The Earth’s atmosphere has been changing rapidly over the last decades. Many national and international research programmes have been set up to investigate the atmospheric variability and changes. Europe has played a key role in this effort. Currently, various phenomena are understood, but many questions still remain unanswered, for example:

Will the actually observed polar ozone loss and mid-latitude ozone decrease be confirmed?

Will the ozone layer recover as expected following the turnover of halogen loading?
-- Do we understand the bromine budget?

What will be the climatic impact of the above phenomena?

How important are the exchanges and interactions between troposphere and stratosphere?

What will be the evolution of the UV irradiance reaching the Earth’ surface?