1.GEOGRAPHICAL ASPECTU.K.
Regarding the need for short-term actions to avoid exceedance of the 240 μg/m3 threshold, the 15 Member States can be split up into three groups:
1.In the Nordic countries (Finland, Sweden and Denmark) and Ireland no exceedances of the alert threshold happened so far (according to data reported to European Environment Agency AIRBASE) and in view of the implementation of the abovementioned long-term policy, they are even more unlikely to happen in the future.U.K.
Therefore Nordic countries and Ireland would not need to prepare short-term actions plans as there seems to be no risk of any exceedance of the alert threshold.
2.Air mass transport in north-western and central European countries is most frequently dominated by advection and often gives rise to long range transboundary pollution transport.U.K.
There are clear indications that for most parts of the north-western and central European countries exceedances of the alert threshold are diminishing. Short-term measures already in the mid-90s showed only a restricted reduction potential and implementation of the EU long-term strategy will necessitate the generalised and permanent application of some former short-term measures.
Therefore countries in which there is no significant potential for reducing the risk of exceedances through short-term action plans would not need to prepare such plans.
3.Major cities and regions in southern Member States experience, on the other hand, more often recirculation of air masses due to topography and the influence of the sea. In some cases the same air masses are recirculating several times(1). Due to high natural VOC emissions, emission reductions of VOC are relatively ineffective (so-called "NOx-limited" regime).U.K.
No significant trend of ozone peak values can be seen in the ensemble of rather limited and only recent time series. Moreover in those areas there is a lack of knowledge with regard to the efficiency of short-term measures.
Therefore cities and/or regions in southern Europe characterised by particular orographic conditions can, in principle, locally profit from short-term measures for reducing the risk or severity of exceedances of the alert value, especially for exceptional situations of extreme O3-episodes such as experienced in 2003.
For example, Millán, M.M., Salvador, R., Mantilla, E., Kallos, G., 1997. Photo-oxidant dynamics in the Western Mediterranean in summer; Results of European research projects. J. Geophhy. Res., 102, D7, 8811-8823.