Improved MAX-DOAS measurements and retrievals focused on the marine boundary layer

A ground-based MAX-DOAS system was updated and used in multiple campaigns focused on measurements of halogens (especially iodine monoxide) as well as NO2 and formaldehyde in the remote marine boundary layer. In addition, spectral effects of liquid water (absorption, VRS and Brillouin scattering) and their influences on the DOAS retrieval are analyzed. The impact of insufficiently removed liquid water structures as a potential error source for trace gas retrievals is demonstrated and correction spectra for existing water cross-sections were retrieved. In the visible spectral range, an improvement of the DOAS fit quality of the order of 10% was achieved by introducing the retrieved correction spectra.