1. UNECE/CLRTAP Task Force on Hemispheric Transport of Air Pollution Policy-Relevant Science Questions André Zuber European Commission

2. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 1. How does hemispheric transport affect air pollution ? What processes and which pollutants (ozone, Hg, POPs, PM …)? What evidence from observations and models? What pathways by source region and season? What processes need to better known? How do processes on the hemispheric scale affect processes on the local and regional scale?

3. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 2.How much air pollution from one country or region to another? What evidence from observations? What source-receptor relationships from models? What model resolution is needed? How may models be nested from global to local scale? What improvements of models are needed?

4. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 3.How much may air pollution change due to emission changes? Are there simple relationships between emission changes and air pollution? How may the source-receptor be infleunced by the resolution of the models?

5. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 4.How may the source-receptor relationships change over the next 20 to 50 years? Projected emission changes over different regions? How to construct air emission scenarios?

6. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 5.How may the source-receptor relationships change due to global change? Changes of the atmosphere including climate change? Significant feedbacks between air pollution and global change including climate change?

7. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 6.How confident are we of the results and what is our best estimate of the uncertainties? What techniques for evaluation of models? What observation data is needed to evaluate models to increase confidence? What data is available to track long term changes? Which processes need to better understood to the models? What is our requirement of minimum level of certainty?

8. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions 7.What efforts are needed to develop an integ- rated system of observation data and models?

9. UNECE/CLRTAP TF HTAP Policy-Relevant Science Questions Task Force on Hemispheric Transport of Air Pollution: What issues in TF HTAP? Priorities and in what order?

10. Thank you André Zuber European Commission