Relationship of Severe TSP Pollution and Natural Dustfall in Lanzhou City
兰州城区TSP高浓度污染与自然降尘的关系

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.