兰州城区TSP高浓度污染与自然降尘的关系

Relationship of Severe TSP Pollution and Natural Dustfall in Lanzhou City

从宁夏到甘肃中部有一个自北向南的少雨“干舌”,在垂直速度场上形成一个从河西东部向南伸下来的下沉运动区,冬季下沉运动区大而强烈,有利于空气中的沙尘下沉堆积。经分析,兰州城区自然降尘量占年降尘量的54%。随着沙尘暴、扬沙和浮尘天气的出现,自然降尘量由1月份的32%增大到5月份的60%;按春、夏、秋、冬四季划分,城区TSP浓度中自然降尘量各占58%、33%、28%和32%。全年中11月城郊浓度差值最大0.59mg.m-3,其主要原因是11月刚进入采暖期,除原有工业源外,又增加了采暖锅炉和生活小炉灶,TSP排放量增大,加之该月风速最小、天气过程少,是兰州市出现严重污染的主要原因。

There is a ＇dry tongue＇ （less rainfall） in north-south orientation between Ningxia Hui Autonomous region and middle part of Gansu province, forming a downwards moving region over the vertical velocity field from east of Hexi to south. The downwards moving region is intense and great in winter, which makes for air dustfall depositing. The result showed that the natural dustfall accounted for 54% of the total dust amount yearly. The natural dustfall ratio of different months are different due to sandstorm, blowing dust, and floating dust weather, such as the natural dustfall ratio increased from 32% of Jan to 60% of May. If differentiated by season, the natural dustfall accounted for 58% in spring, 33% in summer, 28% in autumn and 32 % in winter in TSP concentration. The TSP concentration difference between city and suburb is the biggest in Nov, because all the heating equipment begin opening, and the wind velocity and the precipitation are very little, so the severe pollution weather come in this period generally.