中文摘要：

随着经济规模迅速扩大和城市化进程加快,大气气溶胶污染日趋严重,由细粒子气溶胶造成的能见度恶化事件越来越多,这些人类活动排放的污染物,可形成灰霾天气致使能见度下降.2010年3月17—23日,在珠三角地区发生了一次典型灰霾天气过程,同期20日左右,中亚、蒙古国与我国北方发生了当年沙尘天气影响范围最广的一次强沙尘暴过程,冷空气前锋22日凌晨到达穗港地区,但穗港两地空气质量发生了相反的变化,香港空气质量急剧恶化,气溶胶浓度超过700μg·m-3,而珠三角腹地的广州、佛山、东莞的能见度和空气质量明显好转,出现了穗港晴沙两重天的奇观,亦引发了关于这次过程定性的争议.本文从天气分析、流场分析、遥感分析和气溶胶物理化学特征分析,探讨了这次过程的成因,结论是香港地区从东到西受到了源于浮尘的重度灰霾天气影响,能见度和空气质量急剧恶化,而珠三角腹地受冷空气影响,清除了持续6d的灰霾天气,能见度和空气质量明显好转.

英文摘要：

With the rapid expansion of economy and urbanization,atmospheric particulate matter （PM） pollution becomes more and more serious.Low visibility episodes happen more frequently due to the increasing concentration of fine PM.We report here an analysis of a typical haze episode observed in the Pearl River Delta （PRD） region during 17—23 March 2010.In this period,the most extensive sand and dust storm of 2010 occurred in Central Asia,Mongolia and northern China.At the same time,a cold front arrived at the Hong Kong and Guangzhou area in the early morning of 22 March 2010.Rapid deterioration of air quality was observed in Hong Kong,with PM concentration exceeding 700 μg·m-3.In contrast,air quality and visibility of the inland part of the PRD,including Guangzhou,Foshan and Dongguan,showed significant improvement during this period.This sharp contrast has triggered debate on the atmospheric processes affecting this region.In this paper,we present an investigation of the cause for the observed contrast in air quality by examining weather conditions,wind flow field,remote sensing data,and physical and chemical characteristics of PM.We conclude that the extreme degradation in air quality and visibility experienced in Hong Kong was caused by the dust event while the clear sky in the PRD inland areas was a result of the cold front sweeping away previously accumulated pollution.