Simulating climate-air quality interactions presents one of the major challenges in quantifying the impacts of urban/regional air pollution on climate change. In this study, a unified Global-through-Urban Weather Research and Forecasting Model with Chemistry (GU-WRF/Chem) being developed at North Carolina State University is applied to simulate climate-air quality interactions from regional to global scales. Simulations with meteorology only and with both meteorology and chemistry will be conducted for 2001 over three domains including a global domain at a horizontal grid resolution of 4˚ (Lat) × 5˚ (Lon), a Trans-Pacific domain covering Asia, a portion of Pacific, and North America at 1.08˚ (Lat) × 1.08˚ (Lon), and the continental U.S. at 0.36˚ (Lat) × 0.36˚ (Lon). Model simulations will use a gas-phase chemical mechanism that is a revised Carbon Bond Mechanism (CB05) for global applications (referred to as CB05 for global extension (CB05GE)), the Modal Aerosol Dynamics Model for Europe/the Secondary Organic Aerosol Model (MADE/SORGAM), the Regional Acid Deposition Mechanism (RADM) aqueous-phase chemical mechanism, and the Fountoukis and Nenes aerosol activation module. Model evaluation using surface and satellite data will be conducted to assess the model capability in reproducing meteorological and chemical observations. Comparison between simulations with meteorology only and with both meteorology and chemistry will quantify the feedbacks of gases and aerosols to simulated meteorology, radiation, and cloud condensation nuclei (CCN) as well as associated seasonalities of such feedbacks. Simulations with 1- and 2-way nesting will also be conducted to examine the sensitivity of the feedbacks between global and nested regional domains to nesting methods.