Variation and Transportation Characteristics of SO2 in Winter

Taking the advantage of the project “The study of the transportation and transformation of air pollutants in Beijing and its surrounding areas and the objective of air quality in Beijing”, which is of the program of air quality assurance for Beijing 2008 Olympic Games, the continuous observations of SO2 concentrations were made with two advanced DOAS（Differencial Optical Absorption Spectroscopy） instruments and a gas analyzer in the premises of the Institute of Atmospheric Physics, Xianghe Atmospheric Integrated Observatory, and Xinglong Atmospheric Composition Background of Chinese Academy of Sciences during 15〖CD*2〗27 January 2007. Meanwhile, the meteorological observations were conventionally made with the 32 m tower equipped with a set of meteorological instruments, and the meteorological parameter profiles were obtained by tethered balloons. Based on the measurements in these sites, the aspects of processes, variations, transportations, emissions of the SO2 pollution in Beijing and its surrounding areas, and its relationships with weather processes or conditions, are analyzed. The results are as follows: 1) The daily variations in the three sites are obvious and the tendency is the same. This implies that for Beijing and its surrounding areas, it is usually under the control of the same weather system. Therefore, SO2 pollution is regional. 2) The SO2 concentration has an obvious diurnal variation with the highest concentration at night and lowest at 1500 LST. 3) There is a close relationship between the variation of SO2 concentration and atmospheric stability, wind speed and wind direction. The smaller the wind speed and atmosphere stability is, the higher SO2 concentration is. Higher SO2 concentration is from southwest direction. 4) Simulations of the backward trajectory model HYSPLIT and OMI SO2 retrievals indicate that long path transportation of SO2 from surrounding areas can not be neglected.