Modeling study of reactive gaseous mercury in the urban air

Chemical speciation and concentrations of reactive gaseous mercury (RGM) in the urban atmospheric boundary layer (ABL) have been modeled using a photochemical box model. Measurements for gaseous elemental mercury (GEM) and the relevant trace gases were carried out in Seoul (37.6°N, 127°E), Korea, during a one-year period from March 2001 to February 2002. A moderately strong inverse correlation between GEM (Hg(0)) and ozone was observed in the spring. In addition, it was also observed that there were distinct GEM concentration differences between day and night, especially in the winter. Model simulations suggested that the most dominant sink of elemental mercury (Hg(0)) was the reaction with O3, which in turn contributed significantly to the formation of mercury oxide (HgO). The dominant RGM species in the urban ABL are likely to be HgO and Hg(HO)2. Seasonally averaged concentrations of HgO and Hg(HO)2 are estimated to range from 0.5×104 to 1.1×104 and 0.2×104 to 3.5×104 molecules cm−3, respectively. According to our model simulations, most RGM species are expected to exhibit relatively enhanced concentrations during the daytime compared to the nighttime.