toward data collection and research. Although pollution emissions have been reduced substantially, the emphasis on criteria pollutants might or might not be justified on a continuing basis in terms of actual human health and ecosystem risk.

• A consequence of the current emphasis on criteria pollutants is that resources to study and characterize HAPs are insufficient. Systematic ambient air monitoring of most HAPs has been nearly absent, further hindering the development of appropriate health assessments and control strategies.

• The list of regulated HAPs has been far too static. There have been no periodic reviews to consider additional compounds for inclusion and to consider the possibility of adding certain HAPs to the criteria pollutant list.⁸

Second, the system, as currently administered, has hindered the development of management strategies that apply a multipollutant approach to addressing the most significant risks:

• The classification has become too rigid and inflexible, creating institutional barriers to change as more is learned about individual pollutants. For example, some pollutants listed as HAPs are ubiquitous in the environment and of substantial health concern (such as benzene) and might be treated more appropriately as criteria pollutants.

• The classification scheme assigns pollutants to regulatory regimes that might or might not be optimal for each pollutant. For example, although mercury is classified as a HAP, it is widely dispersed in the atmosphere, creating diverse exposure, and thus might be more appropriately regulated by a cap-and-trade program (see Chapter 5). On the other hand, many HAPs can create hot spots in specific locations. Mitigation of these types of pollutants might be facilitated by an AQMP regulatory approach with input at the state and local levels.

• The current regulatory framework—with its diverse systems for controlling the two types of pollutants and its failure to require HAPs to be considered at all in local and state air quality planning—makes it difficult to create an integrated multipollutant management approach for criteria pollutants and HAPs, even when they share sources, and local populations and ecosystems are exposed simultaneously to both.

• Even among the criteria pollutants, the practice of setting NAAQS for each pollutant separately, with the attendant differences in the timing of standard setting and attainment deadlines, creates a substantial barrier to integrated multipollutant planning at the state and local levels.