Temporal evolution of ClONO_2 observed with Improved Limb Atmospheric Spectrometer (ILAS) during Arctic late winter and early spring in 1997

摘要

The temporal evolution of the volume mixing ratio (VMR) of chlorine nitrate (ClONO_2) observed with the Improved Limb Atmospheric Spectrometer (ILAS) is described for the Arctic late winter and early spring of 1997. The temporal development of ClONO_2 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 ClONO_2 were also observed; some of these low values are attributable to denitrification or to occurrence of polar stratospheric clouds. After mid-March, when ClONO_2 reached peak values, ClONO_2 decreased and showed much less variability. Comparison of ClONO_2 with HCl observed by the Halogen Occultation Experiment/Upper Atmospheric Research Satellite (HALOE/UARS) suggests a conversion of ClONO_2 into HCl earlier at high altitudes than at lower altitudes. During the period a marked enhancement in NO_2 was observed with a reduction in ClONO_2 in the vortex, providing the first evidence from space of the NO_2 time evolution in conjunction with ClONO_2. Continuous measurements of ClONO_2 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.