Measurements of Bromine Monoxide and Iodine Monoxide in the Lower Stratosphere: Constraints on Total Inorganic Halogen Budgets and Chlorine Activation

Halogens have important direct and indirect effects on atmospheric chemistry e.g. ozone destruction, oxidative balance, mercury processing, particle seeding and growth. The monoxides of bromine and iodine (BrO and IO) are important constituents of inorganic halogens and additionally can activate chlorine through interhalogen reactions. These species were measured by the Airborne Multi AXis Differential Optical Absorption Spectroscopy (AMAX-DOAS) instrument during the CONvective TRansport of Active Species in the Tropics (CONTRAST) campaign. Here we examine two case studies – CONTRAST RF06 and RF15 – which sampled the tropical UTLS during a horizontal transect jet-crossing into the mid-latitude lower stratosphere. Our measurements include the first detection of IO in the lower stratosphere. We use a chemical box-model – constrained by measurements of BrO and IO as well as by AWAS, TOGA, and other measurements on the aircraft – to determine the total budgets of inorganic bromine and iodine. We examine the implications for ozone destruction both directly and through activation of chlorine, and we further investigate correlations of total Bry and Iy with air mass indicators such as CFC-11.