We investigated the temporal and spatial distribution of SO2 measured at 14 air pollution monitoring sites in Ulsan, Korea. The levels of SO2 in Ulsan have continuously decreased since the 1990s, and a recent (2005-2009) annual average concentration of 8 ppb is lower than the national guideline of 20 ppb. However, Ulsan has higher levels of SO2 than any other mega-city in Korea. The average level of SO2 at industrial sites (13.7ppb) is 2.4 times higher than those at residential and commercial sites. According to the measurement data, meteorological condition, and former air dispersion modeling results, it was confirmed that SO2 emitted from the industrial complex was transported to the residential area by sea-land breeze and southeastern seasonal winds. For the improved air quality in Ulsan, the current environmental policy permitting the use of high-sulfur oil (<4%) should be carefully evaluated. The emission of greenhouse gases and hazardous air pollutants (HAPs) as well as SO2 from plants using the high-sulfur oil should be monitored. Furthermore, separated environmental policies for the industrial and residential areas are required for more effective pollution management.