An examination of sensitivity of WRF/Chem predictions to physical parameterizations, horizontal grid spacing, and nesting options

An accurate representation of meteorological processes is important to the accurate predictions of meteorology and air quality. In this study, the Weather Research and Forecasting model with Chemistry (WRF/Chem) is utilized to examine the sensitivity of air quality predictions to two planetary boundary layer (PBL) schemes and three land-surface models (LSMs). Model simulations with different PBL schemes and LSMs are conducted over the Houston–Galveston area for a 5-day summer episode from the 2000 Texas Air Quality Study (TexAQS-2000). Sensitivity to horizontal grid spacing (12 vs. 4 km) and nesting methods (1- or 2-way) is also studied. Model predictions are evaluated with available surface and aircraft observations. Both meteorological and chemical predictions at the surface and aloft show stronger sensitivity to LSMs than to the PBL schemes. The model predictions also show a stronger sensitivity to horizontal grid spacing using 1-way nesting than 2-way nesting and to the nesting method at 4 km than 12 km. The benefits (or disbenefits) of using more complex meteorological schemes, finer horizontal grid spacing, and more sophisticated 2-way nesting may vary and must be evaluated for specific episodes. The results from this study also indicate a need to refine model treatments at a fine grid spacing and the current 2-way nesting method used in WRF/Chem for improvement of model performance.