银川市冬季两次典型持续大气污染过程对比分析

为了探究边界层气象要素时空分布及其变化对银川市冬季持续污染天气过程污染物质量浓度变化的影响机制，利用2016年12月1日-2017年1月31日逐时空气质量以及地面和逐日定时探空气象观测数据，根据大气污染级别和过程持续时间，选取2016年12月9-21日（简称"1211过程"）和2016年12月29日-2017年1月9日（简称"1231过程"）为研究对象，采用统计和天气诊断相结合的方法，在分析比较银川市冬季两次典型持续污染过程演变特征及其与地面气象要素关系的基础上，探讨了大气环流、边界层要素变化对银川市冬季典型污染过程的可能影响机制.结果表明:①银川市冬季两次大气污染过程持续阶段，地面均以偏东或偏南风为主，风速较小，相对湿度较大，能见度较低；在污染清除阶段，地面风向转为西北或偏北风，风速较大，相对湿度较小，能见度较高.②当冬季欧亚大陆中纬度区域500 hPa高空盛行纬向气流，850 hPa高度上银川市受反气旋环流和暖温度脊控制，并且有弱暖平流从西南部向北输送时，银川市易出现静稳型持续污染天气.③冬季银川市持续大气污染过程中，ρ（PM_2.5）与风速呈负相关（R平均值为-0.326），与相对湿度呈正相关（R平均值为0.688），与能见度呈显著负相关（R平均值为-0.905），与边界层高度呈较显著负相关（R平均值为-0.575）.④银川市冬季静稳型持续污染天气主要分为弱西北和平直西风气流型两种，弱西北气流型具有近地面层逆温弱，污染物积累慢，清除快的特征；平直西风气流型具有近地面层逆温强，污染物积累快，清除慢的特征.研究显示，冬季银川市上空500 hPa高度盛行纬向气流，地面主导风向为偏东或偏南风时，随着地面相对湿度增大、近地层风速减小、大气垂直上升运动减弱、边界层高度降低，大气中ρ（PM_2.5）将迅速升高，银川市易出现以PM_2.5为首要污染物的静稳型持续污染天气. 

Comparative Study of Two Typical Continuous Air Pollution Processes in Yinchuan City in Winter

In order to explore possible influence mechanism of pollutant concentration changes during continuous pollution in winter in Yinchuan City, the temporal and spatial distribution of meteorological elements in the boundary layer were analyzed using hourly air quality and surface meteorological observations and daily sounding observations at 08:00 and 20:00 from December 1st, 2016 to January 31st, 2017. Based on the level and duration of the air pollution process, from December 9th to 21st, 2016 (referred to as the 1211 process) and from December 29th, 2016 to January 9th, 2017 (referred to as the 1231 process) was selected as the two research objects. Then, the evolution characteristics of two typical processes and their relationship with ground meteorological elements, atmospheric circulation and boundary layer elements were analyzed and discussed using a combination of statistical and weather diagnostic mothed. The results show that:(1) During the continuous stage of two typical pollution processes, the easterly or southerly wind prevailed on the ground, with the low wind speed, the high relative humidity, and the low visibility. But in the stage of pollution removal, the wind turned to the northwest or northerly wind, with high wind speed, low relative humidity, and high visibility. (2) Yinchuan City was prone to static and stable continuous pollution weather when the latitudinal airflow was prevailed at 500 hPa over the mid-latitudes region of Eurasia in winter, and the anticyclonic circulation and warm temperature ridge was controlled at 850 hPa, and the weak warm advection is transported to from southwest to the north. (3) In the process of winter air pollution in Yinchuan City, ρ(PM_2.5) was negatively correlated with wind speed (R average value was -0.326), visibility (R average value was -0.905), and the boundary layer height (R average value was -0.575), but positively correlated with relative humidity (R average value was 0.688). (4) The winter static and stable air pollution weather in Yinchuan City was mainly divided into the weak northwest and straight west airflow type. The weak northwest airflow type had the characteristics of weak anti-temperature near the ground layer, slow accumulation of pollutants and fast removal. But the straight west airflow type had the strong anti-temperature near the ground layer, fast accumulation of pollutants and slow removal. In summary, when the zonal airflow prevails at the altitude of 500 hPa over Yinchuan City in winter, and the ground dominant wind direct is easterly or southerly. When the relative humidity of the ground increases, the wind speed of the near-surface layer decreases, the atmospheric vertical motion weakens, and the height of the atmospheric boundary layer decreases, the ρ(PM_2.5) in the atmosphere increases rapidly. Yinchuan City is prone to the static and stable continuous air pollution weather with PM_2.5 as the primary pollutant.