One of the project objectives, the development of a master chemical mechanism (MCM) for the gas phase tropospheric degradation of 120 volatile organic compounds is presented.
Introduction to the MCM
Development and construction of a detailed chemical mechanism to describe the complete tropospheric oxidation of 120 volatile organic compounds (VOC) is presented. The VOC which are degraded in this mechanism were selected on the basis of available emissions data(2), and provide approximately 97% mass coverage of the emissions of uniquely identifiable chemical species. The degradation schemes have been constructed using the methodology described in an earlier publication(3). A brief review of the ideas behind the protocol document are given here
The degradation schemes are currently being used to provide an up to date mechanism for the production of secondary oxidants, for use in a model of the boundary layer over Europe. 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 simulation of secondary pollutant formation for a range of NOx or VOC emission scenarios. These schemes are believed to be particularly appropriate for comparative assessments of the formation of oxidants, such as ozone, from the degradation of organic compounds.
Compilation of the individual VOC degradation schemes has produced the Master Chemical Mechanism (MCM). The organic component of the MCM contains in the region of 7000 reactions and 2500 chemical species. With the exception of 18 aromatic compounds, the chemistry was constructed using the protocol described previously(3). The aromatic chemistry was based on that used in previous work(1,4), but was extended to include the reactions of peroxy radicals with HO2 and NO3, and the permutation reactions of the peroxy radicals. Although there are currently many gaps and uncertainties in the details of the atmospheric degradation mechanisms of aromatic compounds(5), there are several groups active in this field of research(6,7), and new data are constantly emerging.
The difficulties associated with ensuring that there was no species or nomenclature duplication within the compiled mechanism, led to the development of computerised mechanism construction. Details of the format and operation of the computerised system are described herein. Also, due to the large size of the MCM, it is not possible to provide the listing in hard copy. Full facsimile coding is available, together with associated mechanism and species files via e-mail and the Web. The concepts behind the methodology of the mechanism development and construction are such that as new data becomes available the MCM can be updated, utilising the computer aided construction format.
The completed MCM has been coded and fully integrated using Facsimile, within the UK photochemical trajectory model(4), to assess regional scale ozone formation across north west Europe and the British Isles. A Photochemical Ozone Creation Potential (POCP) index is being generated from the model results showing the relative importance of each VOC in ozone formation, on a mass emitted basis.
More details can be found on the site.
Summary by 李晓霞 on 2002-11-08
Last updated by 李晓霞 on 2002-11-08