The novel HALO mini-DOAS instrument was developed for measurements of UV/vis/near-IR spectra of scattered
skylight in limb and nadir geometry aboard the new research aircraft HALO. The absorptions of a suite
of trace gases (O3, O4, NO2, CH2O, BrO, OClO, and others) are identified in the measured spectra using the
DOAS-technique. Previously employed methods to infer absolute concentrations from DOAS measurements
rely on a priori knowledge of aerosols and cloud cover. The recently developed scaling method promises to enable
the retrieval of target gas concentrations under all sky conditions. Effective light path lengths are estimated
by employing a scaling gas, whose concentration at flight level is known, in conjunction with modelled profile
shapes, radiative transfer calculations, and using the measured absorptions of the targeted species relative
to those of the scaling gas. The present thesis describes the development and characterises the measurement
properties of the HALO mini-DOAS instrument. For the first time, random and systematic errors of the scaling
method are thoroughly investigated. It is argued that random errors are 10 – 20% for most measurement conditions
and that the scaling method is practically unperturbed by changing cloud cover if applied appropriately.
It is however shown that biases may occur if the assumed profile shapes are significantly different from actual
profile shapes. Retrieved mixing ratios of BrO and NO2 from measurements obtained during the science mission
TACTS/ESMVal in August/September 2012 indicate that (a) no enhanced tropospheric BrO was detected
in the mid-troposphere (3.5 – 9 km altitude) near the Antarctic continent (65° S) in spring (Sept. 13, 2012), (b)
LMS and bottom polar vortex [BrO] agree with previous measurements, (c) other oxidants beside O3 influence
NO oxidation in the UT/LS where [N2O] < 310 ppb, and (d) the same finding was confirmed for very low-NOx
conditions, although the latter measurements are uncertain