中文摘要：

利用2000年3月-2008年2月中分辨率成像光谱仪（MODIS）的卫星资料，分析了京津冀平原地区大气气溶胶光学厚度（AOD）和气溶胶细粒子组分比率（FMF）的时空分布特征．结果表明：通过AOD与FMF的组合特征可判别气溶胶季节变化特征．冬、春季以粗粒子为主，但冬季AOD偏小，而在春季急剧增大；夏、秋季均以细粒子为主，但夏季AOD达到最大，秋季较小．大气环流和气流后向轨迹分析表明，冬季到达北京的气流以西北冷空气为主，西北路径的气流轨迹占冬季气流轨迹总数的67％；春季主要受偏西、西北及偏北气流影响，这3类对沙尘天气有贡献的气流轨迹占春季气流轨迹总数比例之和达到60％；夏季主要以偏南气流和局地环流占优，这2类气流轨迹分别占夏季气流轨迹总数的52％和34％；秋季气流轨迹与春季的相似，但途经沙源的气流传输速度较春季慢．京津冀平原地区夏季AOD与云量（CF）呈正相关，AOD增加，特别是细粒子增加可能导致局地云量增多．

英文摘要：

Based on 8-year （March 2000-February 2008） MODIS satellite data, the spatial and temporal distributions of aerosol optical depth （AOD） and fraction of fine-mode aerosols （FMF） were examined over the Beijing-Tianjin-Hebei plain area. The combined characteristics of AOD and FMF can be used to distinguish different atmospheric aerosol types in different seasons. In winter, coarse-mode aerosol is the dominant component with the lowest AOD values. In spring, AOD increases rapidly and coarse-mode aerosol is the main component. In summer, fine-mode aerosol serves as the dominant component, resulting in the highest AOD values. In autumn, AOD is lower with fine-mode aerosol still as the main component. Through the relevant atmospheric flow field and back trajectory analyses, it is found that the airflow reaching Beijing mainly comes from the northwesterly cold airflow. The northwesterly air flow trajectories account for 67% of all trajectories. In spring, there are three main air flows from the west, northwest and north. The ratio of desert-related trajectories is 60% of the total. In summer, southerly airflow and local airflow are the two main trajectories with ratios of 52% and 34% respectively. The average airflow trajectories of autumn are similar to those of spring despite lower transportation speed of trajectories passing deserts. In addition, a positive correlation between AOD and cloud fraction （CF） is observed in summer, which suggests that cloudiness could increase with amount of aerosol, especially fine-mode aerosol.