When implemented, that rule will achieve significant, cost-effective summertime NOx emissions reductions in 22 states and the District of Columbia. Environmental Trends, Modeling and Continued Concerns for Natural Resources Environmental data are beginning to reflect improvements accompanying the downward emissions trend, but fundamental concerns regarding recovery persist. The nation's deposition monitoring networks have shown significant reductions in sulfate concentrations measured in both wet and dry forms. Results from an analysis of long-term surface water monitoring data have confirmed that acid sensitive lakes have experienced significant declines in sulfate concentrations in response to declining sulfate deposition. Surface water nitrate levels, however, have not shown significant upward or downward trends which is also consistent with trends in nitrate concentration levels in deposition.
High elevation lakes in the western U.S. are also vulnerable to sulfur and nitrogen loadings.
In 1995, the EPA sent to Congress its Acid Deposition Standard Feasibility Study. Recent evidence also points to atmospheric nitrogen deposition as a significant contributor to total nitrogen loading to coastal waters along the East and Gulf coasts and nutrient loading in large river basins. Recent analyses of estuaries along the East and Gulf coasts have estimated the nitrogen contribution from atmospheric sources to range from 10 to 45 percent. These conditions have important implications for the biological communities. Multiple Effects Associated with Sulfur Dioxide and Nitrogen Oxides Emission Reducing SO2 and NOx provides multiple environmental and human health benefits.