In both polar regions tropospheric ozone regularly decreases during springtime to negligible concentrations in the atmospheric boundary layer. Here we report the observation of a dramatic ozone depletion event in the atmospheric boundary layer in the vicinity of frost flower fields in the marginal ice zone of the Arctic Ocean monitored by instrumentation on board of the icebreaker RV Polarstern. The ozone mixing ratio decreased from approximately 40 to below 1 ppbV in less than 7 hours. The analyses of backward trajectories and the synoptical conditions demonstrate that the observed decrease was not caused by the transport of ozone-free air, but that the ozone depletion occurred locally. Accordingly, bromine oxide, which is formed during the photochemical destruction of ozone in the presence of reactive bromine compounds, was significantly enhanced: bromine oxide concentrations of approximately 1 · 109 molecules cm-3 are retrieved around the same location from satellite observations. The release of bromine on or, as a result of, the presence of frost flowers appears to be the most likely explanation for the activation of reactive bromine compounds and subsequent depletion of ozone. We conclude that areas in the polar regions covered with frost flowers are the sources of the bromine leading to tropospheric ozone depletion episodes and the observed clouds of bromine oxide.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > POL1-Processes and interactions in the polar climate system