华北平原中西部地区秋季(10月)气溶胶观测研究

Observation Study of Aerosol over Mid-Western North China Plain in Autumn(October)

利用2010年10月在石家庄市区、邢台市区和柏乡县城进行的19架次飞机探测资料，研究了晴天、密卷云、高积云及雨后气溶胶粒子数浓度和粒子直径的垂直、水平分布和粒子谱分布特征。结果表明，这些地区的气溶胶粒子主要来源于下垫面输送，其输送效率受逆温、边界层风速切变等因素影响。近地面气溶胶浓度平均值为1000～3000cm-3，平均粒子直径为0．18～0．20μm，石家庄市区气溶胶平均浓度最低，邢台市区最高，柏乡县城气溶胶平均浓度值接近石家庄市区。近地面气溶胶浓度极大值为1075～4019cm。，且随高度呈负指数递减；高积云时呈分层分布，下层为直线分布，上层为负指数分布。受天气条件影响，小雨后气溶胶浓度最小，近地面均值为100cm-3；晴天、密卷云及高积云时近地面气溶胶浓度均值为1000cm。。逆温层和光照强度日变化影响气溶胶垂直分布的日变化，晴天，日出前后近地面气溶胶浓度最高，均值为1799cm-3，近地面气溶胶累积易造成地面大气污染；12：00（北京时，下同）近地面气溶胶浓度最低，均值为706cm-3，垂直分布曲线陡峭；日落前后近地面气溶胶浓度迅速增长，均值为1450cm，垂直分布曲线平缓。气溶胶粒子谱多为单峰分布，峰值为0．11μm；12：。0谱最宽，日落后到日出前谱变窄，且随高度增加谱变窄；当天气不稳定、湿度大时谱变宽。

Measurements of atmospheric aerosols over the mid-western region in North China Plain were conducted using the modified Particle Measuring Systems on board the Cheyenne aircraft by the Weather Modification Office of Hebei Province. The vertical and horizontal distributions of aerosol number concen- tration （ANC） and size distribution under different weather conditions were studied using the observations from 19 flights in October 2010. The results show that the aerosols over the study region mainly come from the underlying surface which are controlled by the inversion layer and wind shear in the boundary lay- er. The observed surface ANC is 1 000~3 000 em a and the average diameter is 0. 18--0.20 μm. It is found that the ANC is lower over Shijiazhuang area than that of Xingtai aera, The ANC over Boxiang county is close to that of Shijiazhuang area. The ANC （1 075--4 019 cm-3） is the highest near the surface and decreased exponentially with height. Under the high clouds, ANC shows the linear distribution in the lower part and negative exponential distribution in the higher part of the boundary layer. ANC is related to weather conditions and it has the minimum value after light rain （102 cm-3 near the surface） and could reach 10a cm-3 under the sunny days or days with dense clouds and high clouds. The diurnal variation of surface ANC shows a maximum value in the morning （1 799 cm-a） and a minimum value at noon （706 era-a）, and a rapid increase in the afternoon. The average ANC is 994 cm-3 in the evening. The vertical distribution of ANC is steep at noon and flat in the morning and afternoon with a collapse below the bound- ary layer. Accumulation of aerosols near the surface could easily lead to air pollution. Diurnal variation of temperature inversion layer also affects the diurnal variation of aerosol vertical distribution. The aerosol size distribution shows a single peak at 0. 11 μm in most of the time and had the widest spectrum at noon. It narrowed down with height and broadened under unstable and high humidity weather conditions.