The scaling method applied to HALO measurements: Inferring absolute trace gas concentrations from airborne limb spectroscopy under all sky conditions
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 spe...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
2017
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| Online Access: | https://archiv.ub.uni-heidelberg.de/volltextserver/22573/ https://archiv.ub.uni-heidelberg.de/volltextserver/22573/1/Diss_Hueneke_digital.pdf https://doi.org/10.11588/heidok.00022573 https://nbn-resolving.org/urn:nbn:de:bsz:16-heidok-225732 |
| Summary: | 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. |
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