Abstract
In this study, the model response in terms of simulated mercury concentration and deposition to boundary condition (BC),
initial condition (IC), model grid resolution (12 km versus 36 km), and two alternative Hg(II) reduction mechanisms, was
investigated. The model response to the change of gaseous elemental mercury (GEM) concentration from 0 to 2 ngm3 in IC/BC
is found to be very linear (r240.99) based on the results of sensitivity simulations in July 2001. An increase of 1 ngm3 of GEM in
BC resulted in an increase of 0.81 ngm3 in the monthly average of total mercury concentration, and 1270 ngm2 in the monthly
total deposition. IC has similar but weaker effects compared to those of BC. An increase of 1 ngm3 of GEM in IC resulted in an
increase of 0.14 ngm3 in the monthly average of total mercury concentration, and 250 ngm2 in the monthly total deposition.
Varying reactive gaseous mercury (RGM) or particulate mercury (PHg) in BC/IC has much less significant impact. Simulation
results at different grid resolutions show good agreement (slope ¼ 0.950–1.026, r ¼ 0.816–0.973) in mercury concentration, dry
deposition, and total deposition. The agreement in wet deposition is somewhat weaker (slope ¼ 0.770–0.794, r ¼ 0.685–0.892) due
to the difference in emission dilution and simulated precipitation that subsequently change reaction rates in the aqueous phase.
Replacing the aqueous Hg(II)-HO2 reduction by either RGM reduction by CO (51018cm3 molecule1 s1) or photoreduction
of RGM (1105 s1) gives significantly better model agreement with the wet deposition measured by Mercury Deposition
Network (MDN). Possible ranges of the reduction rates are estimated based on model sensitivity results. The kinetic estimate
requires further verification by laboratory studies.