Characteristics Of Temperature Inversion In Chengdu And Its Impact On Air Pollution

With the rapid development of China's economy,the process of urbanization is accelerating,and urban air pollution has a great impact on people's lives.As the largest city in Sichuan Province,Chengdu has achieved outstanding results in the prevention and control of air pollution in recent years.However,due to its large population,rapid economic development,and large exhaust emissions from motor vehicles,overall excessive emissions of air pollutants are still a reality One of the problems is that,especially in the fall and winter,when the temperature is reversed and other calm weather occurs,the process of heavy air pollution is very likely to occur.Therefore,studying the characteristics of temperature inversion in Chengdu and its relationship with air pollution is of great scientific significance for deepening the research and prediction of air pollution in Chengdu.This article uses the temperature sounding data below 500h Pa twice a day from08:00 and 20:00 Beijing time in 2008-2018 in Chengdu area,the air quality index of2014-2018 and 6 conventional pollutants(PM_2.5,PM₁₀,SO₂,CO,NO₂ and O₃)daily average data of mass concentration,studied the air quality index of Chengdu area from 2014 to 2018 and the seasonal and interannual changes of six conventional pollutants,and analyzed the frequency of temperature inversion from 2008 to 2017,The number of layers,thickness and strength characteristics,and in-depth analysis of the relationship between the number of inversion layers,thickness and strength and atmospheric pollution,in order to provide a new scientific basis for the prediction and prevention of air pollution in Chengdu.The main conclusions are as follows:(1)Except for O3,the monthly average mass concentrations of AQI at 08:00 and20:00 and the five conventional pollutants change in a"U"shape throughout the year,showing the characteristics of high winter and low summer.From 2014 to 2018,the average annual mass concentration of AQI and 6 conventional pollutants showed a downward trend,which shows that Chengdu has produced significant results in the treatment of air pollution,and air pollution has generally improved.On cloudy days and sunny days,the concentration of various pollutants is higher and the pollution is heavier.The temperature inversion frequency,layer number,thickness and intensity are larger,and the characteristics of temperature inversion are more significant.On precipitation days,especially when the rainfall is moderate or heavy,the inversion frequency,layers,thickness and intensity are all small.In addition,precipitation has a certain wet removal effect on pollutants.Among them,the wet removal effect on pollutants is the best when there is moderate rain.(2)The monthly average frequency at 08:00 and the average monthly thickness at 20:00 are"U"shaped throughout the year,and the intensity of ground inversion at08:00 and 20:00 is throughout the year It also shows a"U"-shaped change,both of which are large in winter and small in summer.The monthly average frequency,number of layers,thickness and intensity of the inversion of the lower troposphere at08:00 and 20:00 also show a"U"shape throughout the year,with large winters and small summers.In recent years,the frequency of ground-inversion inversion has increased compared with the previous years.The number of ground-inversion and low-troposphere inversion layers has also increased,and the frequency of multi-layer inversion has also increased compared with previous years..In recent years,the thickness of the inversion temperature and the inversion temperature of the lower troposphere have decreased slightly compared with the previous years,and the inversion intensity of the inversion temperature and the lower troposphere has a trend of increasing year by year.(3)The air quality ranges from excellent to severe pollution,and the inverse temperature layers,thickness and strength corresponding to this are increasing.Except for O₃,the number,thickness and intensity of temperature inversion layers are positively correlated with AQI and the mass concentration of various pollutants,which shows that the characteristic elements of temperature inversion and Pollution is closely related,the greater the value of each temperature inversion factor,the more serious the pollution.Each temperature inversion element is negatively correlated with O3 to a certain extent,which may be due to the fact that atmospheric junction is relatively stable in the presence of temperature inversion,and oxygen atoms in the atmosphere cannot fully contact with oxygen molecules to generate ozone molecules.(4)In the process of heavy pollution in winter in Chengdu,the air pollution corresponding to the low-groove weather type is more serious,with the southwest low-pressure type having the greatest impact.When the weather type is a low-slot type and the main wind direction is southwest,south and west,heavy pollution weather is prone to occur.When there are many layers of temperature inversion in the daytime and the thickness and intensity are large,it is difficult for the gaseous pollutants to diffuse.In the daytime,the number and thickness of the inversion temperature in the lower troposphere have a positive correlation with the mass concentration of various pollutants,while the number,thickness and intensity of the temperature inversion layer at night are positively correlated with the mass concentration of particulate pollutants.When the total number of inversion layers during the day is larger and the thickness is larger,the more the diffusion of various pollutants can be suppressed,causing the accumulation of pollutants,thereby increasing air pollution,AQI has a certain degree relative to the inversion layer and the inversion thickness The phenomenon of hysteresis also corroborates the effect of temperature inversion on the accumulation of pollutants.It is particularly worth mentioning that the positive correlation between temperature inversion layers and air pollution is more significant than the temperature inversion thickness and intensity.