Flying shadow

Shadow of a BO-105 helicopter of RV Polarstern wandering over ice floes in the mariginal sea ice region of the Southern Ocean. The helicopter is carrying an airborne DOAS (Differential Optical Absorption Spectroscopy) remote sensing instrument measuring the vertical distribution of bromine monoxide (BrO) in the atmosphere. Despite mixing ratios in the order of only a few parts per trillion, BrO dramatically changes the chemistry of the boundary layer over areas of many square kilometers during springtime in Polar regions. It can completely deplete tropospheric ozone or oxidize gaseous elemental mercury leading to its deposition to the biosphere.