The U.S. Environmental Protection Agency (U.S. EPA) is extending its Models-3/Community Multiscale Air Quality (CMAQ) Modeling System to provide detailed gridded air quality concentration fields and sub-grid variability characterization at neighborhood scales and in urban areas. CMAQ is an advanced air quality modeling system that embodies a "one-atmosphere," multiple-pollutant philosophy. The meteorology model used with CMAQ in this application is the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5).

For fine-scale urban simulations (~1 km horizontal grid spacing), MM5 has been modified to include an urban canopy parameterization that accounts for the drag exerted by the urban structures on the flow, the enhancement of turbulent kinetic energy (especially near the tops of the buildings), and the energy budget at the street level and between buildings. This refinement of MM5 is targeted to provide CMAQ with the means to capture details of pollutant spatial distributions at these scales.

This presentation will describe the urban canopy parameterization and various sensitivities in an application to a high-ozone episode.