Estimation of nitrogen and sulfur dry deposition in the Greater Seoul Area

While deposition is a removal process of pollutants from the atmosphere, it is an intake process of such pollutants to the ground. Fifteen years ago, Seoul was notorious for serious pollution of sulfur dioxide and suspended particulate matter; now, it suffers from frequent high ozone occurrences. It is suggested that surface waters in the Greater Seoul Area, used as a source of drinking water, have been affected by severe air pollution. In this work, dry deposition amounts of nitrogen and sulfur species were estimated for three typical days in each season for the year of 1997. The CIT (California Institute of Technology) photochemical model incorporated with a gaseous oxidation reaction of SO2 was used. Emission data were prepared by scaling the data from the National Institute of Environmental Research, Korea. Meteorological data were prepared diagnostically by using observations from both the surface weather stations and densely populated automatic weather stations. The study revealed that nitrogen deposition was the highest in summer and sulfur deposition in winter. Most of nitrogen was deposited in the form of HNO3 and NO2 as a result of high deposition velocity of HNO3 and of high concentration of NO2. On the other hand, the contribution of sulfate to the total deposition of sulfur was minor, even considering the heterogeneous formation of sulfate estimated from the observations, mainly because of low deposition velocity. Approximately 55% of nitrogen and 30% of sulfur emitted in the study area were deposited to the ground in the dry form on an annual base.