Model calculations of present and future levels of ozone and ozone precursors with a global and a regional model

Levels of key chemical pollutants in the atmosphere are calculated for present (1996) and future (2010) emission scenarios with the help of a global model (Oslo CTM2), and a regional model (EMEP Eulerian Photochemistry model) centered over Europe. Both models are three-dimensional (3D) Eulerian models and describe atmospheric transport based on the actual meteorological conditions for 1996. Boundary values of the chemical species for the regional model integrations are supplied by the global model. This paper assesses the importance of long-range Northern Hemispheric transport of ozone and its precursors to calculated concentrations at different height levels over Europe. Calculated 1996 ozone (O-3) levels show good accordance with measurements for most of the year, but with a tendency to overestimate O-3 at coastal cites. Sensitivity studies have been made with 2010 emission scenarios based on current legislation and reduction plans for Europe and USA, and IPCC scenario WP92a for the rest of the world. Significant reductions in emissions are expected in Europe and North America while increases are expected in other areas, and in particular over Southeast Asia. Model results show a general increase of the global tropospheric ozone levels with significant regional differences. Over Europe, an increase of free tropospheric ozone levels of the order of 10 ppbv can be expected in summer, resulting in boundary layer ozone levels over Europe of the order of 2 ppbv higher than with present free tropospheric levels. Even so, it can be expected that the ozone threshold values in Europe will be much less Frequently exceeded in the future as a result of the foreseen reductions in the European emissions of ozone precursors. (C) 2000 Elsevier Science Ltd. All rights reserved.