Microwave measurements of arctic chlorine monoxide and computed chemical ozone loss in spring 2000

The University of Bremen (Germany) operates a microwave radiometer for the detection of stratospheric chlorine monoxide at 204 GHz, ozone at 142 GHz and water vapor at 22 GHz. The radiometer for atmospheric measurements (RAM) is located at the primary Arctic station of the Network for the Detection of Stratospheric Change - NDSC - in Ny-Ålesund, Spitsbergen at 79° North and 12° East. We observed a maximum chlorine monoxide (ClO) volume mixing ratio (VMR) of 1.2 ± 0.2 ppb in early March 2000 inside the polar vortex. The observed ClO decreased almost linearly to background values until late March. The vortex averaged chemical ozone loss derived from our observations accumulated to 45% at the 475 K isentropic level over the complete vortex existence period from December 1999 to March 2000.