Two-Way Coupled Meteorology and Air Quality Modeling

A two-way coupled meteorology and air quality modeling system composed of the Weather Research and Forecasting (WRF) model and the Community Multiscale Air Quality (CMAQ) model is being developed to enable simulation of multiple interactions between meteorological and chemical atmospheric processes. The two-way WRF-CMAQ system allows frequent data exchange and chemical feedback to meteorological processes. This coupled system requires "in-line" computation of meteorology-dependent processes that have previously been pre-processed such as dry deposition velocity, biogenic emissions, and point source plume rise. The WRF-CMAQ system enables consistent and easily maintainable "off-line" (sequential WRF and CMAQ simulation) and "online" (coupled) capabilities. Initial tests show significant, but sporadic and isolated differences in ground level ozone fields between off-line and on-line runs. However, tests also show very little difference between the tightest coupling (WRF and CMAQ running at the same time-step) and looser coupling where CMAQ is called every four WRF time-steps.