Shield Melts Off
Introduction
Over the past three decades, global warming has heated up the Arctic more than any other place on earth. It has now been found that Arctic warming and the resulting sea ice melt could be changing the chemistry of the Arctic atmosphere. Reactions that happen between the sunlit snow that sits atop the Arctic sea ice and the air above it produce bromine, a halogen gas derived from sea salt. This bromine purges pollutants from the atmosphere and destroy surface-level ozone. This ozone is toxic unlike the protective ozone layer higher up in the atmosphere.
Source
Down To Earth, May 2013