Modelling

The chemistry of the atmosphere is controlled by a large number of complex chemical and physical processes. The study of such a complex system requires the use of numerical models, which have improved substantially over the past ten years. These models are mathematical representations of the main physical and chemical processes controlling the spatial and temporal distributions of trace gases and aerosol particles. The models have been developed to test our understanding of the atmospheric processes, to identify key variables and important interactions, and to interpret local, regional, and global observations. Additionally, they can be used to simulate global distributions of tropospheric compounds, predict the evolution of the chemical state of the atmosphere and of the radiative forcing of climate in response to natural or anthropogenic perturbations, provide an optimal use of satellite data through data assimilation, and help policymakers define emission reduction policies.