systems from air pollutants, such as sulfur, nitrogen, or mercury. For such resources, a deposition-based standard would be more appropriate (see Chapter 2).
EPA should undertake a comprehensive review of the need and use of standards to protect public welfare.
The nation’s AQM system has not been able to build a cohesive program capable of reliably reporting the status and trends in exposure and ecosystem conditions across regions and the nation (see Chapter 6).
Specific activities are recommended that will help EPA to establish measures and actions to more effectively protect public welfare:
Develop and implement networks for comprehensive ecosystem monitoring. Networks for monitoring terrestrial and aquatic ecosystem structure and function are needed to quantify the exposure of natural and managed resources to air pollution and the effects of air pollutants on ecosystems.
Establish acceptable exposure levels for natural and managed ecosystems. On an ongoing basis, EPA should evaluate current research on the effects of air pollutants on ecosystems as a means to establish acceptable exposure levels for both natural and managed resources. In setting these acceptable exposure levels, EPA should consider the relevant geographic dimensions and sensitivity of the various resources to determine if acceptable exposure levels vary regionally. The adequacy of resource-specific acceptable exposure levels should be reviewed and revised, if necessary, at least every 10 years.
Promulgate secondary standards. From the improved understanding gained from the above two actions, secondary standards should be promulgated where appropriate. In some cases, deposition-based secondary standards may be preferable to concentration-based standards. If acceptable exposure levels vary significantly from one region of the nation to another, consideration should be given to the promulgation of regionally distinct secondary standards.9
Design and implement controls. Within the context of EPA’s recommended enhanced responsibility and authority for addressing multistate air
A move to regional secondary standards may require an amendment of the CAA. The courts have held that the primary NAAQS must be met on a nationwide basis. It is possible, however, that a court would find that a standard designed to protect the public welfare did not have to be uniform throughout the country, even though a standard designed to protect public health must be uniform. See Lead Industries Ass’n v. EPA, 647 F.2d 1130 (D.C. Cir. 1980).