The methodology and protocol used for the construction of the master chemical mechanism (MCM) has been coupled with techniques from knowledge-based systems to develop an expert system, specifically tailored for the automatic generation of tropospheric volatile organic compound (VOC) degradation schemes. To solve the problem of automatic mechanism construction processes leading to unmanageably large mechanisms for species containing more than a few carbon atoms, strategies are developed to reduce mechanism growth. To test the mechanisms generated by the expert system, some preliminary exemplar schemes have been embedded in a simple box model to provide a comparison with the complete degradation schemes available from the MCM web site. Profiles were obtained for several of the stable and radical species. Those of the parent VOC, O-3, OH, HO2 and CH3O2 are in good agreement with profiles generated using the reference MCM schemes. Other profiles exhibited a much larger disparity, notably the sum of the peroxy radicals (RO2). These disparities provide insights for refinement of the expert system rule base. (C) 2003 Elsevier Science Ltd. All rights reserved.