mentation, compliance assurance, and progress evaluation. Stratospheric O3 protection and greenhouse gas emission control were not included in the scope of the study except in regard to strategies in tropospheric air quality control programs to control emissions.

A wide range of external factors beyond the scientific and technical aspects of air quality can drive the character and effectiveness of an AQM system and are relevant to our review. Governmental policies on economic growth, energy production and use, transportation, and land use, for example, affect pollutant emissions and can therefore reinforce or frustrate AQM policies. Decisions and practices of consumers concerning the technologies and products they purchase and use also affect pollutant emissions.

Legal and institutional factors also affect the implementation of AQM. Most important, the nation’s federal system of government, with specific authorities assigned to the federal government and others to the states, limits the kinds of regulatory structures that can be used to administer the AQM system in the United States. For example, although air pollution issues often demand regional controls, all such controls can only be enforced at the state or federal levels.

It is beyond the scope of this report to comprehensively analyze these external factors and assess how they could be changed to enhance the effectiveness of the nation’s AQM system. However, at each stage in considering implementation of the CAA, the committee attempted to take into account the degree to which these larger factors could reduce the effectiveness of specific control measures (for example, the growth in travel and its relation to automobile emission standards). The committee found that considerable progress in air quality improvement has been accomplished in the United States over the past 2-3 decades even in the face of these confounding external factors. Thus, the recommendations advanced here tend to be evolutionary in nature and do not involve a major overhaul of the AQM system.


To provide a basic foundation for conclusions and recommendations, the committee reviewed and critiqued the key elements of the CAA and the concomitant methods and approaches to manage air quality in the United States. The discussion in Chapter 2 focuses on how standards and goals are set. Chapter 3, 4, and 5 describe the design and implementation of control strategies adopted by federal, regional, state, and local governments. Chapter 6 discusses how progress in meeting the AQM goals is measured, particularly with respect to health and ecosystem outcomes. After consideration of the major air quality challenges facing the nation in the coming

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