may not be justified on the basis of actual human health and ecosystem risk. Similarly, it is not clear if all of the currently regulated HAPs pose a greater risk to human health and welfare than many of the untested and unregulated air toxics known to be in the ambient air and at specific hot spots.
For the reasons noted above, it would be highly desirable for the nation’s AQM system to have a robust risk-assessment capability that could reliably assess and set priorities on the relative risks posed by all pollutants in the atmosphere—in hot spots and microenvironments, as well as the ambient air. However, although the scientific community has learned a great deal about air pollution in recent decades, and there have been significant advances in the general field of risk assessment (NRC 1994), current knowledge is not yet extensive enough to rank pollutants comprehensively on the basis of risk. There is a lack of sufficient knowledge of the diversity of health and welfare effects associated with different pollutants, and, perhaps more important, with different mixtures of pollutants under environmental conditions. Another major deficiency is our inability to assess pollutant exposures accurately because of a lack of sufficient data on the distribution of pollutants. If these deficiencies are to be addressed, substantial investments over a substantial period of time will be needed for research on air pollution effects research and for more advanced systems to determine the spatial and temporal variability of air pollutants in specific hot spots and in indoor environments as well as the ambient air.
The establishment of the NAAQS has allowed for important and extensive input and feedback from the scientific and technical communities and has catalyzed additional research and understanding of the effects of air pollution.
The standards-setting procedure for NAAQS has been responsive to new scientific information and has allowed for adjustments in the standards when scientific understanding so dictated.
The establishment of NAAQS has provided targets for regulatory agencies and measures by which to assess improvement in air quality and the effectiveness of the AQM.