To address these deficiencies, the nation’s AQM system must begin the transition toward a risk-focused multipollutant approach to AQM. Several recommendations to initiate this transition are presented below.
Many HAPs warrant increased resources for monitoring and research so that the risk HAPs pose to human health and welfare can be more accurately assessed and given the regulatory attention needed to protect human health and welfare. However, the statutory list of HAPs is long and may need to be expanded. It is unrealistic to expect that all HAPs can be monitored on a routine basis or that all HAPs can be placed under an aggressive regulatory framework. To ensure an appropriate allocation of resources and regulatory attention to the most dangerous HAPs, the committee recommends that the current system of setting priorities, embodied in EPA’s urban air toxics program (EPA 2000b), be continued and enhanced. One possible approach (using a three-tier system to set priorities) is described in Box 7-3 for illustrative purposes. Other approaches might involve further elaboration of EPA’s current list of 33 high-priority HAPs and a focus on ensuring that comprehensive strategies to monitor and address the sources of these pollutants are created and integrated into state and local AQMPs.
Beyond the current list of HAPs, little information on a vast array of unregulated emitted substances is an important problem. Examples of such possible toxicants are substitutes for various toxicants, such as bromopropane, used as a substitute for tetrachloroethylene and flame retardant polybrominated diphenyl ethers; atmospheric transformation products, such as formylcinnamaldehyde; peroxyacyl nitrates; other oxides, such as 1,3-butadiene diepoxide and benzoic acid; vehicular emissions, such as 2-methylnapthalene, diesel exhaust mixture, polychlorinated dibenzodioxins, polychlorinated dibenzofurans, isobutylene, and black carbon; and a number of pesticides.
Especially for high-volume emissions and hot spots, some reasonable level of regulatory response appears appropriate to curtail exposure to unregulated chemicals with suspicious but unproved adverse impacts. The committee recommends that suspicious chemicals emitted above a certain threshold concentration be tracked through a listing process and that a system for further addressing such chemicals be explored (see Box 7-4).