Impact of Aerosol Direct Effects in the Community Multiscale Air Quality (CMAQ) Model Version 5.0

The latest release version of the Community Multiscale Air Quality (CMAQ) model includes the ability to simultaneously run the CMAQ and the Weather Research and Forecasting (WRF) models, which allows for feedback between the two models. In previous versions of the CMAQ model, the meteorological fields were required to be created prior to performing the CMAQ simulation, and therefore no feedback between the two models was possible. Feedback between the air quality and meteorological models is important for accurately simulating the effect that changes in air quality have on the meteorological fields, and vice versa. In this study, the coupled WRF/CMAQ system is used to simulation the entire year 2006 with aerosol direct effects included. The results from the coupled WRF/CMAQ simulation are compared to a similarly configured un-coupled WRF/CMAQ simulation for the same time period. The difference between the two simulations highlights the impact that aerosol direct effects have on the radiative forcing in the meteorological, which in turn affects both the meteorological and air quality fields. The results of the two simulations are compared against each other (model-to-model) to assess the major impacts to the model estimates and to available surface and upper-air (e.g aircraft) measurements (model-to-observation) to assess the impact on operational model performance.