We present profile measurements of key constituents relevant to stratospheric chemistry and dynamics such as ozone (O3), nitrous oxide (N2O), and chlorine monoxide (ClO) taken during the 2002--03 northern hemisphere winter by the Odin Sub-Millimetre Radiometer (SMR), a limb-sounding satellite sensor launched in February 2001. The observations of the chemically passive tracer N2O show a subsidence of lower stratospheric air masses inside the Arctic vortex in the range of 3--5 km, or 60--100 K in terms of potential temperature, for the period November 2002 to March 2003. Activated chlorine in the form of ClO was observed inside the vortex from the beginning of December until mid-February. The accumulated chemical ozone loss over this period, derived from the correlation of ozone with N2O, is estimated to be 28 ¿ 9% on the 50 ppbv level of N2O, i.e., for lower stratospheric air masses subsiding from ~23 down to 19 km, the lower limit of the Odin/SMR ozone measurement in the 501.8 GHz band.