This final rule is being issued as required by a consent decree governing the schedule for completion of this review of the air quality criteria and the secondary national ambient air quality standards (NAAQS) for oxides of nitrogen and oxides of sulfur. Based on its review, the EPA is retaining the current nitrogen dioxide (NO<INF>2</INF>) and sulfur dioxide (SO<INF>2</INF>) secondary standards to address the direct effects on vegetation of exposure to gaseous oxides of nitrogen and sulfur and, for reasons described in detail in this final preamble, is not adding new standards at this time to address effects associated with the deposition of oxides of nitrogen and sulfur on sensitive aquatic and terrestrial ecosystems. In addition, in this rule the EPA describes a field pilot program being developed to enhance our understanding of the degree of protectiveness that would likely be afforded by a multi-pollutant standard to address deposition-related acidification of sensitive aquatic ecosystems.