Emissions of chlorine compounds into the atmosphere by anthropogenic activities destroy the stratospheric ozone layer, thereby monitoring the concentration of these compounds becomes necessary in order to investigate any observed evolution, and to verify compliance with different international protocols banning their production by human processes.

Many of these chlorine species show strong spectral feautures at submillimeter wavelengths and can therefore be measured using microwave remote sensing techniques. The instrument used for this study is the Airborne Submillimeter Radiometer ASUR. It measures thermal emission lines of a variety of atmospheric trace gases related to chlorine chemistry in the stratosphere e.g HCl- the chlorine reservoir gas, ClO- which is very efficient for catalytic ozone destruction in the lower stratosphere during winter, N2O - the chemically inert trace gas suitable to differentiate between chemical and dynamical processes, and ozone among others. The spectral range of ASUR is between 604.3 and 662.3 GHz. By using a non-linear least squares inversion technique, volume mixing ratio profiles can be retrieved from the spectrally resolved pressure broadened lines.

This talk will focus on chlorine activation in the arctic winters over the past years by evaluating the time series from 1995 to 2003. Evidence of a large chemical ozone losses and a strong, spatially variable chlorine activation with high ClO and low HCl mixing ratios will be presented.