利用NCEP再分析资料、逐小时污染物浓度数据、风廓线雷达及地面常规观测资料，对北京2018年3月26—29日一次“先霾后沙”的空气污染过程进行了分析。结果表明：霾污染期间PM2.5峰值浓度为242 μg·m-3，PM2.5/PM10值为0.86。受蒙古气旋影响，PM10浓度出现爆发性增长，增长速率达到912 μg·m-3·h-1，PM2.5/PM10值下降至0.11。霾主要影响时段边界层内以西南风为主，平均通风量为15 907 m2·s-1，大气边界层以稳定的弱上升或下沉运动为主；而沙尘影响时段平均通风量为9 226 m2·s-1，沙尘天气爆发前边界层明显的下沉运动先于地面污染物浓度的变化。基于后向轨迹模式和潜在源贡献分析方法PSCF计算结果，霾影响时段河北中南部、山西中部等地对北京PM2.5贡献较多；而沙尘影响时段，北京地区的PM10主要来源于内蒙古中部和辽宁西部。
In this paper, the global NCEP reanalysis data, hourly pollutant concentration data, wind profiler radar and ground routine observation data in Beijing were used to analyze a haze-dust pollution process from March 26 to March 29, 2018. The results showed that the PM2.5 peak concentration was 242 μg·m-3, and PM2.5/PM10 ratio was 0.86 during haze period. Affected by Mongolian cyclone, the concentration of PM10 increased explosively, and the growth rate reached 912 μg·m-3·h-1, and the proportion of PM2.5/PM10 decreased to 0.11. By analyzing of the horizontal wind field, ventilation index and vertical velocity in the boundary layer, it could be seen that the southwest wind dominated the boundary layer during haze period, and the average ventilation index was 15 907 m2·s-1. The steady weak upward or subsidence movement was dominant. In the period of sand, the average ventilation index was 9 226 m2·s-1. Vertical velocity was earlier than variation of pollutant concentration in advance. Based on the backward trajectory model and potential source contribution analysis method (PSCF) results, central and southern Hebei province and central Shanxi province contributed significantly to PM2.5 in Beijing during the haze period. While in the sand period, the PM10 concentration in Beijing was mainly from the central of Inner Mongolia and western of Liaoning province.
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