Dynamics and chemistry of tropospheric bromine explosion events in the Antarctic coastal region

[1] We investigate chemistry and dynamics of bromine explosion events during Antarctic spring of 1999 and 2000 using ground-based differential optical absorption spectroscopy (DOAS) observations of BrO, surface ozone, and ozone sounding measurements performed at the German research station Neumayer, located at the coast of the Antarctic continent (70°39′S, 8°15′W). BrO maps from the GOME satellite instrument show huge areas of elevated BrO above the sea ice around Antarctica, covering several thousand square kilometers. Although the Neumayer station is located at a distance of only 7 km to the coast, bromine-activated air masses are only detected by our ground-based DOAS instrument under particular meteorological conditions. We use trajectory calculations in high temporal and spatial resolution in combination with sea ice maps to determine the source of air masses arriving at Neumayer. A comparison of these model calculations with measurements is in very good agreement with the theory that reactive bromine is heterogeneously released by sea-salt surfaces: in the majority of cases, enhanced levels of BrO are observed whenever a part of the probed air masses was previously in contact with sea ice surfaces, while depletion of surface ozone occurs only if the air at ground comes from the ice covered ocean. After being uplifted by advection processes, bromine-activated and ozone-depleted air masses are sometimes observed at high altitudes (>4000 m). This vertical transport of reactive bromine may have an impact on the free tropospheric ozone budget and on local climate in the Antarctic coastal region during springtime. BrO enhancements are usually accompanied by strong increases in light path (as detected by O4) owing to multiple scattering on aerosols, supporting the assumption that sea-salt particles, on which BrO recycling can take place, are present at the observation site.