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Differential Optical Absorption Spektoscopy (DOAS) Observations from HALO

Subject Area Atmospheric Science
Term from 2007 to 2017
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 47530744
 
Final Report Year 2017

Final Report Abstract

Within the present SPP-1294 phase projects, two state-of-the-art novel DOAS (Differential Optical Absorption Spectroscopy) instruments (namely the mini-DOAS and the 2-D Imaging DOAS instrument) were developed, certified, tested and successfully deployed on the HALO aircraft, and in the case of the 2-D imaging instrument due to missing flight opportunities on HALO on some other aircrafts. The mini-DOAS instrument participated in the TACTS/ESMVal in August 2012, Narval in December 2013/January 2014, ML-Cirrus in March/April 2014, Acridicon in Sept./Oct. 2014, OMO in July/August 2015, and Polstracc/GW-LCYCLE/SALSA in Dec 2015/March 2016, and the 2-D imaging instrument in missions in spring 2011 at Mt. Enta, Italy, autumn 2011 Indiana, USA and 2012 during BROMEX in Barrow, Alaska, USA. Moreover, significant progress has been made within the present project to develop suitable retrieval methods, tools and software to infer absolute concentration from the remotely sensed quantities (i.e. mostly slant column amounts of the targeted species) from the air-borne UV/vis/nearIR limb measurements under all skies. These include (a) a versatile radiative transfer Monte Carlo model (McArtim) with which Jacobian (and Hesse) matrices can be calculated, (b) a novel Mie scattering code (GDT-matrix) with which the light scattering of irregular shaped solid small particle (c.f. cirrus ice particle) can be calculated to high accuracy, (c) an inversion code (Mars) for non-linear inversions based on the optimal estimation, and (d) a novel method for the retrieval of absolute concentrations at flight level from limb measurements. Important scientific achievements were also obtained using the novel 2-D Imaging DOAS instrument HAIDI. During its deployment around Mt Etna in 2011, spatially resolved measurements of SO2, BrO and for the first time of OClO in volcanic plumes were mapped in 2D. The inferred maps contributed significantly to the quantitative understanding of the BrO formation and destruction in volcanic plumes. Also for the first time, the significance of reactive chlorine species in plume photochemical processes was demonstrated. The potential of the 2D Imaging DOAS for NO2 air pollution monitoring and estimation of total emission strength was demonstrated during measurements in a research campaign around Indianapolis (Indiana, USA, 2011). Further, the HAIDI instrument contributed to the so far most comprehensive study on the bromine explosion mechanism in the Arctic preformed within the framework of BRomine, Ozone, and Mercury EXperiment (BROMEX) campaign at Barrow (Alaska, USA) in spring 2012. The campaigned focussed on mechanism to explain the release of active bromine from fresh sea ice. Specifically, the observations performed with the HAIDI instrument provided evidence for the release of reactive bromine from the snow covered inland surfaces. The mapping of BrO concentrations with HAIDI over a large area of fresh sea ice with frost flowers, as well as with snow of potentially high salinity, lead to a better understanding of the sources of bromine radicals in the Arctic. Also the relevance of NO2 for the amount of BrO in the lower troposphere was demonstrated. Correlations of BrO with aerosols and altitude gained new insight into the bromine transport and the bromine recycling mechanism.

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