The funding of health effects research and the subsequent selection and review of this research in criteria documents and staff papers used to promulgate NAAQS often lack a coherent and standardized strategic plan.
The CAA requirements for pollutant-specific air quality standards for criteria pollutants and HAPs have encouraged the evolution of an AQM system with control strategies that largely focus on one pollutant at a time. Changes that foster multipollutant approaches would be advantageous. One method that could be considered would be to assess the health and welfare effects of sources instead of pollutants.
The list of HAPs (that is, those specifically regulated by EPA) has been essentially static for a decade and probably does not contain all the air toxics that pose a significant risk to human health and welfare.
Current monitoring data and understanding are not sufficient to adequately assess the relative risks to human health and welfare posed by exposure to the myriad pollutants in the environment, as well as to the myriad microenvironments or hot spots in which these exposures may occur. Development of such a capability will be a major challenge and will require a substantial investment in resources for monitoring and effects research over a long period of time.
Although progress has been made to improve exposure assessment and to link specific exposures and effects to specific sources, substantial additional work is needed.
Indoor air pollution poses a significant health risk to humans and yet is not addressed comprehensively by any agency in the federal government.
The current practice of letting the primary standard serve as the secondary standard for most criteria pollutants does not appear to be sufficiently protective of sensitive crops and unmanaged ecosystems. Moreover, concentration-based standards are inappropriate for some resources, such as soils, groundwater, surface water, and coastal ecosystems, that are at risk from the indirect effects that pollutants can foster (for example, eutrophication). A deposition-based standard would be more appropriate in some instances.
It is a significant challenge to set ambient or emission standards to protect public health with an adequate margin of safety from harmful exposure to a pollutant if that pollutant does not exhibit a threshold concentration for an adverse health effect.
Recommendations that address these limitations are provided in Chapter 7.