High concentrations of sulfur dioxide (SO2) are commonly observed during the cool season in the vicinity of a 2.5 GW coal burning power plant located in the Mae Moh Valley of northern Thailand. The power plant is the source for nearly all of the observed SO2 since there are no other major industrial activities in this region. These high pollution fumigation events occur almost on a daily basis, usually lasting for several hours between late morning and early afternoon. One-hour average SO2 concentrations commonly exceed 1,000 micrograms/cu m. As a result, an increase in the number of respiratory type health complaints have been observed by local clinics during this time of the year. Meteorological data were acquired from a variety of observing platforms during an intensive field study from December 1993 to February 1994. The measurements included horizontal and vertical wind velocity, air temperature, relative humidity, and solar radiation. In addition, turbulent flux measurements were acquired by a sonic anemometer. SO2 measurements were made at seven monitoring sites scattered throughout the valley. These data were used to examine the atmospheric processes which are responsible for these high pollution fumigation events.