ENV-06-148 Looking Down the Road: Implications of EPA's New AERMOD Model for Refineries

Description:

The USEPA recently added the new AERMOD model to its guideline on air quality models (GAQM). AERMOD represents the culmination of a nearly 14-year process to develop a state of the science air quality model for short-range, local air pollutant impacts. AERMOD was designed to replace the ISCST3 model – ISCST3 has been used widely for many years for many different types of sources, including refinery sources, to evaluate local air quality impacts. EPA’s approach to AERMOD implementation includes a transition period of one year that ends in December 2006. During the transition period, EPA will allow the use of either ISCST3 or AERMOD; after December 2006, AERMOD will be required. States are approaching the implementation of AERMOD in different ways. Some states are requiring its use immediately; others are following the EPA lead and allowing the use of ISCST3 on an interim basis, and some states are considering whether to allow continued use of ISCST3 after December for state-only analyses. EPA has used AERMOD to supplement modeling for attainment demonstrations for the PM2.5 national ambient air quality standards (NAAQS), since the more complex grid models (e.g. CMAQ) are not capable of estimating concentration impacts on a local scale. This paper draws on experience using AERMOD and ISCST3 to evaluate the impacts of refinery sources, and summarizes the principal differences between the two models in terms of the effects of using the new model for refinery sources. Numerous challenges face refineries in coming years, including expansion projects, increased emphasis on planning for attainment of the PM2.5 NAAQS, issues surrounding the residual risk program, and increased visibility in the public eye of air toxics emissions due to the recently released national air toxics assessment (NATA) report. AERMOD will play a key role in the assessments that may be motivated by these programs.