/PM₁₀比值分别介于0.3~0.6和0.5~0.8范围内.SO₄^2-、NO₃^-和NH₄⁺等（SNA）水溶性离子沙尘期浓度占比仅为7.3%±2.5%，沙尘回流期和回流后期SNA占比分别增长至47.0%±6.3%和51.3%±5.7%.研究表明，受天气系统影响，回流沙尘可裹挟南部的细颗粒和气态污染物输送到北京后发生累积和二次转化，从而推高PM_2.5浓度，因此发生沙尘回流时，区域内应加强一次污染物排放的管控力度，同时北京市需进一步加强机动车氮氧化物的排放监管.

Pollution characteristics of a dust backflow process in Beijing in the spring of 2018

The characteristics of a dust backflow air pollution process in Beijing from Apr. 14^th to 19^th, 2018 were analyzed based on air quality monitoring data, air parcel back trajectory and air pollution characteristic radar chart. According to ρ(PM_2.5), ρ(PM₁₀) and the mass concentration ratio of PM_2.5 to PM₁₀ (PM_2.5/PM₁₀), the entire episode can be divided into four stages:dust stage, intermediate stage, dust backflow stage and post-backflow stage. The highest stage-mean mass concentration of PM₁₀ was observed in the dust stage at (278.5±83.7) μg/m³, and the highest stage-mean mass concentration of PM_2.5 was observed in the post-backflow stage at (135.5±16.9) μg/m³. In addition, the PM_2.5/PM₁₀ was less than 0.2 in the dust stage, and increased to 0.3~0.6 in the dust backflow stage and 0.5~0.8 in the post-backflow stage. The mass fraction of water-soluble inorganic ions (SO₄^2-, NO₃^- and NH₄⁺ in total) in PM_2.5 was 7.3%±2.5% in dust stage, whereas it increased to 47.0%±6.3% in the dust backflow stage and 51.3%±5.7% in the post-backflow stage. This work revealed that particulate and gaseous pollutants from the south part in Beijing-Tianjin-Hebei region were transported to Beijing together with backflow dust, which in part accounted for the PM_2.5 increase in Beijing. Therefore, regional air pollutant emission should be strengthened in dust weather process when dust backflow occurs. Meanwhile, Beijing should reinforce the regulation of vehicle emissions.