高 原 气 象 41 卷 1588 -3 图5 2014-2018年污染季不同环流型下PM 浓度的分布(单位:μg∙m ) 2. 5 Fig. 5 Spatial distributions of PM 2. 5 concentration under different synoptic circulation types during the pollution seasons from 2014 to 2018. Unit:μg∙m -3