Due to dynamically variable meteorological conditions, springtime Arctic O3 levels exhibit significant interannual variability in the lower stratosphere. The polar vortex that formed in winter 2011 was strong and cold for an unusually long time. Eureka, Nunavut, located on Ellesmere Island (80.05ºN, 86.42ºW), was mostly inside the vortex from October 2010 until late March 2011. The Bruker 125HR Fourier transform infrared spectrometer installed at the Polar Environment Atmospheric Research Laboratory at Eureka acquired measurements from February 23 to April 6 during the Canadian Arctic Atmospheric Chemistry Experiment Validation Campaign. These measurements showed unusually low O3, HCl, and HNO3 total columns compared to the previous 14 years. After the dynamical effects were removed, the values of the O3, HCl, and HNO3 total columns were smaller than those from previous years, and confirmed the chlorine activation and chemical ozone depletion. To quantify the chemical ozone loss, the Single-Layer Isentropic Model of Chemistry and Transport (SLIMCAT) model and the passive subtraction method was used. The chemical ozone depletion was calculated as the mean percentage difference between the measured O3 and the SLIMCAT passive O3, and was found to be 35%.