The exchange of gaseous mercury across soil–air interface in a residential area of Seoul, Korea

Abstract

The exchange processes of elemental mercury across air–surface boundary were examined in terms of relationship between emission from and dry deposition to soil surfaces in a residential area of Seoul, Korea during the fall season of 1997. To measure Hg concentration gradients developed across two heights of 20 and 200 cm over soil surfaces, we conducted continuous analyses of Hg concentrations at hourly intervals over the whole study periods. From these measurements, we found that Hg concentrations in the lower and upper levels varied in the range 3.15–14.38 (5.30±1.88: N=236) and 2.07–15.10 ng m -3 (4.06±1.69: N=236), respectively. When divided separately into emission and dry deposition, our data showed that emission of Hg was overwhelmingly dominant in frequency (up to 98%) over dry deposition. The gradients for emission and deposition events derived as concentration differences between 20 and 200 cm were 1.29±0.86 ( N=231) and −1.0±1.27 ng m -3 ( N=5), respectively. In fact, the concentration and gradient data from our study site were even larger than what had previously been reported from highly contaminated soil environs of Tennessee, USA by Lindberg et al. The observations of notably high concentrations in both levels and development of strong gradients suggest that our study site be affected by the pollution sources of certain kinds. To provide some insights into the processes governing the Hg exchange processes in the selected study area, we have conducted correlation analyses between Hg data and the other concurrently determined meteorological plus chemical data. Although both Hg concentrations (of two levels) and the gradient data similarly exhibited the existence of strong correlations with most meteorological parameters, it was not the case with major pollutant components. It was also noticed that the Hg concentrations of the lower level were exhibiting systematically strong correlations with most parameters than those of upper level. To estimate Hg fluxes of our study site, we attempted to compute its fluxes indirectly using our gradient data and the K values predicted from the results of the previous studies. According to this rough estimation, emissions of Hg were generally occurring at 100±80 ng m -2 h -1 ( N=231), while depositions were on the similar magnitude of −90±130 ng m -2 h -1 ( N=5). Our findings of emission dominancy and of large gradient and flux development in the residential area of Korea suggest that airborne transport of mercury be a significant process, at least in some residential areas of Korea.