Measurements of reactive trace gases in the marine boundary layer using novel DOAS methods

Reactive Halogen Species (RHS) can have a large impact on tropospheric chemistry. Already small concentrations in the marine boundary layer (MBL) can have a significant impact on the global budget of ozone and other trace-gases. Shipborne measurements of BrO and IO were conducted in the MBL from 70°S to 90°N to obtain a global picture of their distribution over several years. A focus were upwelling regions, which can provide large amounts of precursor substances for RHS in the MBL, of which some were measured simultaneously by project partners. Measurements in the tropical Atlantic showed BrO concentrations below 2 ppt in agreement with previous observations. IO was detected with concentrations of up to 1 ppt, its distribution was found to correlate with surface water iodide concentrations. In the Peruvian upwelling region MAX-DOAS and CE-DOAS measurements showed agreeing surface VMR of up to 1.4 ppt. The MAX-DOAS retrieval agreed with previous satellite observations of IO in this region. For polar measurements, background concentrations of IO of 0.2-0.4 ppt during the respective summer period were observed. An additional source of reactive bromine in the MBL was observed for the first time from the ground: Polar air-masses were observed south of the Azores yielding BrO concentrations of 4-6 ppt. Glyoxal was not found in the remote MBL of the tropical Atlantic and Pacific above a detection limit of 35 ppt. Relative water vapour absorption band strengths in the wavelength interval from 400-480 nm were analysed systematically and correction factors from 0.5-2 were found, leading to improvements of the spectral retrieval. Vibrational Raman scattering of N2 and O2 was quantified for the first time in MAX-DOAS measurements, yielding a reduction of up to 30% of IO measurement error