Isotopic fractionation of gaseous mercury in a large industrial city: Spatio-temporal variations and source apportionment

The source-receptor relationship of atmospheric mercury is a critical environmental concern. However, comprehensive evaluations of mercury pollution based on spatially resolved and time-averaged data have not yet been conducted in Korea. In this study, the spatio-temporal variations of total gaseous mercury (TGM) and mercury isotopes were examined using passive air samplers at 30 sites in Ulsan over one year. TGM concentrations ranged from 2.26 ng/m3 to 68.5 ng/m3 with a mean of 6.89 ng/m3. Mean TGM concentrations by season were the highest in summer (9.28 ng/m3), followed by spring (7.31 ng/m3), winter (6.57 ng/m3), and fall (4.41 ng/m3). The highest concentration occurred in a non-ferrous industrial complex (21.9 ng/m3). Seasonal winds significantly influenced gaseous mercury dispersion to surrounding areas. The mean contributions of anthropogenic emissions, surface evasion, and background effects to TGM levels were 73 %, 2 %, and 25 % during summer and 49 %, 12 %, and 39 % during winter, respectively. The results indicate that anthropogenic emissions are the major source of gaseous mercury in the coastal city of Ulsan, particularly during summer when southeasterly winds are prevalent. This study is the first to present spatial and seasonal distribution maps of source contributions to TGM concentrations using mercury isotope analysis and a ternary mixing model.