THE TROPOSPHERIC DEGRADATION OF VOLATILE ORGANIC-COMPOUNDS - A PROTOCOL FOR MECHANISM DEVELOPMENT

Kinetic and mechanistic data relevant to the tropospheric oxidation of volatile organic compounds (VOCs) are used to define a series of rule s for the construction of detailed degradation schemes for use in nume rical models. These rules are intended to apply to the treatment of a wide range of non-aromatic hydrocarbons and oxygenated and chlorinated VOCs, and are currently being used to provide an up-to-date mechanism describing the degradation of a range of VOCs,and the production of s econdary oxidants, for use in a model of the boundary layer over Europ e. The schemes constructed using this protocol are applicable, however , to a wide range of ambient conditions, and may be employed in models of urban, rural or remote tropospheric environments, or for the simul ation of secondary pollutant formation for a range of NOx or VOC emiss ion scenarios. These schemes are believed to be particularly appropria te for comparative assessments of the formation of oxidants, such as o zone, from the degradation of organic compounds. The protocol is divid ed into a series of subsections dealing with initiation reactions, the reactions of the radical intermediates and the further degradation of first and subsequent generation products. The present work draws heav ily on previous reviews and evaluations of data relevant to tropospher ic chemistry. Where necessary, however, existing recommendations are a dapted, or new rules are defined, to reflect recent improvements in th e database, particularly with regard to the treatment of peroxy radica l(RO(2)) reactions for which there have been major advances, even sinc e comparatively recent reviews. The present protocol aims to take into consideration work available in the open literature up to the end of 1994, and some further studies known by the authors, which were under review at that time. A major disadvantage of explicit chemical mechani sms is the very large number of reactions potentially generated, if a series of rules is rigorously applied. The protocol aims to limit the number of reactions in a degradation scheme by applying a degree of st rategic simplification, whilst maintaining the essential features of t he chemistry. These simplification measures are described, and their i nfluence is demonstrated and discussed. The resultant mechanisms are b elieved to provide a suitable starring point for the generation of red uced chemical mechanisms. Copyright (C) AEA Technology. Published by E lsevier Science Ltd