A Spatial Model of Atmospheric Deposition For the Northeastern U.S.

CLIMCALC is a simple model of physical and chemical climate for the northeasten United States (New York and New England) that can be incorporated into a geographic information system (GIS) for integration with ecosystem models presented. The variables include average maximum and minimum daily temperature, precipitation, humidity, and solar radiation, all at a monthly time step, as well as annual wet and dry deposition of sulfur and nitrogen. Regressions on latitude, longitude, and elevation are fitted to regional data bases of these variables The equations are combined with a digital elevation model (DEM) of the region to generate GIS coverages of each variableresults are from a model of atmospheric deposition called CLIMCALC. Spatial patterns of atmospheric deposition across the northeastern United States were evaluated and summarized in a simple model as a function of elevation and geographic position within the region. For wet deposition, 3-11 yr of annual concentration data for the major ions in precipitation were obtained from the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) for 26 sites within the region. Concentration trends were evaluated by regression of annual mean concentrations against latitude and longitude. For nitrate, sulfate, and ammonium concentrations, a more than twofold linear decrease occurs from western New York and Pennsylvania to eastern Maine. These trends were combined with regional and elevational trends or precipitation amount, obtained from 30-yr records of annual precipitation at >300 weather stations, to provide long-term patterns of wet deposition. Regional trends of dry deposition of N and S compounds were determined using 2-3 yrs of particle and gas concentration data collected by the National Dry Deposition Network (NDDN) and several other sources, in combination with estimates of deposition velocities. Contrary to wet deposition trends, the dominant air concentration trends were steep decreases from south to north, creating regional decreases in total deposition (wet + dry) from the southwest to the northeast. This contrast between wet and dry deposition trends suggests that within the northeast the two deposition forms are received in different proportions from different source areas, wet deposited materials primarily from areas to the west and dry deposited materials primarily from urban areas along the southern edge of the region. The equations generated describing spatial patterns of wet and dry depositions within the region were entered into a geographic information system (GIS) containing a digital elevation model (DEM) in order to develop spatially explicit predictions of atmospheric deposition for the region.