Tropospheric ozone plays an important role in the Earth atmospheric processes as an important oxidant and short lived climate forcing gas. It is also a pollutant affecting human health and ecosystems. Observed levels of the tropospheric ozone have increased over the last 30 years. The attribution of this increase is a complicated task as ozone can be formed in one region and due to long-range transport affect others far away from its origin. In addition stratospheric ozone can be mixed into the troposphere and thus contribute to the interannual variability and to the long-term changes in tropospheric ozone (including aspects of upper troposphere/lower stratosphere processes). This session invites contributions addressing trends in tropospheric ozone derived from observations and models. Analysis of climate change, transport, emissions, dry deposition and chemical oxidative processes that have direct and indirect effect on tropospheric ozone variability are of interest to this session.