Abstract: The hourly air quality index （AQI） and six major pollutants monitoring data of 14 national control stations from January 5 to 8, 2019, meteorological observation data, wind profile radar data and FY-4 satellite data of corresponding periods provided by Hunan ecological environment monitoring center were used to deeply analyse a severe pollution weather process in Changsha city in early January 2019, combined with the HYSPLIT4 backward trajectory. The results showed that the severely polluted weather process in Changsha city was a process of taking PM2.5 as the primary pollutant. The backward trajectory analysis showed that the tracks of the air masses in the middle and lower layers were the same. Affected by the superposition of air masses, the pollutant of long-distance transmission from central Henan province affected Changsha city, which was one of the main pollution sources. In the accumulation and outbreak stage, the stable low and medium cloud was the main part, and TBB was more than -10 ℃. According to the analysis of wind profile data in the outbreak stage, pollutants were transported to Changsha city with the northeast air flow, and the input of external sources was dominant. From 850 hPa to 700 hPa, there were obvious inversion layer or isothermal layer in the middle and low relative humidity in the upper air, which were favorable meteorological factors for this heavy pollution weather.

Key words: heavy pollution weather, pollution characteristics, transmission characteristics, diffusion conditions, meteorological conditions, Changsha city