Laboratory studies of sticking coefficients and heterogeneous reactions important in the Antarctic stratosphere

Abstract

Laboratory studies of sticking coefficients of H 2 O, HCl, Cl 2 and HNO 3 on ice and heterogeneous reactions of ClONO 2 with ice or HCl/ice have been performed in a fast flow reactor. A quadrupole mass spectrometer with electron impact ionization was used as a detector. Measured sticking coefficients are: 0.3 (+0.7. −0.1) for H 2 O, 0.4 (+0.6, −0.2) for HCl, <1.0 × 10 −4 for Cl 2 , and 0.3 (+0.7, −0.1) for HNO 3 at 200 K. The reaction probability of ClONO 2 on ice was found to be 0.06 (±0.03) while HOCl was observed as a sole product in the gas phase. With HCl present in ice, the reaction probability of ClONO 2 is greatly enhanced, approaching 0.27 (+0.73, −0.13) while molecular chlorine was found to be the major product in the gas phase. Another reaction product was nitric acid which remained in the solid phase. Since the polar stratospheric clouds contain ice particles or possibly HCl/ice particles on the surface, the present results should be a major factor in producing the observed springtime ozone depletion in the Antarctic stratosphere.