a result of the imposition of NOx emission standards on new motor vehicles (see Chapter 4) and then inched upward for the remainder of the 1980s.
Acid rain gradually emerged as a serious environmental concern in the late 1970s. A growing body of scientific evidence had accumulated that documented the deleterious impacts of acid rain on ecosystems, aquatic life, and property, particularly in regions where soils are acidic, such as eastern Canada and the northeastern United States. Pressure for remedial action began to build from environmental groups and officials from the northeastern states most affected by acid rain. The Canadian government also began to pressure the United States, claiming that its ecosystems were being damaged from the transport of acid rain precursors from the United States.
In response, Congress created the National Acid Precipitation Assessment Program (NAPAP) in 1980 to study the impacts of acid deposition, recommend if emission controls were needed to mitigate these impacts and, if so, the magnitude of the emission reductions needed (see Box 2-1). Ten years
The National Acid Precipitation Assessment Program (NAPAP) was established by Congress to study the impacts of acid deposition, recommend if emission controls were needed to mitigate these impacts, and, if so, the magnitude of the emissions reductions needed.
A major endeavor of NAPAP was the development of the regional acid deposition model (RADM) (Chang et al. 1987), a state-of-the-science 3-dimensional grid model capable of simulating the physical and chemical processes leading to the formation and deposition of acidic speciesa (NAPAP, 1991a). Model development started in 1983 and its application was completed in the early 1990s. The model (together with similar tools like the ADOM model developed for Canada) provided important insights into the source-receptor relationships of the acid deposition problem in the United States. However, these modeling exercises (together with the rest of the synthesis of the acid deposition research) came to fruition very close to the time of the completion of the CAA Amendments of 1990 and appear to have played a minor role in the development of the acid rain provisions in the 1990 Amendments. Instead it appears that a complex set of technological, legal, and political considerations played the most critical roles in shaping the emission targets for the acid rain program in the 1990 Amendments. These other considerations included the technological and economic feasibility of reducing emissions as well as the need to reach consensus on a regionally and politically divisive issue.