Haze, which is composed of a wide range of aerosol particles, is one of the most hazardous weather conditions because of its adverse impact on health and its deleterious effect on visibility, leading to loss of maritime transportation. Satellite, ground-based sunphotometer and particulate matter (PM) concentration data were analysed to evaluate the causes of two severe haze episodes observed during 28-31 March and 3-6 June 2007 over the Yellow Sea. The first episode was clearly affected by the

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... ong-range transport of dust from southeastern Mongolia to eastern Inner Mongolia, covering the Onqin Daga and Horqin sandy land areas, which are important sources for the sand and dust storms (SDS) that occur frequently during the spring in East Asia. A backward trajectory analysis confirmed the transport of air mass from southeastern Mongolia. A very high aerosol optical depth (AOD) (. 2.0) and a high backscatter coefficient (about 5 Â 10 -2 km sr -1 ) of dust were observed by Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), respectively, during the first haze episode. A sudden increase in PM 10 (particles 10 mm) concentration (maximum value 225 mg m -3 ) was observed during the haze period. A higher AOD was observed over the Yellow Sea on 6 June 2007 during the second haze event compared to the AOD observed during the first haze episode, which occurred during 4-6 June 2007. A few hotspots were detected by MODIS during the second haze episode. It was concluded that the second haze episode was probably dominated by smoke from open burning areas of crop residue in East China, when a rapid increase in PM 10 concentration up to 192 mg m -3 was observed.