Study On The Scale Effect Of PM_2.5 Concentration For City Based On Fractal Theory

Economic development has brought great pressure on the atmospheric environment,the pollution is significance serious.With the living conditions and the environmental awareness of the people have been improved,PM_2.5 has been given more attention as an primary pollutants of air pollution.At the same time,it has attracted many scholars to study the laws of PM_2.5 evolution,However,PM_2.5 pollution is a complex reflection of the interaction of many factors,the dynamic characteristics of PM_2.5 pollution evolution can not be accurately,clearly and comprehensively described by traditional time series analysis method.The present paper is aimed to study the temporal scaling properties of the hourly PM_2.5 average concentration series?from 1 January,2015 to 31 December,2016?in Changsha based on the fractal theory.First,The relationship between PM_2.5 concentration and meteorological factors in Changsha was analyzed based on the meteorological data.It was found that the greater the wind speed,the stronger the diffusion dilution ability of PM_2.5 pollutants,the smaller the wind speed,the lower the diffusion ability of PM_2.5 pollutants,which could easily lead to the accumulation of pollutants.The effect of mean air pressure on PM_2.5 was different in different months.With the increase of relative humidity,the concentration of PM_2.5 increased firstly and then decreased.Second,The correlation analysis between PM_2.5 concentration and gaseous pollutants are investigated.The results show that There was a good correlation between PM10 and PM_2.5,PM_2.5 and NO2 were positively correlated,and PM_2.5 and NO2 were easy to overlap pollution.When NO2 concentration increased,the concentration of increased with the increase of PM_2.5 concentration.The negative correlation between the concentration of PM_2.5 and O3 in Changsha was mainly due to the difference of the source and reaction mechanism between PM_2.5 and O3.Thirdly,The variation of PM_2.5 concentration at different time scales was discussed.The diurnal variation trend of PM_2.5 concentration in Changsha city was basically the same in 2015 and 2016,showing the first rising,then falling and then rising and falling.The monthly variation: PM_2.5 exceed the standard monthly daily and monthly variations in the concentrations are basically the same,showing intermediate low,high on both sides of the“U“ type,namely the spring and summer low,then the autumn and winter high.Seasonal variation: the winter in is obviously higher than that in spring,summer and autumn three seasons Changsha.Finally,the law of change and the structure character of PM_2.5 series in Changsha are investigated by the DFA means.We study the structure character of the PM_2.5 series from 2015 to 2016,and indicate that the PM_2.5 sequence have the characteristics of long-term persistence and the statistical properties of fractal distribution.Further more,we study the fractal structure in different time scales by DFA analysis,and depict the scale effect during the process of evolution about PM_2.5 concentrations,and to explore the internal dynamic mechanism of the evolution of PM_2.5,It is considered that the long-term persistence control the variety of PM_2.5 concentration.