A

FIGURE 4-1. Approach to emission estimation. (From AP-42, External Combustion Sources, in Emission Factors, Fifth ed., Office of Air Quality Planning and Standards and Office of Air and Radiation, U.S. Environmental Protection Agency, U.S. Government Printing Office, Washington, D.C., 1993 [latest revisions in 1998].)

more widely accepted test procedures, are assigned higher rankings, with A being the best. The emission factors rating is provided with the emission factors contained in Appendix A.

National Emission Standards for Hazardous Air Pollutants

The 1970 Clean Air Act Amendments also provided for national emission standards for hazardous air pollutants (NESHAPs). Only seven standards were established between 1970 and 1990, as the NESHAPs were the subject of numerous suits and court decisions regarding how to address emission limits on carcinogenic pollutants [4]. None of the original seven NESHAPs— asbestos, beryllium, mercury, vinyl chloride, benzene, radionuclides, and arsenic—specifically addressed coal-fired steam-generating units. The Clean Air Act Amendments of 1990 made major changes in the approach taken to address hazardous air pollutants (HAPs) with additional amendments being added as recently as May 30, 2003 [15].

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