The session focuses on the variability of the tropospheric and stratospheric chemical composition on diurnal, seasonal and longer timescales and looks at the processes driving this variability. Special emphasis is put on the scientific value of high-quality long-term measurement data sets and supporting model simulations. Both approaches contribute to improved understanding of the mechanisms that control the variability of atmospheric chemical composition (including multiple gaseous species). Presentations related to the projections of the atmospheric composition are welcome in this session as well.
Researchers are invited to present novel scientific results from mid- and long-term observational time series from various programmes and networks such as the Global Atmosphere Watch (GAW) Programme, European Monitoring and Evaluation Programme (EMEP), Network for the Detection of Atmospheric Composition Change (NDACC), Southern Hemisphere Additional Ozonesondes (SHADOZ), Advanced Global Atmospheric Gases Experiment (AGAGE), National Oceanic and Atmospheric Administration (NOAA), regular airborne (e.g. CARIBIC, IAGOS, CONTRAIL) and other campaigns as well as satellite data and model simulations. Data relevant to tropospheric and stratospheric composition, in particular related to ozone depletion, climate change and air quality as well as firn data on past atmospheric composition are welcome. We welcome contributions from multi-year modeling studies and inter-comparison exercises which address past and future tropospheric or stratospheric composition changes, carried out in the framework of international projects and initiatives. The session will be dedicated in particular to the celebration of the 30th anniversary of the GAW Programme.