Construction And Application Of A Winter Air Pollution Potential Model In Chengdu

The potential of air pollution is a qualitative or semi-quantitative analysis of the future atmospheric environmental quality according to the current meteorological conditions.It is a manifestation of the comprehensive diffusion capacity of the atmosphere,and provides a solid theoretical basis and technical support for the prediction and analysis of regional air quality change trends,which plays a key role in the early warning and control of heavy pollution weather.Thus,it has always been one of the key and difficult points in environmental air quality man agement.In view of the lack of research on Chengdu's winter air pollution potential and the vague formation mechanism of regional pollution,this paper uses the environmental meteorological data from December 2013 to February 2018 to construct Chengdu's winter pollution potential analysis model,combined with Mie scattering lidar detection data from December 2013to February 2014,on the basis of the research on the mixed layer height and relative humidity probability density,and Copula joint distribution method.The main research conclusions include the following aspects:(1)The pollution in the study area has been decreasing in the past five years in winter,but the problem of particulate matter pollution in winter is still very prominent,which significantly affects the rate of air quality exceeding the standard in the r egion.Relative humidity and mixed layer height are the main factors affecting pollutant diffusion in the winter static and stable climate.Based on this,the feasibility of using mixed layer height and relative humidity as meteorological factors for air pollution potential prediction is studied.(2)Based on Logistic curve algorithm,the time series of mixed layer height at the same time is inversed,and the variation characteristics of mixed layer height and its air pollution effect are systematically analyzed.The results show that the mixed layer height is(324±87)m during the observation period in the study area,and presents the daily variation characteristics of"single peak-valley type";According to the positive deviation form of the hourly mixed layer height empirical probability density,the lognormal probability density function has obtained the best fitting effect(through KS test),which can be used to characterize the probability density characteristics of hourly mixed layer height in Chengd u's winter.By analyzing the response relationship between the mass concentration evolution of PM_2.5 and the height of the mixed layer,this paper has found that the threshold value of the height of the mixed layer corresponding to the fine particle pollution in the research period is 475 m;(3)The relative humidity in the observation period of the study area is(83±16)%,and its hourly mean value presents the daily variation characteristic of"single valley type";Through the comparison of four probabilit y density functions,it is found that Pearson ? function can best fit the forward biased form of hourly relative humidity probability density(passing KS test);The relative humidity threshold of fine particle pollution in the study area is 88%,and this threshold corresponds to the explosion point of aerosol moisture absorption gro wth intensity.(4)Copula connection function is systematically combined with relative humidity and mixed layer height probability density to make it a joint probability density,and combined with PM_2.5 mass concentration data to find classification criteria of different pollution potential types.Based on the criteria,the winter pollution potential in the research area can be preliminarily classified into good,medium and poor levels,and the diagnosis results of the model are basically consistent with the actual situation.