Nitrosyl and nitryl chloride formation in H2SO4/HNO3/H2O/HCl solutions at 200 K

Infrared spectroscopy has been used to measure the vapor pressure of chlori ne containing species generated from H2SO4/HNO3/H2O/HCl solutions at 200 K. The vapor pressure was observed to be a function of solution composition. Two solution compositions were investigated. One solution remained a liquid whereas the second solution was a mixed liquid and solid phase (an ice slu rry). The liquid solution had a composition of 64.6 wt.% H2SO4/4.8 wt.% HNO 3/30.1 wt.% H2O/0.5 wt.% HCl and produced only vapor phase HCl. The ice slu rry solution had a composition of 76.6 wt.% H2SO4/30 wt.% HNO3/20.1 wt.% H2 O/0.3 wt.% HCl and produced HCl, ClNO, and ClNO2 vapor phase components. Th e sulfuric acid, nitric acid, and water content of these solutions are repr esentative of those present in polar stratospheric clouds (PSCs), however t he HCl concentrations are much higher than present within these clouds. The partitioning of chlorine between vapor phase HCl (50%) and ClNO/ClNO2 (50% ) for the ice slurry solution suggests a possible mechanism of halogen acti vation within PSCs. A reaction mechanism to model the observed chemistry is proposed.