Comparison of the chemical schemes of the EMEP MSC-W and IVL photochemical trajectory models

This article describes the results of a chemical comparison between the 140-reaction EMEP MSC-W chemical scheme and a much more comprehensive chemical mechanism, the IVL scheme with over 1800 reactions between 714 species. The schemes have been compared in detail for three different emission scenarios. One scenario describes the air in a London plume and the others correspond to more moderately polluted air masses typical of regional scale ozone formation. Comparisons of the simulated concentrations of ozone have been further conducted in an isopleth of chemical environments where the emissions of NOx and VOC have been varied over a wide range. The simulated concentrations of ozone and most photochemical species are found to compare well with the chemical descriptions for all scenarios. This analysis differs from similar previous comparisons in that (1) we investigate the changes in ozone resulting from changes in emissions of nitrogen oxides and groups of hydrocarbons, i.e. alkanes, alkenes, aldehydes, alcohols and aromatic species, and (2) we analyse the main mechanisms underlying the model results in order to illustrate how the similarities and differences of the two schemes influence the ozone simulations. Overall we conclude that the EMEP chemistry gives a description of ozone formation and the effects of emission control measures which is in good agreement with that given by the much more comprehensive IVL chemistry.