Seminar Ozean, Eis, Atmosphäre

Denitrification is the removal of reactive nitrogen from the polar stratosphere by sedimentation of HNO3 containing polar stratospheric cloud (PSC) particles. Denitrification plays a key role in the polar chlorine chemistry as it slows down chlorine deactivation and leads to prolonged ozone destruction and enhanced ozone loss. Recent studies have shown that denitrification is not treated adequately in chemical transport models and that its understanding is crucial for modelling ozone loss in the Arctic stratosphere. The detection of large (r=3-10 um) HNO3 containing PSC particles has been a great progress in this understanding, making denitrification to one of the most dynamic topics in stratospheric research.
Denitrification has been studied using measurements of stratospheric HNO3 and N2O by the Airborne SUbmillimeter Radiometer ASUR, operated on board the NASA research aircraft DC-8. Using ancillary measurements denitrification is derived between December 1999 and March 2000. A special focus is given on the processes of both diabatic decent and photolysis of HNO3 in polar spring as these processes also change the stratospheric HNO3 profile. Vortexwide denitrification is determined and its distribution inside the vortex is studied. The results are compared with denitrification derived from in-situ measurements from high-altitude aircraft, and with output of the SLIMCAT chemical transport model applying different denitrification schemes.
Eventually new possibilities for research on PSC formation and denitrification using ASUR HNO3 measurements will be presented.