Maps

	Ambient Concentrations
	Ambient Concentrations for Eastern U.S.
	Concentrations of Wet Deposition
	Wet Deposition

Color gradient maps were generated in ArcInfo GIS software using an inverse distance weighting (IDW) interpolation technique. Using IDW, the surface is most influenced by the nearest point values and less so by more distant points. Sites within 400 km of each grid point were used in the computation. White areas on the maps are areas where monitoring sites are absent and no information is available.

Ranges of years in the chart represent 3-year averages. For example, 89-91 is the average concentration of 1989,1990 and 1991, as calculated from gridded output for each of the years. The three annual grids from the 3-year period were averaged to derive the mean concentration of the 3-year period. Only sites meeting completeness criteria for at least two of the three years of the averaging period were included.

Maps

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