This document describes the air quality modeling performed by EPA in support of the proposed Tier 3 standards. A national scale air quality modeling analysis was performed to estimate the impact of the proposed fuel and vehicle standards on future year levels of annual and 24-hour PM2.5 concentrations, daily maximum 8-hour ozone concentrations, annual nitrogen dioxide, annual nitrogen and sulfur deposition, annual ethanol and select annual and seasonal air toxic concentrations (formaldehyde, acetaldehyde, benzene, 1,3-butadiene and acrolein) as well as visibility impairment. To model the air quality benefits of this rule we used the Community Multiscale Air Quality (CMAQ) model.1 CMAQ simulates the numerous physical and chemical processes involved in the formation, transport, and destruction of ozone, particulate matter and air toxics. In addition to the CMAQ model, the modeling platform includes the emissions, meteorology, and initial and boundary condition data which are inputs to this model.

Project Officer: Sharon Phillips. Includes bibliographical references. Revision of EPA-454/R-13-001, published in March 2013; Appendix D was revised in June 2013. "March 2013". "EPA-454/R-13-006".