Universität Bremen Measurements of halogen oxides by scattered sunlight differential optical absorption spectroscopy Hilke Oetjen January 2009 Measurements of halogen oxides by scattered sunlight differential optical absorption spectroscopy Fachbereich für Physik und Elektrotechnik der Universität Bremen zur Erlangung des akademischen Grades eines Doktor der Naturwissenschaften (Dr. rer. nat.) von Hilke Oetjen aus Rotenburg (Wümme) Gutachter 1. Prof. John P. Burrows 2. Prof. Otto Schrems Eingereicht am: 27. Januar 2009 Mündliche Prüfung am: 1. Dezember 2009 2 Abstract This work describes measurements of the tropospheric halogen species iodine mon-oxide (IO) and bromine monoxide (BrO) with multi-axis differential optical absorption spectroscopy (MAX-DOAS) at various locations: Svalbard (79°N), Andøya (69°N), List (55°N), Crete (35°N), and Maldives (5°N). Furthermore, the radiative transfer model SCIATRAN was used to investigate the sensitivity of the MAX-DOAS tech-nique towards tropospheric absorbers as well as to estimate concentrations of IO and upper limits only for BrO. IO was detected at Svalbard, List, and Maldives with con-centrations of 0.4 ppt, 2.2 ppt, and 2.8 ppt, respectively, but was below the average detection limits of 0.6 ppt and 1.3 ppt for Andøya and Crete, respectively. Uncertain-ties are estimated to be in the range of 2-3 ppt.