Excerpt from Mercury Study Report to Congress Volume Iii: Fate and Transport of Mercury in the Environment

This chapter summarizes the results of the atmospheric fate and transport modeling of mercury using the long-range and local models. The general mass balance of elemental mercury gas, divalent mercury gas, and particle-bound mercury from the RELMAP simulation results using the assumed emission speciation profiles are shown in Table 5-1. The mass-balance accounting for the simulation using the meteorological data from the year 1989 shows a total of 141.8 metric tons of mercury emitted to the atmosphere from anthropogenic sources. This simulated emission total differs slightly from the national totals indicated in Volume II since the states of Alaska and Hawaii are not within the model domain. The RELMAP simulation indicates that 47.6 metric tons of anthropogenic mercury emissions are deposited within the model domain and 0.4 metric tons remain in the air within the model domain at the end of the simulation. The remainder, about 93.8 metric tons, is transported outside the model domain and probably diffuses into the global atmospheric reservoir. The simulation also shows 32.0 metric tons of mercury is deposited within the model domain from the global atmospheric reservoir, suggesting that about three times as much mercury is being added to the global reservoir as is being deposited from it. The total amount of mercury deposited in the model domain annually from U.S. anthropogenic emissions and from the global background concentration is estimated to be 79.6 metric tons, or slightly more than one-half of the mass of all atmospheric emissions from anthropogenic sources in the lower 48 United States.