“unreasonably delayed” (CAA § 304(a)(2), 42 U.S.C. § 7604(a)(2)). The courts have vigorously implemented this authority in the past to mandate, for example, a schedule for EPA action (Melnick 1983).

The nation’s AQM system may be conceptualized to operate in a variety of ways to meet the goals and requirements set forth in the CAA. The committee chose a model that describes the system’s operation in terms of four broadly defined sequential activities (Figure 1-3). The first three are the following:

• Setting air quality standards and objectives (either in the CAA or by EPA).

FIGURE 1-3 Idealized schematic showing three of the four sequential activities carried out by the nation’s air quality management system. The fourth iterative activity involves a return to activities 1 and/or 2 to account for new information to correct deficiencies identified in step 3. Bullets under each heading provide examples; listings are not necessarily comprehensive.