CHASER: A global chemical model of the troposphere 1. Model description

We present a new global three-dimensional chemical model for the troposphere, named CHASER (CHemical AGCM for Study of atmospheric Environment and Radiative forcing). This model, developed in the framework of Center for Climate System Research/National Institute for Environment Studies (CCSR/NIES) atmospheric general circulation model (AGCM), is aimed to study tropospheric photochemistry and its influences on climate. The chemical component of the model simulates the O3-HOx-NOx-CH4-CO photochemical system and oxidation of nonmethane hydrocarbons through 88 chemical and 25 photolytic reactions with 47 chemical species in its present configuration. The model includes emission sources, dry and wet deposition as well as chemical transformations. Meteorological processes such as transport due to advection, convection, and other subgrid-scale mixing are simulated “on-line” by the dynamical component of the CCSR/NIES AGCM. A detailed evaluation of the model results is presented in a companion paper [Sudo et al., this issue]. An evaluation of the transport scheme adopted in the model suggests that the model is capable of simulating transport associated with convection and boundary layer mixing as well as large-scale advection. The model capability to simulate dry and wet deposition was also evaluated by conducting a simulation of atmospheric lead. The simulated lead distributions are consistent with those observed at the surface, showing the validity of the deposition parameterization adopted in the model.