A41A-0005
LIF instrument for airborne measurements of OH, HO2 and RO2 radicals in the upper troposphere

Thursday, 17 December 2015
Poster Hall (Moscone South)
Sebastian Broch1, Christopher Künstler2, Mathias Bachner2, Knut Dahlhoff3, Frank Holland2, Norbert Bayer3, Hendrik Fuchs2, Andreas Hofzumahaus2, Peter Jansen3, Jörg Wolters3, Martin Zöger4 and Andreas Wahner2, (1)Forschungszentrum Jülich GmbH, Jülich 52428, Germany, (2)Forschungszentrum Jülich, Institute of Energy and Climate Research, IEK-8: Troposphere, Jülich, Germany, (3)Forschungszentrum Jülich, Central Institute for Engineering, Electronics and Analytics, ZEA-1, Jülich, Germany, (4)German Aerospace Center (DLR), Mess- und Sensortechnik, Oberpfaffenhofen, Germany
Abstract:
We present the development and first deployment of a new instrument for the measurement of OH, HO2 and RO2 radicals in the upper troposphere aboard the German research aircraft HALO (High Altitude and LOng range). The instrument is based on the well-established laser induced fluorescence (LIF) technique (Holland et al., 2003; Fuchs et al., 2008). It has two separate measurement cells, one for the direct detection of OH (OH channel) and one for alternating measurements of HO2 and RO2 radicals (ROx channel) after chemical conversion to OH by the reaction with NO.

For its deployment on HALO, a Gulfstream-V aircraft, a special air inlet for the OH channel was developed and built at Forschungszentrum Jülich. It is based on the shrouded-inlet design by Eisele et al. (1995) and allows for a controlled reduction of the air flow velocity prior to sampling as well as the performance of inflight calibrations. There is no special inlet system for the ROx channel. It samples directly from the fast airflow along the aircraft. In contrast to our ground based instrument, longer inlet tubes are required to bring the ambient air into the detection cells inside the aircraft. The inflight calibration unit of the OH inlet allows for monitoring relative changes of the OH detection sensitivity with height. Ambient water vapor is photolysed at 185 nm upstream of the inlet nozzle to produce an additional OH signal which can be evaluated by using measurements of water vapor mixing ratio, lamp intensity, and airflow velocity. Due to the very small water vapor mixing ratios in the UTLS region this technique is limited to altitudes up to 11 km.

We will give an overview of the technical concept and instrumental setup for the application on HALO. We will show results from laboratory characterization measurements concerning the radical detection sensitivities and first results from flights performed during the OMO-Asia campaign in summer 2015.

Literature:

Holland et al., J. Geophys. Res., 108, 8246, 2003

Fuchs et al., Rev. Sci. Instrum., 79, 084104, 2008

Eisele et al., J. Geophys. Res., 102, 27993, 1997

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