Wet and dry deposition fluxes of mercury in Japan

Abstract

Wet and dry deposition fluxes of mercury were measured concurrently from December 2002 to November 2003 at 10 sites in Japan (nine sites for dry deposition measurements). Precipitation and dry deposition (gases and particles) were collected every half-month using an automatic wet and dry deposition sampler. This sampler is composed of a precipitation sampler and a water surface sampler for dry deposition. The results showed that wet deposition fluxes of mercury increase generally during summer when the precipitation amount increases. In contrast, the seasonal variations of the dry deposition fluxes were very small compared to those of the wet deposition fluxes. It was found that wet deposition plays a dominant role in mercury deposition in Japan, contributing fluxes ranging from 0.99 to 2.2 times (1.6 times on average at nine sites) those of the dry deposition fluxes. There was a high correlation between the annual wet deposition flux of mercury and annual precipitation amount (r2=0.73, P<0.01). Thus, about 70% of the variance of mercury wet deposition in Japan is explained by precipitation amount. This is probably because mercury wet deposition is dominated by the scavenging of reactive gaseous mercury (RGM) by precipitation via oxidation of gaseous elemental mercury (Hg0) in the gas and aqueous phases. In addition, a similar relationship between the annual wet deposition flux and precipitation amount (r2=0.55, P<0.001) was observed at the Mercury Deposition Network (MDN) sites in North America, suggesting that about 55% of the variance of mercury wet deposition is due to precipitation amount.