The chemical mechanism generation programme CHEMATA-Part 1: The programme and first applications

The chemical mechanism generation programme CHEMATA (CHEmical Mechanism Adaptation to Tropospheric Applications) generates explicit or lumped gasphase chemical mechanisms. Input data are a list of species and their source strengths (emissions or atmospheric production), kinetic data and lumping group definitions. All these input data can be changed by the user in order to generate a mechanism which is adapted to the needs of the user and to the conditions of the modelling area. The programme converts the information about the chemical structure of each species into a number code which contains all necessary information about the atoms of this molecule and the way they are connected to each other. For describing a chemical reaction the code is modified in a well-defined way which corresponds to the change in the molecule structure which in reality occurs during this reaction. This number code is also used to identify species for which experimental kinetic data are available or for employing structure-reactivity relationships for estimating kinetic data. To enable lumping to be as flexible as possible all organic mechanism species can be defined by their functional groups, their reactivity, and their chain lengths. CHEMATA compares these definitions with the number codes of the real species in order to determine the correct lumping group for each real species. Then the lumped mechanism is produced considering the source strengths of all real species. As an application of CHEMATA two sensitivity studies were performed: one on the influence of species lumping by extending and reducing the regional atmospheric chemistry mechanism and the other on the influence of updating the kinetic data for the kinetics of oxy radical reactions.