Regional reductions in NOx emissions, principally from utility plants, are a focus for reducing urban and regional zone (O3) concentrations in the United States (U.S. EPA, 1998). In current regulatory analyses of benefits and costs of proposed NOx emissions reductions for O3 control, the change in fine particulate concentrations is also taken into account, because of major health concerns regarding fine particulates. Fine particulates are defined as particles which a diameter less than 2.5 microns. Regional oxidant production is generally NOx-limited. Therefore, significant reductions of NOx emissions and thereby NOx concentrations would be expected to change the regional oxidizing capacity of the atmosphere. From the one-atmosphere perspective, it is then natural to ask the question whether proposed NOx reductions will have any feedback on other pollutants. Fine particulate sulfate, henceforth sulfate, is a potential candidate because its production is associated with three different oxidants; hydroxyl radicals (OH), hydrogen peroxide (H202), and ozone (O3). In this paper the authors examine the feedback of NOx emission reductions on the production of sulfate.