Characteristics of Atmospheric Wet Deposition of Total Mercury in Seoul, Korea

Abstract

Precipitation samples for total mercury (TM) were collected with a modified MIC-B sampler concurrent with atmospheric gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) concentrations on the roof of Graduate School of Public Health building in Seoul, Korea from January 2006 to December 2009. These samples were used to determine the seasonal variations in TM wet deposition, to determine the contribution of GOM and PBM scavenging to mercury wet deposition, and to identify source areas contributing to the high TM wet deposition using a Lagrangian particle dispersion model (LPDM). The volume weighted mean (VWM) TM concentrations in 2006, 2007, 2008, and 2009 were 10.1 ± 17.0 ng L-1, 16.3 ± 16.5 ng L-1, 14.3 ± 11.9 ng L-1, and 10.2 ± 14.8 ng L-1, respectively and the TM wet deposition flux in 2006, 2007, 2008, and 2009 were 16.8 ug m-2, 20.2 ug m-2, 18.5 ug m-2 and 16.4 ug m-2, respectively. During the sampling period, the VWM TM concentration was highest in winter, followed by spring, fall, and summer while the wet deposition flux was highest in summer, followed by spring, fall, and winter.

Nonparametric Mann-Whitney test revealed that there were statistical differences in VWM TM concentration between winter and other seasons (p<0.01) and there were statistical differences in wet deposition flux between summer and other seasons (p<0.01) except winter (p=0.09). The high VWM TM concentration in winter was associated with the combined effect of the low rainfall depth and high speciated mercury (GOM and PBM) concentrations. In addition, the high VWM TM concentration in spring was due to the yellow sand events suggesting that GOM and PBM present in the rain were long-range transported from China during this period. Yellow sand events occurred immediately prior to wet deposition events in 2006 and in 2007. During those periods GOM and PBM concentrations were elevated resulting in high VWM TM concentrations. The high TM wet deposition flux in summer (53% of total TM wet deposition flux) was primarily due to the high precipitation rate in summer (77% of total rainfall depth). Multiple linear regression showed that scavenging coefficient (SC) for GOM was much higher than SC for PBM suggesting that GOM was more effectively scavenged by wet deposition than PBM (SCGOM = 715 and SCPBM = 407). Joint-probability LPDM (JP-LPDM) indicated that the main sources of TM wet deposition were Guizhou, Guangdong, Liaoning, Hunan, Shaanxi, Nei Mongol and Gobi Desert. This suggests that both anthropogenic sources such as industrial areas and natural source areas such as deserts contributed to the high TM concentration in Seoul, Korea.