COBRA (impact of COmbined iodine and Bromine Release on the Arctic atmosphere) is a UK IPY (International Polar Year) consortium that aims to investigate the release mechanisms of iodine in the Arctic and the potential combined effects of iodine and bromine on its atmosphere. The team measured reactive inorganic halogens (BrO, IO, OIO, I2), O3, Hg, HOx, HCHO, NOx, VOCs and reactive halocarbons from temporary laboratories located on the eastern shore of Hudson Bay, north of Kuujjuarapik, during February-March 2008. Met balloons and O3 sondes were launched daily. COBRA set up an ice camp and flux chamber experiments ~500 m into the bay to directly measure halogen emissions and ozone deposition, and measured physical, chemical and biological characteristics of the sea-ice (and potentially of frost flowers) at different depths. The project is linked with OOTI, which carried out a simultaneous field experiment at Kuujjuarapik.