The tropopause seperates troposphere and stratosphere. The tropopause region is a region of very high climate sensitivity, due to the strong gradients in radiatively important trace gases and temperature. Relativly small changes in the chemical composition can have large impact on radiative forcing and thus on climate, also at the ground.

Through our observations of a wide range of halocarbons and related trace gases using the GhOST-MS instrument onboard the research aircraft HALO we contribute to a better understanding of chemical budgets and transport processes in the tropopause region. Transport is investigated through mean age, while the chemistry aspects are related to the bromine and chlorine budget, with an emphasis on short lived sources of chlorine and bromine top the stratosphere. These chemical active species also give information on the time scales of transport through the tropopause as a function of distance to the tropopause, as the chemical breakdown interacts with transport.