Characteristics Of Atmospheric Boundary Layer Structure And Its Effect On Air Pollution Over Nanjing Xianlin

Atmospheric boundary layer(ABL)refers to the lower troposphere,which directly affected by the ground.Turbulence is the main feature of the ABL,and the complex meteorological changes in the ABL affect the evolution of the whole atmosphere,which has significant impacts both on the diffusion or removal of pollutants and the stability and change of global climate.It is of great significance for effectively formulating air pollution control strategy to study the structure of ABL in Xianlin of Nanj ing and its impacts on air pollution,which is also helpful to understand the characteristics and evolution of air pollution.In this study,the radiosonde observation experiments were carried out twice with Automatic Atmospheric Data Acquisition System(ADAS).The date of the two experiments was from December 26,2013 to January 10,2014(15 days)and from June 6,2014 to June 24,2014(19 days).On this basis,the following three studies were carried out:(1)Study the vertical features of meteorological elements,inversion,and the atmospheric mixed layer of the ABL in different time in study area by analyzing the observed data with height change about wind,temperature,humidity,pressure and other meteorological elements.(2)Study the influence of macro meteorological conditions on the structure of ABL based on the large scale meteorological data(the surface weather chart and the high altitude circulation).(3)Study the effects of the ABL structure on the concentrations of the major air pollutants(such as PM2.5?SO2?NOx and O3)based on the data of the air pollutant concentration in the same period..The results are:(1)The average height of mixed layer in summer was 1200 m and was obviously higher than that in winter,which was 700 m.The inversion layer mainly occurred at night and most of them were the ground inversion.In winter,the average thickness of ground inversion temperature was 107.5 m and the inversion intensity was 1.14?/100m,while they were 190.48 m and 0.7?/100m in summer.Therefore,the ground inversion temperature was strong intensity and low thickness in winter,but weak intensity and high thickness in summer over Xianlin,Nanjing.(2)Xianlin was controlled by the average pressure and high pressure in winter.The average mixed layer height was 400m under the control of the average pressure while was 825 m under the control of the high pressure.In winter,the ABL structure was stable and the mixing layer height was low when the cold high pressure system moved slowly.Xianlin was controlled by the subtropical high pressure and the average pressure in summer.The average mixed layer height was 950 m and 1000 m under the control of the subtropical high pressure and the average pressure,respectively.The structure of the ABL changed rapidly when under the control of the subsidence of the typhoon,but under the control of the low pressure trough,the height of the mixed layer was low and the relative humidity was large,also the wind speed changed greatly.(3)The concentration of air pollutants and the mixed layer height showed a good anti-correlated in winter,that is,the change of pollutant concentrations and the ABL structure tend to be synchronized;but the anti-correlation was weak in summer.This may be due to the rapid changes of meteorological conditions in summer and the horizontal diffusion in the ABL is obvious,which weakened the correlation.The diurnal variation of the ABL showed different impacts on the surface concentrations of different pollutants.For SO2,due to the high point source,the high concentration area was easily formed at night.When the mixed layer was highly developed to the high altitude smoke flow in the morning,the high concentration of SO2 was rapidly brought to the ground by the ABL and formed a high concentration value on the ground.NO2 was mainly from the mobile emission source,and the effect of vertical diffusion was better because of ABL changes.Therefore,the concentration of NO2 and the mixed layer had a good anti-correlation and the concentration reached the lowest at 14:00.For O3,the peak concentration occurred at about 14:00 in the afternoon due to the obvious effect of solar radiation.