宁夏典型工业城市2020年1月重污染过程特征及成因

2020年1月宁夏回族自治区典型工业城市石嘴山市出现了长时间、高强度PM_2.5污染天气.为揭示多因素综合作用对重污染天气的影响，在分析逐日空气质量指数（AQI）和常规污染物浓度变化特征的基础上，选取重点污染时段（2020年1月1—17日）为研究对象，基于环境空气质量数据、加密自动气象观测数据及NCEP再分析资料，采用统计分析、污染特征雷达图、气流后向轨迹聚类及天气诊断相结合的方法对重污染过程特征和成因进行分析.结果表明:①2020年1月1日、3日石嘴山市重污染天气主要受燃煤、工业（钢铁、焦化）和机动车等高强度污染排放影响，PM_2.5主要来自一次源；9日重污染天气PM_2.5受二次颗粒物生成影响显著，本地扬尘也有贡献，ρ（PM_2.5）和AQI均达峰值，分别为216 μg/m3和266；其他时段重污染天气由污染物累积和混合造成.②乌海市及其周边污染气团跨区域传输是促使石嘴山市出现高强度PM_2.5污染天气的另一重要因素，当巴彦淖尔市—乌海市—石嘴山市为一致偏北气流、风速小于2 m/s时，易使乌海市及其周边污染气团向南扩散，石嘴山市ρ（PM_2.5）出现短时间爆发增长.③持续高湿静稳气象条件使污染天气长时间维持并加重，当欧亚大陆中高纬度500 hPa盛行纬向弱西风气流、近地面石嘴山市处在蒙古弱高压底部均压场、风向为弱偏北风或偏东风时，易形成持续性PM_2.5污染天气；当风速减至0.7 m/s、相对湿度增至78%时，污染加重.研究显示，此次持续PM_2.5重污染过程是本地高强度污染排放、二次颗粒物生成、区域传输与不利气象条件等因素综合影响和相互叠加的结果；当出现静稳、高湿等不利气象条件时，应加强对各类污染物排放的管控力度，同时充分利用石嘴山市及其周边加密自动气象观测资料，研判污染发展趋势和传输特征，及时开展与乌海市及其周边地区的大气污染联防联控. 

Characteristics and Causes of Heavy Pollution in Typical Industrial City in Ningxia in January 2020

In January 2020, a long-term and high-intensity heavy PM_2.5 pollution event occurred in Shizuishan City, typical industrial city, in Ningxia Hui Autonomous Region. This study analyzed the daily air quality index (AQI) and conventional pollutant concentration during the key pollution period from 1st to 17th of this event. Then the comprehensive effect of multiple factors on this heavy pollution event was revealed by using the data of environmental air quality, meteorological elements, and NCEP reanalysis and combining the method of statistical analysis, pollution characteristic radar chart, backward trajectory clustering, and weather diagnosis. The results show that: (1) The heavy pollution weather from January 1st and 3rd, 2020 was mainly affected by high intensity pollution emissions from coal, industry (steel, coking) and motor vehicles. PM_2.5 mainly came from primary sources. In addition to the local dust, the PM_2.5 on the 9th was mainly caused by secondary particles. The peak values of ρ(PM_2.5) and AQI were 216 μg/m3 and 266, respectively. Heavy pollution in other periods was caused by the accumulation and mixing of pollutants. (2) Another important factor contributing to the event was the trans-regional transmission of polluted air masses from Wuhai City and its neighboring. When the wind speed of Bayannaoer City-Wuhai City-Shizuishan City was uniformly northerly and less than 2 m/s, the polluted air masses Wuhai City and its surrounding diffused to the south, resulting in a short-term explosive growth of ρ(PM_2.5) in Shizuishan City. (3) The continuous high humidity and static weather conditions maintained and enhanced the pollution process. When the weak zonal westerly wind prevailed in the Eurasian continent at 500 hPa, Shizuishan City was controlled by the bottom average pressure field of the weak Mongolia high, and the wind direction was weak northerly or easterly, which was easy to form continuous PM_2.5 polluted weather. As the wind speed decreased to 0.7 m/s and the relative humidity increased to 78%, the pollution became more serious. In conclusion, the continuous heavy pollution process was the combined and superimposed result of local high-intensity pollution emission, secondary particulate matter generation, regional transmission, and adverse meteorological conditions. When there are unfavorable weather conditions such as static stability and high humidity, it is necessary to strengthen the control of the discharge of various pollutants. At the same time, make full use of the encrypted automatic weather observation data in Shizuishan City and its surrounding areas, study and judge the development trend and transmission characteristics of pollution, and carry out joint prevention and control of air pollution with Wuhai City and its surrounding areas in a timely manner.