The details of the spatial and temporal patterns of IO in comparison to BrO are not well understood yet. However, the observed differences in the distributions suggest that the two halogen oxides are released by different processes. While the BrO is produced by inorganic emissions and the bromine explosion cycle, it is an open question whether the majority of IO is of biological origin. The cold Antarctic waters show high biological activity, and cold water diatoms may produce organic iodine species. Considerable differences between the South and North Polar regions might be linked to the fact that the biospheres are distinct and are emitting iodine compounds in different amounts and speciation.
3.3 The Stratospheric Ozone Layer
As early as the second half of the 20th century, the stratosphere was seen as fragile to human perturbation. Public interest grew even more with the detection of the Antarctic ozone hole in the mid-1980’s. Until the mid-1990s, a steady decrease of up to 3-6% per decade in the ozone abundance has been observed over the South Pole, North Pole and the mid-latitudes. The most striking feature is the massive loss of stratospheric ozone over Antarctica every southern spring. This ozone loss is so large because very low stratospheric temperatures over Antarctica in wintertime foster the underlying depletion processes. The polar vortex isolates the air during the polar night and allows the cold conditions to remain stable and Polar Stratospheric Clouds (PSC) to grow. In this environment the chemistry of ozone depletion begins with the conversion of reservoir species to chemically active molecules on the surface of the PSC. These react with ozone in catalytical reaction cycles resulting in the effective destruction of the O3 molecules. In addition, ozone loss was also observed in the tropics and mid-latitudes. Today, there is broad agreement that a continuous monitoring of stratospheric ozone, the ozone hole and of those species impacting the ozone chemistry is necessary in order to detect possible signs of recovery, and to find out how far the cooling of the stratosphere and the strengthening of the Brewer-Dobson circulation as a consequence of climate change will delay or accelerate the recovery of the ozone layer (Rex et al. 2006, Newman et al. 2007).
SCIAMACHY allows exploitation of new opportunities using the limb backscatter, as well as solar or lunar occultation measurement modes, to determine PSC and vertically resolved concentration profiles of trace gases in the stratosphere, in addition to the established column measurements from the nadir mode.