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Abstract

This thesis provides analysis results of an extensive data set of stratospheric trace gases(NO2, BrO, OClO) derived from ground based zenith sky DOAS measurements (1996 — 2016) at Kiruna, Sweden. Kiruna (67.84°N, 21.41°E) is located north of the polar circle and is thus well suited for the investigation of polar stratospheric ozone chemistry. The analysed trace gases are involved in the key-chemical reactions controlling stratospheric ozone. Thus their long-term monitoring is important for the independent control of the international CFC emission reduction agreements and to predict the future evolution of the ozone layer. The Kiruna zenith sky DOAS measurements are one of the longest records at polar regions and thus very well suited for these tasks. The thesis has three major parts. First, the whole set of raw spectra was re-analysed with consistent retrieval settings taking into account the most recent advances of the passive DOAS technique. The retrieval settings were further optimised by various sensitivity tests. Second, the derived data products were compared to several independent measurements, where overall very good agreement was found. Finally the long term data set was used to investigate the temporal variations on various scales and to relate them to stratospheric meteorological parameters. In particular the long term trends of NO2 and BrO were determined. For NO2 it was found that the amount has not significantly changed (a slight positive, but non-significant change of about 1.5 ± 2%/decade was found.). This is in good agreement with the trend of its precursor gas N2O (2.3%/decade). For BrO a strong positive trend before 2001 and a negative trend after 2005 is found confirming the expected reduction of the emissions of the precursor gases. Here it should be noted that the results of this thesis extend the existing time records by several years. From the measured BrO amounts the total stratospheric bromine mixing ratio was estimated to about 20.7 ppt, and the contribution of very short lived bromine species to about 5 ppt.