A new method for evaluating dry deposition of mercury using a water surface sampler

Abstract
A new method of using a circular water surface sampler was devoloped to evaluate the dry deposition fluxes and deposition velocity (= deposition flux/atmospheric concentration) of particulate mercuty, Hg(p) and gaseous divalent mecury, Hg(II) individually. Observations were conducted at a study site located in the Tokyo metropolitan area. The results showed that the water surface sampler could be used to measure the dry deposition fluxes of mercury and other trace metals (Cd, Cu, Mn, Pb and Zn). The dry depostion velocity for trace metals other tann mercury, which exist entirely in particulate form, increased linearly with increasing median diameter in the size distribution. Using this regression equation, the dry deposition velocity for Hg(p) can be estimated from its median diameter, which allows us to calculate the dry depostion flux for Hg(p). On the other hand, the dry depostion flux for Hg(II) can be obtained from the difference between the depostion flux measured using the water surface sampler and the estimated depostion flux for Hg(p). This makes it possible to estiate the dry depostion velocity for Hg(II) bu dividing the deposition flux by the atmospheric concentration.