Keywords: ISCST, ISC-PRIME, AERMOD, CALPUFF, guideline, air quality, models, permits, regulations, United States
Managing air quality during regulatory changes
This paper discusses the regulatory and technical issues associated with the revisions to the US EPA Guideline on Air Quality Models. The proposed guideline includes the models AERMOD, CALPUFF, and ISC-PRIME, all of which contain significant technical improvements over prior models. Differences in modelling requirements are appearing as regulatory agencies and industries use technically superior but unapproved models prior to publication of 'final rules'. The more than two-year delay of the 'final rules' has meant that most sources continue to be analysed using the ISCST model for short-range effects. However, on an individual basis some applicants and agencies have been requesting the use of AERMOD and/or ISC-PRIME. For long-range transport analyses such as visibility/regional haze, Class I area increment, and acidic deposition, the CALPUFF model is now widely used. Moreover, several revisions have been made in both AERMOD and CALPUFF over the past two years. Without the 'final rules', dispersion modelling is susceptible to nonuniform practices when applying models to permit applications.