It pointed out that the air quality in urban area is meanly determined bynatural ventilation but the dry settling and rainout play a very important rolein the scrubbing processes.

• 要改善城市大气环境，除限制排放及高烟囱集中排放外，还可在低源群四周设置防护林带及人工雨装置来清除低源烟云，并给出了林带及人工雨带宽度的计算公式。