Mercury Deposition in Snow near an Industrial Emission Source in the Western U.S. and Comparison to ISC3 Model Predictions

摘要: Mercury (total and methyl) was evaluated in snow samples collected near a major mercury emission source on the Idaho National Engineering Environmental Laboratory (INEEL) insoutheastern 160 km downwind Teton Range westernWyoming. The sampling done to assess near-field (<12 km)deposition rates around source, compare them those measured relatively remote, pristine location, andto use measurements develop improved, site-specific modelinput parameters for precipitation scavenging coefficient thefraction of Hg emissions deposited locally. Measured waterconcentrations (ng L-1) were converted deposition (ugm-2) using sample location water equivalent. Thedeposition then compared that predicted ISC3 airdispersion/deposition model which run with range ofparticle vapor input values. Acceptedmodel statistical performance measures (fractional bias andnormalized mean square error) calculated differentmodeling runs, best selected. concentrations close (average = 5.3 ngL-1) about twice Range(average 2.7 ng within expected rangeof values remote background areas. For most samplinglocations, factor two theobserved deposition. modeling obtainedusing value 0.25 μm diameterparticulate assumption all isreactive Hg(II) subject local A 0.1 particle provided conservative overprediction thedata, while resulted highly variable predictions. Partitioning fraction elemental Hg(0) (a U.S. EPA default combustion facility risk assessments) would have underpredicted observed fallout.