2018年初冬成都市重污染事件气象条件分析

Analysis of Meteorological Conditions for Heavy Pollution Events in Chengdu in the Early Winter of 2018

2018年12月11日~22日,成都地区发生了一次长达12天的重污染过程。本文利用中国生态环境部提供的成都市7个站点逐时环境监测资料、成都市温江气象站观测资料、怀俄明大学提供的温江站探空资料以及NOAA提供的2.5?×2.5?NCEP/NCAR再分析资料,对此次重污染过程的污染特征、污染气象参数特征、850hPa和925hPa水平风速特征、大气环流背景进行了分析。结果表明,细颗粒物是此次重污染过程的首要污染物,污染过程后期较前期严重;四川盆地高空维持平直西风或受脊前西北气流控制,导致垂直运动弱、低空出现暖平流使逆温层底部高度降低,因此限制了混合层高度,使大气环境容量减小、850hPa以下大气水平风速较小是污染物累积的三大关键因素;850hPa、925hPa等压面上水平风速对污染物的累积和清除具有很好的指示意义;此次重污染过程中15日有一次冷空气活动,但是持续时间短,并未改变静稳的大气层结,因此,重污染过程得以维持较长时间;21~22日高空极地冷涡引导冷空气南下,并配合地面冷高压从西方路径入侵成都,彻底改变低空静稳大气层结,是此次重污染过程结束的主要原因。

From December 11 to 22,2018,a heavy pollution process lasting for 12 days took place in Chengdu.Based on hourly environmental monitoring data from 7 sites in Chengdu,provided by Ministry of Ecological Environment of China,observation data of Wenjiang meteorological station in Chengdu,sounding data of Wenjiang station from University of Wyoming and 2.5?×2.5?NCEP/NCAR reanalysis data,pollution characteristics,meteorological pollution parameters,wind speed characteristics of 850 hPa and 925 hPa and atmospheric circulation background in this process were analyzed.The results showed that fine particulate matter was the primary pollutant in the heavy pollution process,and the pollution was more serious in the later stage than in the earlier stage.There were 3 key factors for pollution accumulation.First,the upper air of Sichuan basin maintained a straight westerly wind or was controlled by the northwest airflow in front of the ridge,resulting in weak vertical movement.Second,low-level warm advection reduced the bottom height of the inversion layer,which limited the height of the mixing layer and reduced the atmospheric environmental capacity.Third,atmosphere under 850 hPa horizontal wind speed was small.The horizontal wind speed on the isobaric surface of 850 hPa and 925 hPa was a good indication for pollutant accumulation and diffusion.There was a weak cold front during the pollution weather process,but it was too weak to change stable atmospheric junction completely.Therefore,the pollution weather process lasted a long time.The main reason for the end of the heavy pollution process was that the upper polar cold vortex guided the cold air southward and coordinated with the surface anticyclone to invade Chengdu from the western path,completely changing the stable atmospheric junction of the lower atmosphere.