基于多源资料天津一次雾-霾过程的边界层特征

Boundary layer characteristics of fog-haze in Tianjin based on multi-source data

为探究雾-霾过程的边界层特征,选取天津市2019年12月7~10日一次严重的雾-霾典型过程,采用常规自动气象站资料、环境小时浓度资料、以及微波辐射计、风廓线雷达、气溶胶激光雷达等多种观测资料及WRF-Chem源追踪方法对此次污染过程进行综合分析.结果表明,此次雾-霾过程可明显分为雾生成、雾与霾交替、霾、霾消散等4个阶段;雾-霾天气与大气温度层结密切相关,伴随着逆温生成,相对湿度和液态水含量最大增长速率分别达13.44%/h和0.013g/(m^(3)·h),呈爆发性增长,相对湿度快速增至92%,微波辐射资料可较好预报雾的生成;雾与霾交替出现阶段雾天气改变了边界层结构,雾层内大气呈中性状态,相对有利于污染物在雾区内扩散,PM_(2.5)高浓度主要出现在边界层400m以下,雾顶持续逆温抑制了污染物向上层大气扩散,造成雾区内污染物浓度加重,地面PM_(2.5)质量浓度为135~223μg/m^(3),维持中度-重度污染;雾-霾天气与垂直风场有较好的对应关系,雾与霾交替出现阶段存在低风速和较大风速(西南风带来充沛水汽)两种有利于雾维持的情况,雾顶逆温层以上风速为6~12m/s,雾层内为1~2m/s,雾的存在不利于近地面空气质量的改善;此次雾-霾过程天津本地源排放贡献为36.1%,区域输送贡献为63.9%,整个过程表现出明显的区域输送特征.

In order to explore the boundary layer characteristics,the multi-source observation data such as automatic meteorological station data,environmental hourly concentration data,microwave radiation data,wind profile radar,aerosol lidar and WRF-Chem source tagged method were used to analyze a typical fog-haze episode in Tianjin from December 7 to 10,2019.The results showed that:The fog-haze process can be clearly divided into four stages of fog formation,fog and haze alternation,haze,and haze dissipation.Fog-haze weather was closely related to atmospheric temperature stratification,with the generation of temperature inversion,the maximum growth rate of relative humidity and liquid water content reached 13.44%/h and 0.013g/(m^(3)·h),respectively,showing an explosive growth up to 92%of the relative humidity,and the microwave radiation data can better predict the formation of fog.In the stage of fog and haze alternation,fog weather changed the structure of the boundary layer.The atmosphere in the fog layer was in a neutral state,being relatively conducive to the pollutant diffusion in the fog area.The high value of PM_(2.5)concentration mainly occurred below 400m,and the continuous inversion at the fog top inhibited the diffusion of pollutants to the upper atmosphere,resulting in the aggravation of pollutant concentration in the fog area and an increase in surface PM_(2.5)up to 135~223μg/m^(3)near to ground,maintaining moderate-severe pollution.There was a good relationship between fog-haze weather and vertical wind field.In fog and haze alternation stage,there were two situations,low wind speed and high wind speed(the southwesterly wind brought abundant water vapor),which are beneficial to the maintenance of fog.The wind speed was 6~12m/s above the fog top inversion and 1~2m/s in the fog layer.The existence of fog was not conducive to the improvement of air quality near the ground.During the fog-haze process,the local emissions contributed 36.1%to surface PM_(2.5) concentration in Tianjin,and the contribution of regional transport was 63.9%,demonstrating obvious regional transport characteristics of the whole pollutant process.