Gaseous and particulate trace constituents effect the earth's radiative budget and therefore climate. Concerning trace gases the directly effective greenhouse gases like carbon dioxide (CO2), methane (CH4) and dinitrogen oxide (N2O), and those having an indirect influence on climate, as carbon monoxide (CO) and nitrogen oxides (NO, NO2), are distinguished. The release of CO, NO and NO2 followed by photochemical processes in the atmosphere results in the formation of the secondary greenhouse gas ozone (O3), and undergoing complex reaction schemes it influences the destruction of the directly emitted greenhouse gases. The main sources for carbon monoxide and nitrogen oxides are traced back to anthropogenic activities (burning of fossil fuel in the industrial areas of the Northern Hemisphere and of biomass in the tropics). Most of the particulate emissions are caused by anthropogenic activities as well. They change the radiative budget in a direct way and by modifying the cloud properties of climatic relevance.
Especially in the tropopause region between about 8 to 15 km altitude the radiative budget of the earth is very sensitive to any change in the trace gas concentrations. However, the knowledge on sources and sinks of trace constituents of climatic relevance is quite poor for this specific height interval. The institute contributes to an improvement by performing several research projects. The European projects EULINOX and TROCCINOX deal with the formation of nitric oxides caused by electrically active thunderstorms in mid latitudes and in the tropics, respectively. The vertical lift of trace constituents from the boundary layer to the upper troposphere caused by deep convection and frontal systems is research topic of the projects CONTRACE and VERTIKATOR. The wash out of nitric acid, the most important atmospheric sink for reactive nitrogen compounds, is investigated in the joined project SCAVEX. The European project PARTEMIS focuses on the release of particulate emissions from aircraft engines. Besides lightning strokes of thunderstorms the air traffic is the only direct source of pollutants in the tropopause region.