During the period 2-4 February 1987 one of the most severe episodes of polluted air, which has ever been registered in Sweden, occured over southern Sweden.The sulfur dioxide concentrations reached at that time daily mean values around 300 μg m-3 in background as well as in urban areas. The sulfur dioxide concentrations were in urban areas along the Swedish west coast 10- 20 times higher and in background areas 40-50 times higher than the normal mean levels of sulfur dioxide at the corresponding places. Also higher concentrations of nitrogen oxides and soot occured.The meteorological transport calculations show that very large sulfur emissions in Central Europe had contaminated the air that reached southern Sweden during the period 2-4 February. The emissions of sulfur dioxide and soot in Central Europe were extremely large due to the very cold weather. During the period very stable stratification occured in the lower parts of the atmosphere, which caused very limited turbulent dispersion and dilution of the air pollutants. The high concentrations of sulfur dioxide and soot, which occured over southern Sweden , were to a larger part (about 90% or more) caused by the long range transport of air pollutants.