A SPATIAL MODEL OF ATMOSPHERIC DEPOSITION FOR THE NORTHEASTERN UNITED-STATES

Spatial patterns of atmospheric deposition across the northeastern Uni ted States were evaluated and summarized in a simple model as a functi on of elevation and geographic position within the region. For wet dep osition, 3-11 yr of annual concentration data for the major ions in pr ecipitation were obtained from the National Atmospheric Deposition Pro gram/National Trends Network (NADP/NTN) for 26 sites within the region . Concentration trends were evaluated by regression of annual mean con centrations against latitude and longitude. For nitrate, sulfate, and ammonium concentrations, a more than twofold linear decrease occurs fr om western New York and Pennsylvania to eastern Maine. These trends we re combined with regional and elevational trends of precipitation amou nt, obtained from 30-yr records of annual precipitation at > 300 weath er stations, to provide long-term patterns of wet deposition. Regional trends of dry deposition of N and S compounds were determined using 2 -3 yr of particle and gas concentration data collected by the National Dry Deposition Network (NDDN) and several other sources, in combinati on with estimates of deposition velocities. Contrary to wet deposition trends, the dominant air concentration trends were steep decreases fr om south to north, creating regional decreases in total deposition (we t + dry) from the southwest to the northeast. This contrast between we t 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 wes t and dry deposited materials primarily from urban areas along the sou thern edge of the region. The equations generated describing spatial p atterns of wet and dry deposition within the region were entered into a geographic information system (GIS) containing a digital elevation m odel (DEM) in order to develop spatially explicit predictions of atmos pheric deposition for the region.