华北地区气溶胶数浓度和尺度分布的航测研究 ——以石家庄为例

2009年秋季利用河北省人工影响天气办公室机载气溶胶粒子探头(PCASP-100X)和前向散射滴谱探头(FSSP-100-ER)在石家庄市上空进行了多次气溶胶观测.选取2009年9~10月间的7架次雾天、1架次小雨天及1架次密卷云天观测资料,重点研究雾天气溶胶粒子数浓度和直径的垂直、水平分布特征及粒子谱分布,并与密卷云天和小雨天的探测资料进行对比分析.结果表明:石家庄地区气溶胶粒子数浓度较高,近地面最大值达11910个/cm3.气溶胶粒子数浓度主要受天气条件影响,逆温层是影响粒子垂直输送的主要因素,在逆温层下粒子累积形成粒子数浓度的高值区,逆温层以上气溶胶粒子数浓度迅速减少,雾天和密卷云天粒子数浓度随高度多呈负指数分布;雾天多伴有逆温层和较大空气湿度,有利于气溶胶粒子累积,数浓度一般可达104个/cm3以上,容易形成低能见度污染天气;气溶胶粒子数浓度在无降水日有累积效应,降雨对气溶胶粒子有明显清除作用;粒子数浓度和粒子直径在水平方向上呈不均匀分布,随着高度增加粒子数浓度和直径的水平绝对偏差减小,相对偏差往往增大;不同天气下尺度谱型类似,多呈单峰分布,在0.11μm左右处出现峰值,但在雾天、密卷云天、小雨天气下的气溶胶粒子峰值依次变小,并且随高度增加,尺度谱峰值数密度值降低,谱变窄.

Aerosol distribution in North China Plain under different weather conditions

Aerosol measurements were conducted over Shijiazhuang area, Northern China, during the autumn of 2009, using the airborne Particle Measuring Systems (PCASP-100X, PMI Co. Ltd, USA) and forward scattering spectrum probe (FSSP-100-ER, PMI Co. Ltd, USA) of Weather Modification Office of Hebei Province. Measurements obtained in September and October in 2009 from seven flights in foggy days, one flight under rainy weather, and another flight under cloudy condition were chosen in this study to investigate the vertical and horizontal distributions of the concentration and mean diameter, as well as the size distribution of aerosol particles. Aerosol pollution over Shijiazhuang was quite heavy as compared to cleaner background regions, with the maximum particle concentration reaching 11910cm-3 near the ground. It was also shown that the concentration of aerosol particles was mainly affected by weather conditions, and inversion layer was the main factor that controls the vertical distribution of aerosol particles. High concentration of aerosol particles was measured below an inversion layer, but it decreased rapidly above the inversion layer. Foggy days were usually associated with inversion layer and larger humidity, and was favorable of aerosol accumulation, therefore, maximum concentration of 104cm-3 was measured under foggy weather, aerosol particles were accumulating with the days of non-precipitation before it reached the maximum and precipitation had a significant effect on aerosol removal. The results also indicated that the distributions of the concentration and size of aerosol particles were non-uniform in horizontal, and their absolute variations decreased with height and relative variations increase with height. Aerosol size distribution under the three weather conditions were similar with a single peak at about 0.11μm, but the peak values of the aerosol number concentration decreased under the condition of foggy, Ci dens, and light rain conditions. With the increase in altitude, the peak values of the particle size distribution was becoming smaller, and the spectrum was also getting narrower.