基于航测数据的河北中南部雾霾天气气溶胶及云凝结核研究

Aircraft Study of Aerosol and CCN Under Foggy/Hazy Weather Condition in Autumn over the Central and Southern Hebei

2009年秋季利用夏延飞机观测平台对河北中南部雾霾天气条件下的气溶胶及云凝结核CCN进行观测,得到气溶胶、CCN数浓度及尺度的垂直廓线及粒子谱等特征,研究雾霾天大气气溶胶的分布、来源特征以及气溶胶与云凝结核的转化关系。研究发现:霾天气条件下边界层附近的气溶胶垂直分布特征有很大不同。边界层以上气溶胶浓度随高度递减,数浓度量级约101~102个·cm^(-3);边界层附近和近地面气溶胶浓度有峰值出现,近地面数浓度量级达103个·cm^(-3)。气溶胶粒子平均直径范围为0.16~0.18μm。600 m、1 000~2 000 m之间的气溶胶平均粒子谱大体呈单峰分布;3 000~4 000 m、6 000~6 900 m之间的粒子谱呈双峰分布。受气溶胶来源及特性差异的影响,在0.3%过饱和度下,3 000 m以下的气溶胶活化为CCN的比例不到20%,3 000 m以上活化比例高达50%。Hysplit后向轨迹模拟的气团移动轨迹显示,6 000 m以上的大气高层受我国西北地区远距离输送作用影响,沙尘粒子吸湿活化为CCN。低层气溶胶主要受下垫面及近地面污染排放影响,气溶胶尺度相对较小,气溶胶转化为CCN的比例低于高层。CCN浓度随过饱和度的增加呈增大趋势。利用多项式对气溶胶浓度和CCN浓度进行拟合,拟合结果与实测谱吻合较好。

Aircraft measurements of atmospheric aerosol and cloud condensation nuclei （CCN） over the central and southern Hebei were carried out in autumn of 2009. The spatial distribution, source of aerosol and its relationship with CCN under foggy/hazy weather condition were analyzed. The results show that there was a significant difference in the vertical distribution of aerosol number concentration near the boundary layer. The aerosol number concentration decreased with height above boundary layer, it was about in 101 - 102 order of magnitude. There was a peak value of aerosol number concentration near the boundary layer and near - surface. The aerosol number concentration was in 103 order of magnitude near surface. The range of aerosol mean diameters was between 0.16 and 0. 18 μm. The aerosol size distribution showed an unimodal mode on 600 m, between 1 000 and 2 000 m, while from 3 000 to 4 000 m, 6 000 to 6 900 m it showed a bimodal （multimodal） mode. Due to the different sources of aerosol, the conversion ratio of aerosol to CCN was less than 20% below 3 000 m, and it reached 50% above the level at 0.3% super -saturation. The air mass back trajectories showed that the aerosols at higher levels above 6 000 m were affected by the long distance transport from the northwest, the dust might be transformed to CCN. The aerosols at lower levels were affected by local pollution, therefore the particle size was smaller and the conversion ratio of aerosol to CCN was lower than that at higher level. The CCN concentration increased with super - saturation. The aerosol and CCN concentrations at different height were fitted with polynomial function. The relationship between aerosol and CCN concentration was established.