天津市夏季重污染天气过程PM2.5输送特征

利用环境监测、气象常规观测、美国国家环境预报中心(NCEP)再分析等资料,采用气溶胶激光雷达和HYSPLIT模式对2018年8月1—2日发生在天津市夏季的一次重污染天气过程进行分析。结果表明:地面弱气压场、低空逆温和偏东暖湿气流的输送为此次重污染形成提供了有利条件;气溶胶激光雷达分析表明,此次污染过程存在明显的水平输送和垂直分布特征,市区PM_2.5浓度升高除与水平输送有关,还与本地低空逆温造成的PM_2.5积累密切相关;HYSPLIT模式后向轨迹追踪研究表明,PM_2.5前期积累爬升阶段,气团主要来自偏南气流,200、500、1 000 m高度气团均有明显沉降,后期气团来向转变为较清洁的偏东暖湿气流,但同时带来大量水汽,造成天津市相对湿度的增加。此次污染过程前期是由于静稳天气形势导致PM_2.5积累,后期主要是天津市各区县之间PM_2.5的输送以及偏东暖湿气流输送水汽导致相对湿度的增加,污染进一步加重。

Transport characteristics of PM2.5 of heavy pollution weather in Tianjin in summer

Based on the data of environmental monitoring, conventional meteorological observation and NCEP reanalysis, aerosol lidar and HYSPLIT model were used to analyze one PM2.5 heavy pollution process in Tianjin in summer on Aug.1 and Aug.2, 2018. The results showed that the weak pressure of surface field, temperature-inversion layer in the boundary and east warm-humid airflow accelerated the accumulation of pollutants. Aerosol lidar analysis showed that the pollution process had obvious horizontal and vertical distribution characteristics. The increasing of PM2.5 concentration in urban area was not only related to the horizontal transport, but also closely related to the accumulation of pollutants caused by temperature-inversion layer in the boundary. The backward trajectory tracking by HYSPLIT model showed that in the early stage of cumulative climb of PM2.5, air masses mainly came from south, and the air masses had obvious settlement at 200, 500 and 1 000 m altitudes during the climbing phase of PM2.5 concentration. The eastward warm airflow brought the clearer air as well as a lot of moisture, which resulted the increasing of relative humidity during the later stage pollution. The static weather situation caused the accumulation of pollutants on the early stage, while and the transportation of pollutants between the urban areas of Tianjin as well as the increasing of relative humidity caused by the eastward warm humid airflow aggravated pollution on the later stage.