A Research On Winter Aerosol Vertical Distribution Characteristics In Fengxian, Shanghai

Vehicle-based tethered-balloon observation platform was used for vertical observation of atmospheric aerosol from 150 to 1,000 m during December 2013 in Fengxian, Shanghai.Comprehensive analysis of aerosol vertical distribution of different pollution levels and typical polluting weather conditions provided scientific evidence for Shanghai air pollution early warning and the formulation of the controlling countermeasure, as well as the basic data for investigating pollutant transfer. The analysis shows the following results:The analysis of aerosol number concentration, diameter, and mean spectrum distribution of different pollution level shows that:1) The vertical distribution characteristics of number concentration and particle diameter: ① In clean days(AQI below 100), in the temperature inversion layer, the number concentration increases with altitude; In non-inversion layers, the number concentration decreases with altitude. ②In the noon time of mild pollution days(AQI between 100 and 150), the profiles of number concentration and diameter distribution were volatile but the vertical distribution of number concentration and diameter were uniform; the vertical distribution of number concentration had a positive correlation with relative humidity while the vertical distribution of diameter vertical distribution had a negative one. ③In moderate pollution level(AQI between 151 and 200), the diameter was in mean distribution. The number concentration increased with altitude in the temperature inversion layer, while the vertical distribution of number concentration had positive correlation with relative humidity in the non-inversion layer. ④ In heavy pollution condition(AQI above 200), the diameters of aerosol particles were within the range of 0.95 μm and 1.03 μm, the vertical distribution was even. The number concentration vertical distribution was layered and closely related to relative humidity above 700 m.2) Aerosol pollutants between 150 m and 1,500 m in different pollution levels mainly consist of fine particles of which diameter below 2.5 μm. The mean spectrum distribution of different pollution level showed in mono-peak form. The peak diameter is around 0.9 μm. The width of spectrum decreases in the order of clean, moderate, mild,heavy pollution conditions.3) During heavy pollution, local source pollution played the main role of aerosolpollutants, north-northwest and northwest air mass transfer also made contribution to the pollution.Combined with the daily aerosol vertical variation characteristics of typical pollution conditions, the following points were worked out:1) The number concentration of aerosol decreased as altitude increased and showed unequal distribution and layered in the morning.In the noon, the number concentration evenly distributed from 150 to 1,000 m, the profile varied in a narrow range. As a result of the influence of the inversion layer and air mass transfer, the number concentration in high altitude increased as altitude increased in the afternoon. In the evening, the vertical distribution was seen to have close relationship with the altitude of mixture layer, night boundary layer and the distribution of the residual layer.2) The inversion layer had influences on vertical transfer of aerosol particles, made discontinuous vertical distribution within the layer and particles concentrated in the layer.Without an inversion layer, the maximum number concentration appeared near the ground.3) The vertical distribution was influenced intensively by the high-altitude wind field. As upward flow and downward flow vertical alternation occurred frequently, the vertical transfer was active and formed uniform mixed aerosol.4) The Fengxian aerosol spectrum(0.5-5μm) showed mono-peak distribution, with a peak diameter around 0.9 μm, mainly consisted of fine particles; the concentration variation of particles with peak diameter fit with the change of number concentration of aerosol.