te of knowledge with respect to source-receptor relationships necessary to develop a control program on such standard or standards and additional research that is on-going or would be needed to make such a control program feasible;
             · Description of impediments to implementation of such control program and the cost-effectiveness of deposition standards compared to other control strategies including ambient air quality standards, new source performance standards and the requirements of Title IV of the Clean Air Act.
             This report fulfills the requirement of Section 404 by integrating state-of-the-art ecological effects research, emissions and source-receptor modeling work, and evaluation of implementation and cost issues to address the six areas and other issues related to the feasibility of establishing and implementing an acid deposition standard or standards. Congress also requires the National Acid Precipitation Assessment Program (NAPAP) to conduct a study similar to the technical portions of this report, on the reduction in deposition rates needed to prevent adverse ecological effects. NAPAP is required to submit its report to Congress in 1996 (Section 901[j] of the Clean Air Act Amendments).
             Developing a Standard to Protect Sensitive Resources
             An acid deposition standard is a level of deposition (most likely in units of kilograms of pollutant per hectare per year) that provides a predetermined level of protection to specific ecological resources. The natural resources most at risk from acidic deposition and those most amenable to a quantitative assessment are aquatic systems. Therefore, a standard designed to protect against the ecological effects of acidic deposition would most likely be developed based on effects to aquatic systems. Other ecological resources such as high elevation red spruce forests in the eastern United States and Canada may also be at risk, but less is known about the effects process, and the r...