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Ranges of years in the chart represent 3-year averages. For example, 1989-1991 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 for the 3-year period. Only sites meeting completeness criteria for at least two of the three years of the averaging period were included.
Wet deposition for each year was calculated as the product of the concentration grid from NADP/NTN and the grided precipitation amount estimated from the PRISM model.
Total deposition was calculated as the sum of the wet deposition measured by NADP/NTN and modeled dry deposition from CASTNET measurements. These estimates do not include deposition from ammonia gas or organic nitrogen.
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