| This paper first analyzes the temporal and spatial distribution characteristics of pollutants in Yunnan,and uses statistical analysis methods to explore the correlation between pollution concentration and meteorological factors.Secondly,the SOM clustering method is used for weather classification to analyze the differences in air quality and meteorological causes under different weather types.Finally,all the Kunming quasi-stationary front(KQSF)processes in the study period were determined by objective method.The characteristics of meteorological elements in the frontal process were analyzed,and the influence of KQSF on air quality was discussed.The main findings are as follows:The daily variation of PM10,PM2.5,NO2,SO2 and CO concentration in each city showed a bimodal type,with the peak value at 10:00 in the daytime and the peak at 21:00 in the night.The daily variation of O3 is unimodal type,and the peak values are around 15:00.The concentration of particulate matter has obvious cycle variation,the working day is higher,the weekend is lower,the annual change is higher in winter and spring,and lower in summer and autumn.The annual change of 03 concentration is higher in winter and lower in spring.When the wind speed is low,the pollutant concentration decreases with the increase of wind speed,but when the wind speed is greater than a certain value,the two are positively correlated.The wind speed thresholds of Kunming,Zhaotong,Honghe,Banna,Dehong and Lijiang stations are respectively 2.2m/s?3.7m/s?2.5m/s?1.9m/s?2.2m/s?3.7m/s.The concentration of pollutants is the highest in a certain interval,and the temperature increases and the concentration of particulate matter decreases after exceeding this temperature range.With the increase of precipitation,the proportion of superior air quality increased,and the effect of precipitation on pollutants was obvious.There are 9 weather types obtained by SOM for weather classification.Characteristics of weather types with good air quality:Type 1 and Type 2 are affected by the southwest and southeast monsoon in summer,and are clean and humid air currents from the tropical ocean surface.Type7 is a stronger low pressure to development at lower layer,the atmospheric stratification is unstable convection is strong,and there is a warm and humid airflow in the southwest and southeast.The ty'pe 6 is from the southeast airflow of the tropical ocean surface,and the low-level air pressure is high.If there is no local source discharge,it is not easy to produce polluted weather;Characteristics of weather types that are likely to cause air quality degradation:Types 8 and 9 are affected by low trough in winter,and westerly winds bring out foreign pollutants,and low-level cyclones develop.Convergence of airflow is conducive to converging pollutants.In the Type 3,Yunnan is in a high-pressure control zone.The atmospheric stratification is relatively stable.At the same time,the westward airflow transports the in-situ pollutants.The type 4 is affected by the cold air in the north,and the westward dry airflow is from the inland area.The precipitation is scarce and the ground pressure is also low.This configuration is prone to pollution.Type 5,Yunnan is in the negative vorticity advection zone after the high-altitude trough.The ground pressure anti-cyclone develops with high stability.The main airflow comes from the northern part of China and is easy to transport pollutants.On average,about 21.3%of the time has the existence of KQSF.Ahead of the front,the potential pseudo-equivalent temperature is higher.The prefrontal area is the west wind,after the front area is the north wind.The concentration of particles in the front process is higher.The boundary layer height of the front process is low,which is not conducive to the vertical diffusion of pollutants.The stability of the frontal process is relatively high compared to the non-frontal process,and the polluted weather is more likely to occur during the frontal process. |
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