The temporal evolution of the volume mixing ratio (VMR) of chlorine nitrate (ClONO2) observed with the Improved Limb Atmospheric Spectrometer (ILAS) is described for the Arctic late winter and early spring of 1997. The temporal development of ClONO2 on the 475‐K isentropic surface during winter and spring is characterized by high variability in the VMR with seasonal enhancement to about 2 ppbv. In February, depleted values of ClONO2 were also observed; some of these low values are attributable to denitrification or to occurrence of polar stratospheric clouds. After mid‐March, when ClONO2 reached peak values, ClONO2 decreased and showed much less variability. Comparison of ClONO2 with HCl observed by the Halogen Occultation Experiment/Upper Atmospheric Research Satellite (HALOE/UARS) suggests a conversion of ClONO2 into HCl earlier at high altitudes than at lower altitudes. During the period a marked enhancement in NO2 was observed with a reduction in ClONO2 in the vortex, providing the first evidence from space of the NO2 time evolution in conjunction with ClONO2. Continuous measurements of ClONO2 through winter and spring over the Arctic are limited to date. The ILAS measurements reported in this paper will be useful for reanalyzing the seasonal variation of chlorine activation/deactivation processes in the Arctic lower stratosphere that control the degree of ozone destruction.