During the spring of 2001, a number of severe dust storms occurred in the northwest area of China. The dust storm event on 7-9 April 2001 was one of the most intensive and widespread in time and space. It caused serious air quality problems over the broad area covering several provinces (such as southern Xinjiang, Qinghai, Gansu and Ningxia) downwind from Xinjiang Taklamakan Desert and the Inner Mongolia source areas. It also impacted the air quality farther downwind in East China, Japan and Korea. The dust was  even transported across the Pacific to the continent of North America as revealed by satellite observations, in-situ measurements and modeling. To study the formation of this dust storm and its air quality impact, operational synoptic data, satellite observations, and surface observations of meteorological variables and data are collected and analyzed. Numerical simulations of this event are performed by using the Navy's COAMPS with its newest versions of aerosol model and soil-vegetation model. The preliminary results indicate that a mesolow developed ahead of the synoptic-scale cold front prior to and during the time when dust storm broke out. This mesoscale system seems to be responsible for the formation of the dust storm. Detailed analyses will be performed and presented at the conference.