Mathematical modeling of the atmospheric fate and transport of mercury (Hg) was conducted using three nested domains covering global, continental and regional scales with horizontal resolutions of approximately 1000, 100 and 20 km, respectively. Comparisons of modeling results with wet deposition fluxes show a coefficient of determination (r(2)) of 0.45 for the continental simulation and 0.14 for the continental/regional simulation. The poor correlation obtained in the regional simulation results to a large extent from the fact that the model predicts an increasing gradient in Hg wet deposition from Minnesota to Pennsylvania, which is not observed in the monitoring network. The use of a finer spatial resolution (20 km) improves model performance in Minnesota and Wisconsin (upwind of major Hg emission sources) but degrades model performance in Pennsylvania (downwind of major Hg emission sources). We suggest the hypothesis that some key Hg chemical transformations are likely missing in current models of atmospheric Hg.