This document was prepared to describe the ozone air quality modeling performed by EPA in support of the Mobile Source Air Toxics (MSAT) rule. Included is information on (1) the air quality modeling and the development of model inputs, (2) the performance of the models as compared to measured data, and (3) an assessment of the expected air quality improvements from the VOC emissions reductions that are part of this proposal. Because of the availability of reductions from different precursor pollutants and types of sources, applying the model for individual chosen control scenarios may miss alternative strategies that achieve greater air quality benefits at a lower cost. As a result, a new approach known as air quality metamodeling has been developed to aggregate numerous individual air quality modeling simulations into a multi-dimensional air quality 'response surface'. Simply, this metamodeling technique is a 'model of the model' and can be shown to reproduce the results from an individual modeling simulation with little bias or error. This approach allows for the rapid assessment of air quality impacts of different combinations of emissions reductions and was used here to project the effects of the portable fuel container controls within the MSAT rule.

Project officer: Pat Dolwick. February 2007. EPA 454/R-07-003.