The U.S. EPA has developed a new comprehensive air quality modeling system, known as the Models-3 Community Multi-scale Air Quality (CMAQ) model. The CMAQ system includes a comprehensive emission processor, a Chemical Transport Model (CTM), and a meteorology model (MM5). Evaluation of the CMAQ modeling system includes simulation of a series of air quality field studies such as NARSTO and SOS. This paper describes our initial model application to the SOS/Nashville 1999 field experiment. The coincidence of a variety of sophisticated gas-phase and aerosol chemistry, and meteorological measurements from ground base in-situ, remote sensing, and airborne platforms resulted in an excellent test-bed for comprehensive model evaluation.

We are running a series of one-way nests for both MM5 and CMAQ starting with a continental 32 km resolution domain, a regional (1000x1000 km) 8 km domain centered on Nashville, and a 2 km domain covering central Tennessee. Many new features of both the meteorology and chemistry models are being debuted in this application. The meteorology runs feature the Pleim-Xiu land-surface model (PX-LSM) with indirect soil moisture data assimilation and the Asymmetric Convective Model (ACM) for PBL processes. A new dry deposition model (M3dry) has been developed as an adjunct to the PX-LSM that uses the same stomatal and aerodynamic resistances computed for evapotranspiration. New features of the CMAQ CTM include the SAPRC-99 chemical mechanism, the Modified Euler Backward Iterative (MEBI) chemical solver, and a new version of the aerosol model (AE3). The aerosol model represents size spectra by three log-normal modes with variable geometric standard deviation. AE3 adds gas-aerosol partitioning for organic reaction products and a heterogeneous reaction for N2O5 to HNO3. CMAQ also includes Plume-in-Grid (PinG) which has been updated to include aerosols. The ACM has been added as a new PBL option so that PBL mixing is consistent for meteorological and chemical species.

The SOS/Nashville 1999 field experiment will be used for evaluation of the latest version of the CMAQ system. In addition to typical comparisons to ground level chemical and meteorological observations, model evaluation will include comparisons to extensive measurements aloft by aircraft, lidar, and radar of gas-phase, aerosol, and meteorological parameters. Preliminary results from this study will be shown.