Assessing ozone abatement strategies in terms of their effectiveness on the regional and urban scales

Integrated ozone abatement strategies should take into account that an emission intervention which is effective on the regional scale may not necessarily be effective for a city and its surroundings. In the context of a study performed for the European Commission a methodology was developed for assessing ozone abatement strategies in terms of their effectiveness on both the regional and the urban scale. Towards this aim, the assumptions made for three regional emission reduction scenarios were assumed to be valid also for the emission situation in the urban areas of Athens and Stuttgart and the corresponding emission inventories were compiled. The EMEP MSC-W ozone model was used to calculate the regional scale ozone distribution over a 6 month summer period applying the 1990 meteorology. Local scale transport and chemical transformation processes were analysed with the ozone fine structure (OFIS) model. Both the regional and the local scale simulations were performed for the base case (1990 situation) and the three emission reduction scenarios. The significance of regional scale emission reductions was demonstrated by the aid of a second series of simulations assuming that the emission interventions were implemented only at local scale. The results of the simulations reveal that ozone exposure in conglomerations as the ones considered in this study depends on both urban and regional scale influences. Urban VOC control is found to be effective in reducing ozone primarily on the local or urban scale, whereas urban NOx control may cause an increase of urban peak ozone while contributing to an effective reduction of regional ozone.