Reaction of Chlorine Nitrate with Hydrogen Chloride and Water at Antarctic Stratospheric Temperatures

• Published in: Science
• Main Authors: Tolbert, Margaret A., Rossi, Michel J., Malhotra, Ripudaman, Golden, David M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Association for the Advancement of Science (AAAS) 1987
• Subjects: Antarctic; The Antarctic; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1126/science.238.4831.1258; https://www.science.org/doi/pdf/10.1126/science.238.4831.1258

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO 2 ) with H 2 O and hydrogen chloride (HCl) on surfaces that simulate polar stratospheric clouds [ice and nitric acid (HNO 3 )—ice and sulfuric acid] are studied at temperatures relevant to the Antarctic stratosphere. The reaction of ClONO 2 on ice and certain mixtures of HNO 3 and ice proceeded readily. The sticking coefficient of ClONO 2 on ice of 0.009 ± 0.002 was observed. A reaction produced gas-phase hypochlorous acid (HOCl) and condensed-phase HNO 3 HOCl underwent a secondary reaction on ice producing dichlorine monoxide (Cl 2 O). In addition to the reaction with H 2 O, ClONO 2 reacted with HCl on ice to form gas-phase chlorine (Cl 2 ) and condensed-phase HNO 3. Essentially all of the HCl in the bulk of the ice can react with ClONO 2 on the ice surface. The gaseous products of the above reactions, HOCl, Cl 2 O, and Cl 2 , could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the formation of condensed-phase HNO 3 could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.