Without this, the role of NO X in the atmosphere and ecosystem cannot be completely and quantitatively understood. Currently, our knowledge of NO X releases from pollution sources is based on a vehicle emission inventory, which is believed to be comprehensive, and on emission inventories for stationary, area, and fugitive sources, which are comparatively incomplete. In some areas, however, data indicate that wet nitrate deposition has increased, while sulfate deposition has decreased. For example, NADP precipitation chemistry data, which track the fate and transport of pollutants from local and upwind sources, show transfers of air contaminants to sensitive Vermont aquatic and terrestrial ecosystems. Figure 2-1 shows nitrate and sulfate concentrations in rain and snow in Bennington, Vermont, from 1981 to 1995.
Nitrate concentrations appear to have increased, while sulfate concentrations have decreased.
This decline in sulfate deposition is believed to be a consequence of SO X reductions from power plants in the eastern United States, where further reductions are anticipated as Title IV of the U.S. CAA continues to be implemented. The increase in nitrate deposition is believed to be due to the lack of concurrent efforts to reduce NO X emissions from vehicles and power plants. X emission reductions can be expected in the next few years as the U.S. Clean Air Act Amendments of 1990 continue to be implemented and as the recent OTAG recommendations take hold in the eastern United States. This will provide a significant opportunity, through ambient air monitoring and atmospheric research before, during, and after the reductions, to understand and quantify the role of NO X in the atmosphere and in ecosystems. Changes in emissions, chemical transformations, deposition, and environmental and human health effects can be studied with an eye toward clarifying the role of NO X in the formation of ozone, acid rain, and particulate matter.