The purpose of this investigation was to estimate the yearly ambient concentration of SO2 and SO4 wet deposition from 1880 to 1980 for the greater New York City area. This information was used to reconstruct ambient concentrations at two New York Veterans Administration cemeteries, Cypress Hills and Long Island, for studying marble deterioration. This study which involved a determination of marble loss rate as a function of SO2 concentrations is the subject of another report. The methodology for developing the retrospective model to estimate yearly ambient concentrations since the turn of the century for the greater New York City area is presented in this report. The retrospective estimation of sulfur concentration and deposition required estimation of both local and regional emission trends since the turn of the century, along with suitable choice of a local and a regional dispersion model to relate emissions to ambient concentrations and deposition. The retrospective estimates are compared to observed SO2 concentrations. It needs no elaboration that the estimation of local and regional emissions pertinent to a given receptor, the quantification of the local and regional contributions to SO2 and to the wet deposition, and reconciliation with existing observations is a formidable task. Lacking data for the historical trends, many of the assumptions are based on 'best available science', and they should be revised with the availability of new knowledge.