The polar atmosphere in spring exhibits very unusual chemistry involving halogens like bromine and iodine. Bromine is probably released from brine on sea-ice, and iodine from algae on the underside of sea-ice. Once in the atmosphere these compounds cause very rapid destruction of ozone, and the oxidation of atomic mercury. This chemistry involves catalytic cycles which are fed by the hydroxide (OH) and hydroperoxy (HO2) radicals. Oxidised mercury then deposits on the snow, runs off into sea-water and enters the food chain. High levels of this toxic element occur in the indigenous inhabitants of the Arctic countries.

A number of UK, Irish and Canadian Institutes and Universities were involved in the project, including the Universities of Leeds, Manchester and York, the British Antarctic Survey (BAS), University College Cork (UCC), Canadian Meteorology Service, among others.

We travelled to Northern Quebec, Canada to the Whapmagoostui-Kuujjuaraapik Research Station (55° 17' N, 77° 46' W) on the east of Hudson Bay in February and March.