2020年西双版纳持续重霾天气成因和来源分析

The Causes and Sources of a Persistent Heavy Haze Pollution Event in Xishuangbanna Aarea during 2020

利用常规气象观测资料、环境监测站点的空气污染物浓度监测资料、欧洲中心(ECMWF)提供的ERA-5逐时0.25°×0.25°再分析资料和NOAA研发的Hysplit后向轨迹模式,分析了2020年3月29日-4月5日低纬高原的西双版纳地区持续性重度霾空气污染事件的特征、气象成因和污染物颗粒主要来源。结果表明:①重度霾污染期间,AQI值及PM_(2.5)浓度值有显著日变化特征,表现为白天低、夜间高。②冷空气势力偏弱,脊前暖平流使中低层大气增温,有利于西双版纳地区大气层结的稳定,无明显水汽输送带,整个过程空气湿度较低,连续8 d重度霾污染并未出现传统上高湿的气象霾特征。稳定的大气层结和逆温层削弱了大气在垂直方向上的对流交换。③受均压场控制,地面和低空风速小,较低的混合层厚度和较小的通风系数等共同作用,使得污染物颗粒在水平和垂直方向上扩散受到抑制,导致污染物颗粒聚集。④各污染物浓度值与MODIS/Terra卫星反演东南亚境外火源点数有显著相关性,其中火源点个数与AQI正相关高达0.5。⑤Hysplit后向轨迹模式表明此次重霾污染过程中颗粒物的可能来源主要是缅甸马圭、曼德勒和东枝境外的输入型累积传输。西双版纳位于低纬高原地区,受地形影响,污染物积聚在景洪城区及周边澜沧江河谷地带之后,很难通过水平输送离开,这也是造成此次连续重度霾污染事件的重要原因。

Based on conventional meteorological observations from Meteorological Bureau of Jinghong,the air pollutant mass concentration data from Jinghong Environmental Protection Bureau,and reanalysis data of ERA-50.25°×0.25°from MFECW(European Centre for Medium-Range Weather Forecasts)and the Hpsplit backward track model from NOAA(National Oceanic and Atmospheric Administration),the characteristics and causes of a Persistent heavy pollution event in Xishuangbanna region on March 29 to April 5,2020 were analyzed.The results show that the diurnal variation of AQI(Air Quality Index)and PM_(2.5) concentration were lower in daytime and higher at night.The cold air is weak and prevailing zonal westerly winds during the pollution period at Low latitude plateau area.Meanwhile,warm advection ahead of a ridge that continuously moves eastwards greatly impacts on the increase of temperature in the middle and lower levels of atmosphere,which is favorable for the formation of the stable atmospheric stratificanon.There is no apparent vapor transfer and no classic wet haze feature.The convection and diffusion has been weakened by stable temperature stratification and atmospheric circulation.The horizontal and vertical diffusion is reduced by lower mixing layer height and surface ventilation coefficient,which leads to increased concentrations of pollutants.There is positive correlation between the pollutant concentration and the numbers of ignition sources in Southeast Asia from MODIS/Terra satellite monitoring and retrieval.The correlation coefficient of AQI and the number of ignition is as high as 0.5.Furthermore,based on the Hysplit backward track model and the fire point data at that time,the influencing factors of heavy pollution weather in Xishuangbanna from March 29 to April 5,2020 were analyzed.According to the analysis,the pollutants are mainly imported from Maqui Mandalay and East Branch,Myanmar.In addition,Xishuangbanna is located in Lancang River Valley.Such a local surrounding terrain blocks the subsequently horizontal transport of air pollutants after accumulcting in xishuangbanna region,which is also a major reason for the occurrence of this pollution event.