| Air quality characteristics and the main atmospheric pollutants from 2015 to2019 in Anshun were analyzed in this paper.MICAPS 4.2 was applied to discusse how synoptic situation affects the formation and development of a sporadic severe polluted cases from large scale weather situation.Traj Stat plugged in Meteoinfo Map was used to summarize the regional external polluted trajectories,the main routing area and the concentration of pollutants and identify the potential source-zones and its contribution to Anshun urban PM2.5in all polluted days.The relationship between local meteorological conditions and air quality index（AQI）was analyzed,and a multi-dimensional linear stepwise regression forecast model of AQI in four seasons was established.The prediction of the models was evaluated.The main conclusions are drawn following:（1）The pollution days in the urban area of Anshun from 2015 to 2019 were concentrated in autumn and winter,and the average AQI daily value fluctuated within the range of 25-125.PM2.5has exceeded the standard in each year,and the number of days as the primary pollutant increased year by year from 2015 to 2018,especially in winter（accounting for more than 40%）,becoming the most important air pollutant in Anshun.The daily mean concentration of PM2.5showed a trend of winter>spring>autumn>summer.Except for the weak correlation between PM2.5and CO in winter,it was significantly positively correlated with SO2,NO2,CO and O3in different seasons,and negatively correlated with average temperature,precipitation,average wind speed,average relative humidity and average total cloud cover.（2）During a heavy pollution in Anshun,the stable synoptic situation of the ground,500 hPa,700 hPa and 850 hPa in the upper air created favorable conditions for the deposition accumulation of PM2.5transported to Anshun,and the radiation inversion layer（thickness of 10-22 hPa,temperature ranging from 1 to 4℃）formed in the process aggravated the pollution,and the convective disturbance increasing atmospheric instability was obvious until 8:00 on the 16th,which promoting the mixing and dilution of PM2.5.（3）The number of clustering tracks of air mass movement in four seasons in Anshun was 6,6,5 and 4,respectively.The pollution tracks were mainly in autumn and winter,with 56 pollution tracks（average concentration 95.79μg/m3）and 91pollution tracks（88.09μg/m3）,respectively.PM2.5pollution transport channels mainly passed through northwestern Guangxi,southern Guizhou and northeastern Guizhou.In 2017 and 2018,more PM2.5was imported into Anshun with the air mass,mainly passing through the border area between northern Guizhou and Guangxi.（4）With the increase of the study height,the daily track of exceeding PM2.5has a stronger impact on long-distance transport.The track in the northeast of Guizhou was the main pollution transport path.The high-concentration external transport（WPSCF>0.5）was mainly near the surrounding areas.The WPSCF>0.9 region at500 m was more than that at 10 m and 1500 m.The high concentration contribution area（WCWT>75μg/m3）extended to the southwest with the increase of the study height,and the contribution of high concentration PM2.5pollution transported from outside the province was small.（5）The AQI of the four seasons increased with the increase of sunshine hours and the previous day’s AQI value.In spring and winter,the air quality decreased with the increase of air temperature type factor,and in autumn and winter,the AQI increased with the increase of air pressure type factor.The higher the daily maximum temperature in summer and autumn,the worse the air quality.（6）The forecast effect of the four seasons AQI model was evaluated.The grade score was 68%-85%,the accuracy was 70%-85%,NMB was-0.5%-7%,NME was 15%-32%,RMSE was 8.5-17%,and R was 0.708-0.925.The prediction effect in spring and summer was better than that in autumn and winter.All AQI forecasting models can meet the practical application requirements. |
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