In addition to focusing on criteria pollutant transport dynamics, the scope of EPA’s multistate transport responsibilities should include HAPs and the adoption of mitigation measures to address ecosystem and welfare impacts.

Recommendation Three

Transform the SIP process to meet future air quality challenges.


The SIP process has been an important component of the nation’s AQM system (see Chapter 3). It allows state and local agencies to account for emission controls adopted at the federal and multistate level and then to choose additional local emission-control measures to attain NAAQS. On balance, this division of responsibility should be appropriate. It can also be the basis of a constructive partnership between the federal and state governments that steadily improves air quality on local, multistate, and national scales. In fact, air quality monitoring data confirm that such improvements have occurred in the past two decades.

Nevertheless, important adjustments to the SIP process are needed if the difficult challenges ahead are to be addressed effectively. As discussed in Chapter 3, the major concerns are described below:

  • The SIP process places too much emphasis on the development of a one-time NAAQS “attainment demonstration.” Because of the significant scientific, political, and legal uncertainties inherent in such an exercise, it should not be expected to be an accurate predictor of future air quality.

  • The SIP process has mandated extended amounts of local, state, and federal agency time and resources in an iterative, often frustrating, proposal and review process that focuses primarily on compliance with intermediate process steps and not on the more germane long-term indicators of performance.

  • Each SIP is developed for a single criteria pollutant in isolation from other SIPs developed in the same location for other criteria pollutants, making it difficult for SIPs to pursue multipollutant, source-based strategies.

  • The SIP process does not provide mechanisms to integrate control strategies for noncriteria pollutants (HAPs) that can be emitted from many of the sources that emit criteria pollutants.

  • The SIP process lacks methods for identifying and acting on air pollution hot spots, where populations are exposed to significantly high concentrations of air pollutants from one or multiple sources.

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