The Acid Rain NOx Provisions

To address the problem of acid rain, Congress included provisions in the CAA Amendments of 1990 that were designed to reduce emissions of SO2 and NOx (see Chapter 2). The SO2 provisions, which are described in detail in the following section, set a goal for reduction of emissions by 10 million tons and then set specific caps on allowable emissions from individual facilities to achieve that goal. Unlike the SO2 provisions, the 1990 CAA Amendments set a target reduction of 2 million tons of annual NOx emissions and relied on the promulgation of emission standards on specific facilities to attain the reductions. The requirements were implemented in two phases. Starting in January 1996, Phase I required use of low NOx burner technology in tangentially and dry-bottom-wall coal-fired power plants, producing reductions in emission rates of about 40%. Phase II, which began in 2000, extended emission standards to more types of coal-fired power plants. Though generally prescriptive, the program did allow some flexibility. Companies were able to average emission rates for commonly held facilities, but intercompany trading was not allowed. Facilities that did not achieve the standard after making specified investments could appeal for alternative emission limits. The imposition of Phase I of the Acid Rain Program’s NOx performance-oriented emission standards has substantially decreased the emission rates of the affected facilities.

Maximum Achievable Control Technology

As discussed in Chapter 2, the CAA Amendments of 1990 required EPA to establish emission standards that “require the maximum degree of reduction in emissions of the hazardous air pollutants … that the Administrator determines is achievable” for sources that emit more than 10 tons per year of any listed HAP or 25 tons per year of a mixture of HAPs. In response to that mandate, EPA established standards of maximum achievable control technology (MACT) for relevant HAP sources. In principle, the standards are performance standards, because each facility is only required to match the emission rate obtained using the MACT standard, and it may use any technology. However, the manner in which MACT standards are promulgated provides an incentive for companies to opt for the sanctioned technology and thus may ultimately have the affect of a design standard (see Box 5-2).

The 1990 CAA Amendments specified that the HAP standards covering 25% of the identified categories of emission sources be issued by 1994; another 50% by 1997, and the remaining 25% by 2000. However, this schedule has not been met. The promulgation of these standards has been delayed considerably from its original time frame, proving to be a source of



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