| The Beijing-Tianj in-Hebei region is one of the most economically developed regions in China.However,in recent years,with the rapid development of China economy and the acceleration of industrialization and urbanization,the Beijing-Tianj in-Hebei region has become one of the most polluted regions in China.With the increasing regional pollution,it is necessary to make a comprehensive and stereoscopic observation of the lower tropospheric atmosphere at different altitudes and regions,and to obtain the most direct data of the concentration distribution of atmospheric pollutants in different regions and altitudes.This study was carried out by tethered balloon platform.Based on the wind tunnel pressure chamber experiments,two quality control measurements,which were the pressure calibration of gas instruments and the isokinetic sampling were achieved.The vertical distribution of atmospheric pollutants in the process of heavy pollution below 1000 m height were studied.The vertical distribution characteristics of atmospheric pollutants in the atmospheric boundary layer at sunrise morning and sunset evening were studied.The following conclusions can be drawn from the direct variation of vertical observation:(1)According to the vertical observation of the tethered balloon platform(0-1000m from the ground,i.e.atm-900 mbar),the pressure calibration of the gas detection instrument was carried out.The pressure calibration method of gas instrument was designed and applied independently.The pressure calibration experiment of gas instrument used in vertical observation was carried out,and the pressure correction equation was obtained.This method solved the pressure calibration problem of observation platforms like tethered balloons or drone with limited load for the first time.(2)The vertical distribution of atmospheric pollutants and atmospheric structure below 1000 m in Wuqing area had obvious diurnal variation.Within 2 hours after sunrise,the atmospheric boundary layer was divided into three layers:stable boundary layer,residual layer and roll interlayer.2 hours after sunrise,it evolved into four layers and formed mixed layer on the surface.The nocturnal low-level jet appeared at the height of the stable inversion layer and changed with the stable boundary layer after sunrise.Although PM2.5 and NO_x both accumulated in the stable boundary layer,the degree of NO_x accumulation was stronger,while PM2.5 was relatively weak.Generally speaking,it mainly accumulated below the volume interlayer(within the boundary layer).O3 was evenly distributed in the remaining layer,with high and stable concentration,which was the result of daytime ozone residue.In the afternoon,the atmospheric junction below 1000 m was a mixed layer with strong atmospheric turbulence and vertical convection,making the vertical distribution of PM2.5,O3 and NO_x uniform.The stable boundary layer began to develop.PM2.5 and NO_x gradually accumulated near the ground.The accumulation of NO_x was stronger than PM2.5.(3)During the pre-heavy-pollution period,the atmospheric stratification was unstable and the vertical distribution of PM2.5,NO_x and was uniform,which indicated obvious vertical convection and favourable diffusion condition.The value of PM2.5/PM10 was 0.60-0.80 at an altitude below 800 m while it was above 0.90 at an altitude of 800-1000 m.During the heavy-pollution period,atmosphere near ground was divided into four layers:convective boundary layer(0-150 m above the ground),thermal inversion layer(150-370 m),mixing layer(370-500 m)and free atmosphere(above 500 m).NO_x tended to accumulate below the boundary layer.The downward O3 from high-altitude was hindered by strong mixing layer,and form a small O3 peak at 500 m.PM2.5,which was mainly consist of accumulative mode aerosols with the size of 0.5-1μm,accumulated not only near the ground but also in the inversion layer with bimodal distribution(peaks at 150 and 370 m).Under unfavorable diffusion condition,the accumulation of vehicle exhausts,village residents heating emissions and the secondary particles were the key factors for the formation of heavy pollution during this period. |
