Impact of global climate change on regional air quality: introduction to the thematic issue. Relative impacts of worldwide tropospheric ozone changes and regional emission modifications on European surface ozone levels. Modeling the regional effects of climate change on air quality. Nested regional climate-chemistery simulations for central Europe. Air quality in Europe during the summer 2003 as a prototype of air quality in a warmer climate. Air quality measurements in megacities: focus on gasesous organic and particulate pollutants and comparison between two contrasted cities, Paris and Beijing. Human mortality effects of concentrations of tropospheric ozone. Impacts of ozone on trees and crops.