The TIBAGS project addresses the study of iodine monoxide (IO) and its relations in the atmosphere. IO is a reactive halogen compound formed via oxidation of iodine atoms by ozone. Apart from destroying tropospheric ozone, iodine impacts on atmospheric composition by changing the oxidative capacity and by the formation of fine atmospheric particles which may grow to cloud condensation nuclei.

IO has so far mostly been observed in the marine boundary layer and at Polar sites by local ground-based instruments. Its main sources are thought to be natural biogenic emissions by algae and phytoplankton but the knowledge on iodine sources and chemistry is still incomplete.

IO amounts are close to the detection limit of state-of-the-art satellite sensors; however, observation of IO from space is possible. In this project, investigations of IO are carried out using measurements from the SCIAMACHY (SCanning Imaging Absorption Spectrometer for Atmospheric CartograpHY) instrument on Envisat. Atmospheric IO amounts are deduced using absorption spectroscopy in the visible spectral range and appropriate radiative transfer calculations. IO is observed, e.g. above Antarctica, where widespread enhanced IO columns appear in spring time with interesting temporal and spatial variation.

This project shall contribute to the understanding of the role of reactive iodine and its connection to relevant parameters of the biosphere and atmosphere. Regions of interest are mainly the Polar Regions, selected mid-latitude coastlines and productive open ocean areas. Starting from the existing data set, the time series of satellite data will be extended further and analysed in more detail. Investigations of spatial patterns and temporal variations shall help to characterize source regions of iodine species. Activities include comparisons of IO distributions with bromine monoxide and short-lived organic compounds in the troposphere as well as with biological conditions in the oceans and sea ice cover in Polar Regions.