HALO instrumentation

Instrument type: Chemiluminescence detector
Measured species: Total reactive nitrogen (NO_y)
Mission participation: (TBA)
Instrument PI: DLR-PA

The AENEAS (AtmosphEric Nitrogen oxides mEAsuring System) instrument measures total reactive nitrogen. Total reactive nitrogen (NO_y) is the sum of all reactive nitrogen species in the atmosphere, namely NO, NO₂, HNO₃, PAN, HNO₂, HNO₄, N₂O₅, ClONO₂, and others. The detection of total reactive nitrogen is based on a well-established technique, comprising catalytic conversion and chemiluminescence.

References:
> Ziereis, H. et al., (2022): Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016, Atmos. Chem. Phys., 22, 3631–3654, doi:10.5194/acp-22-3631-2022.

Instrument type: Mass spectrometer
Measured species: H₂O   or   HCl, HNO₃, SO₂ and HONO
Mission participation: (TBA)
Instrument PI: DLR-PA

AIMS uses SF₅⁻ reagent ions for the simultaneous measurement of trace gas concentrations of HCl, HNO₃ and SO₂ in the  pptv to ppmv (10⁻¹² to 10⁻⁶ mol mol⁻¹) range with in-flight and online calibration (AIMS-TG). In the AIMS-H2O configuration, air is directed through the gas discharge region where ion–molecule reactions lead to the production of hydronium ion clusters, H₃O⁺(H₂O)_n (n = 0, 1, 2), in a complex reaction scheme similar to the reactions in the D-region of the ionosphere. These ions are counted to quantify the ambient water vapor mixing ratio.

References:
> Kaufmann et al., (2016): The airborne mass spectrometer AIMS – Part 1: AIMS-H₂O for UTLS water vapor measurements, Atmos. Meas. Tech., 9, 939–953, doi:10.5194/amt-9-939-2016.
> Jurkat et al., (2016): The airborne mass spectrometer AIMS – Part 2: Measurements of trace gases with stratospheric or tropospheric origin in the UTLS, Atmos. Meas. Tech., 9, 1907–1923, doi:10.5194/amt-9-1907-2016. 

Instrument type: Off-Axis-Integrated-Cavity-Output-Spectroscopy (ICOS)
Measured species: OCS, CO₂, CO, CH₄and H₂O (tropospheric)
Mission participation: (TBA)
Instrument PI: FZ Jülich 

This spectrometer carries out high resolution carbonyl sulfide (OCS) measurements during aircraft campaigns to improve our understanding of the contribution of OCS to the stratospheric aerosol layer. It uses the Off-Axis-Integrated-Cavity-Output-Spectroscopy (ICOS) measurement technique to determine OCS, CO₂, CO, CH₄ and tropospheric H₂O.

Link to instrument webpage:
https://www.fz-juelich.de/en/ice/ice-4/research/synergetic-use-of-instruments-and-models/halo

References:
> Kloss, C.  et al., (2021), Airborne Mid-Infrared Cavity enhanced Absorption spectrometer (AMICA), Atmos. Meas. Tech., 14, 5271–5297, doi:10.5194/amt-14-5271-2021

Instrument type: Laser absorption spectrometer
Measured species: CO, CH₄, N₂O
Mission participation: t.b.a.
Instrument PI: MPI-Chemie, Mainz

ATTILA is a custom-built two-cell mid-infrared room-temperature quantum cascade laser absorption spectrometer. It is equipped with two room-temperature quantum cascade lasers that measure CO, CH₄, and N₂O in a two-cell system.

References:
> Ort, L., et al., (2024): In-flight characterization of a compact airborne quantum cascade laser absorption spectrometer, Atmos. Meas. Tech., 17, 3553–3565, doi: 10.5194/amt-17-3553-2024.

Instrument type: Chemiluminescence detector
Measured species: Ozone (O₃)
Mission participation: (TBA)
Instrument PI: KIT

FAIRO’s sensitivity is ~9000 counts s⁻¹ per ppbv of ozone. Its precision is entirely determined by the number of photons reaching the detector (being a photomultiplier), i.e. is quantum-noise limited. The relative precision (ΔO₃/O₃ in %) thus follows Poisson statistics and scales with the square root of the measurement frequency f and with the inverse O₃ mixing ratio: ΔO₃/O₃ ∝ f^0.5 · O₃^−0.5. At typical O₃ mixing ratios between 10 and 100 ppbv (and 1 bar), the precision is 0.3–1.0% at f = 10 Hz. The maximum measurement frequency is 50 Hz.

References:
> Zahn A. et al., (2012): A fast and precise chemiluminescence ozone detector for eddy flux and airborne application, Atmos. Meas. Tech., 5, 363–375, doi:10.5194/amt-5-363-2012.

Instrument type: Lyman-α hygrometer
Measured species: total/gas-phase H2O
Mission participation: (TBA)
Instrument PI: FZ Jülich 

The Lyman-α hygrometer FISH (Fast In-situ Stratospheric Hygrometer) is one of the most advanced and sensitive in-situ instruments world-wide for mea- suring water vapor in the UTLS. This climate-sensitive region has the lowest water vapor concentrations, making it a particular challenge for measuring in- struments. For almost three decades the instrument was flown on many different research aircraft and places around the world and measured water vapor and the ice water content of cirrus clouds.

Link to instrument webpage:
https://www.fz-juelich.de/en/ice/ice-4/research/synergetic-use-of-instruments-and-models/halo
https://www.fz-juelich.de/de/ice/ice-4/ueber-uns/wissinfra/fish

References:
> Meyer et al., (2015), Two decades of water vapor measurements with the FISH fluorescence hygrometer: a review, Atmos. Chem. Phys., 15, 8521–8538, doi:10.5194/acp-15-8521-2015.
> Zöger et al., (1999), Fast in situ stratospheric hygrometers: A new family of balloon-borne and airborne Lyman α photofragment fluorescence hygrometers. J. Geophys. Res., doi: 10.1029/1998JD100025.

Instrument type: in situ gas chromatography and mass spectrometry
Measured species: short-lived brominated source gases: CH₂Br₂, CHBr₃, CH₂ClBr, CHCl₂Br and CHClBr₂
Mission participation: (TBA)
Instrument PI: GU Frankfurt

GhOST-MS is a two-channel GC instrument. An electron capture detector (ECD) is used in an isothermal channel to measure SF₆ and CFC-12 with a time resolution of 1 min. The second channel is temperature programmed and uses a cryogenic pre-concentration system  and a mass spectrometer (MS) for detection. It measures halocarbons in the chemical ionization mode with a time resolution of 4 min.

References:
> Keber, T. et al., (2020): Bromine from short-lived source gases in the extratropical northern hemispheric upper troposphere and lower stratosphere (UTLS), Atmos. Chem. Phys., 20, 4105–4132, doi:10.5194/acp-20-4105-2020.

Instrument type: Gas chropatograph and mass spectrometer
Measured species: CH₂Cl₂, CHCl₃, CH₃Cl, CFC-11, CFC-113, HFC-125, HFC-134a, and iso- and n-pentane
Mission participation: (TBA)
Instrument PI: University of Wuppertal

HAGAR-V comprises a two-channel gas chromatograph (GC) with electron capture detection (ECD) as well as a non-dispersive infrared absorption module for the detection of CO₂. It additionally comprises a mass spectrometer (MS) coupled to two GC channels which can thus be used either for the detection of a wide range of atmospheric trace gases (different target species on each channel) or to double the measurement frequency (same target species on both channels). 

References:
> Lauther, V. et al., (2022): In situ observations of CH₂Cl₂ and CHCl₃ show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon, Atmos. Chem. Phys., 22, 2049–2077, doi:10.5194/acp-22-2049-2022.
> Lauther, V.: Airborne in situ measurements of short-lived chlorocarbons and investigation of their pathways from northern hemispheric source regions into the lowermost stratosphere, PhD thesis, Bergische Universität Wuppertal, doi:10.25926/KQVQ-HB36, 2020.
> Werner, A. et al., (2010): Quantifying transport into the Arctic lowermost stratosphere, Atmos. Chem. Phys., 10, 11623–11639, doi:10.5194/acp-10-11623-2010.

Instrument type: multi-phase water sensor
Measured species: water vapour and condensed water (simultaneously)
Mission participation: (tba)
Instrument PI: PTB Darmstadt

HAI is based on a special variant of TDLAS (Tunable Diode Laser Absorption Spectroscopy) which is self-calibrating. A robust, open and aerodynamic measuring cell located outside the aircraft body directly measures the gaseous water vapour content of the air flowing through it. Another two-channel measuring unit is located inside the aircraft, at the end of a heated sample collection tube where two sensors working independently of each other measure the total water content of the sample.

Link to instrument webpage:
Click to read information on HAI in a press release by PTB

References:
> Buchholz, B., et al., (2017): HAI, a new airborne, absolute, twin dual-channel, multi-phase TDLAS-hygrometer: background, design, setup, and first flight data, Atmos. Meas. Tech., 10, 35–57, doi: 10.5194/amt-10-35-2017.

Instrument type: Chemical ionisation mass spectrometry
Measured species: PAN, PAA
Mission participation: t.b.a.
Instrument PI: MPI-Chemie, Mainz

Chemical ionisation mass spectrometry (CIMS) uses I⁻ (the iodide anion) as a primary reactant ion to measure NO₃ and N₂O₅.

Link to instrument webpage:
https://www.mpic.de/3562041/methods

References:
> Dörich, R., Eger, P., Lelieveld, J., and Crowley, J. N., (2021): Iodide CIMS and m∕z 62: the detection of HNO3 as NO3− in the presence of PAN, peroxyacetic acid and ozone, Atmos. Meas. Tech., 14, 5319–5332, doi: 10.5194/amt-14-5319-2021.
> Eger, P. G., et al., (2019): Chemical ionization quadrupole mass spectrometer with an electrical discharge ion source for atmospheric trace gas measurement, Atmos. Meas. Tech., 12, 1935-1954, doi: 10.5194/amt-12-1935-2019.

(Image: HALO-CIMS instrument; https://www.mpic.de/3562041/methods  || Credit: MPI-C)

Instrument type: proton-transfer-reaction mass spectrometry (PTR-MS)
Measured species: VOCs
Mission participation: t.b.a.
Instrument PI: KIT, Karlsruhe

An ion source produces hydronium (H₃O⁺) reagent ions which react with trace gases in the sample air within a drift tube (reaction chamber). Proton transfer takes place if the proton affinity of the target VOC is higher than that of H₂O. VOCH⁺ and reagent ions are analysed in a quadrupole mass spectrometer (QMS) or via time-of-flight measurements (ToF).

References:
> Förster, E., et al., 2023: Chemical and dynamical identification of emission outflows during the HALO campaign EMeRGe in Europe and Asia, Atmos. Chem. Phys., 23, 1893–1918, doi: 10.5194/acp-23-1893-2023.

Instrument type: Laser-induced fluorescence (LIF)
Measured species: HO_X
Mission participation: t.b.a.
Instrument PI: MPI-C, Mainz

This is the first airborne LIF-FAGE instrument measuring HO_x with a dedicated inlet preinjector (IPI) system installed for the purpose of removing atmospheric OH, enabling real-time measurements and quantification of potential chemical background OH interferences, OH−CHEM. HORUS measures an off-resonance signal to discern the net OH fluorescence signal.

References:
> Marno, D., et al., (2021): Calibration of an airborne HO_x instrument using the All Pressure Altitude-based Calibrator for HO_x Experimentation (APACHE), Atmos. Meas. Tech., 13, 2711–2731, doi: 10.5194/amt-13-2711-2020.
> Martinez, M., et al., (2010):: Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: airborne measurements, Atmos. Chem. Phys., 10, 3759–3773, doi: 10.5194/acp-10-3759-2010.

Instrument type: automated flask sampler
Measured species: CO₂, CH₄, N₂O, H₂, SF₆
Mission participation: t.b.a.
Instrument PI: MPI-BGC, Jena

The device is equipped with 12 slots for holding 1 L glass flasks with automatically operated valves at both ends. Sample air, collected outside the aircraft fuselage with a dedicated inlet, flows into a drying unit filled with magnesium perchlorate, and a pump is used to flush and pressurise the flasks, up to approximately 1500 hPa. Flasks are collected after flight and analysed in a lab.

References:
> Gałkowski, M., et al., (2021): In situ observations of greenhouse gases over Europe during the CoMet 1.0 campaign aboard the HALO aircraft, Atmos. Meas. Tech., 14, 1525–1544, doi: 10.5194/amt-14-1525-2021.

Instrument type: wavelength-scanning cavity ring-down spectroscopy (CRDS)
Measured species:CO₂, CO, CH₄
Mission participation: t.b.a.
Instrument PI: MPI-BGC, Jena

The core method of the measurement is wavelength-scanning cavity ring-down spectroscopy (CRDS), whereby an infrared-wavelength laser light is injected into a high-finesse optical cavity. First, the strength of the incident laser beam gradually increases over time and thus increases the detector’s sensitivity. After reaching the designated signal level, the laser is turned off. The time constant of the resulting exponential decay (ring-down time) depends on the absorption coefficient of the measured compound for the laser wavelength, tuned so that the scan along selected individual spectral lines of the measured molecules is possible.

References:
> Gałkowski, M., et al., (2021): In situ observations of greenhouse gases over Europe during the CoMet 1.0 campaign aboard the HALO aircraft, Atmos. Meas. Tech., 14, 1525–1544, doi: 10.5194/amt-14-1525-2021.
> Chen, H., et al., (2010): High-accuracy continuous airborne measurements of greenhouse gases (CO₂ and CH₄) using the cavity ring-down spectroscopy (CRDS) technique, Atmos. Meas. Tech., 3, 375–386, doi: 10.5194/amt-3-375-2010.

Instrument type: Chemoluminescence detector
Measured species: NO, NO₂
Mission participation: t.b.a.
Instrument PI: MPI-Chemie, Mainz

Measurements are made by exciting NO₂ with a laser. The fluorescence resulting from NO de-excitation is detected by a photomultiplier tube as a signal which is approximately proportional to the ambient NO₂ mixing ratio.

References:
> Tadic, I., et al., (2020): Net ozone production and its relationship to nitrogen oxides and volatile organic compounds in the marine boundary layer around the Arabian Peninsula, Atmos. Chem. Phys., 20, 6769–6787, doi: 10.5194/acp-20-6769-2020.
> Nussbaumer, C. M., et al., (2023): Measurement report: Airborne measurements of NO_x fluxes over Los Angeles during the RECAP-CA 2021 campaign, Atmos. Chem. Phys., 23, 13015–13028, doi: 10.5194/acp-23-13015-2023.

Instrument type: absorption spectrometry
Measured species: RO₂
Mission participation: t.b.a.
Instrument PI: Bremen University

PeRCEAS combines the peroxy radical chemical amplification (PeRCA) and cavity ring-down spectroscopy (CRDS) techniques in a dual-channel instrument.

References:
> George, M., et al., (2023): Airborne observations of peroxy radicals during the EMeRGe campaign in Europe, Atmos. Chem. Phys., 23, 7799–7822, doi: 10.5194/acp-23-7799-2023.
> George, M., et al., (2020): Airborne measurement of peroxy radicals using chemical amplification coupled with cavity ring-down spectroscopy: the PeRCEAS instrument, Atmos. Meas. Tech., 13, 2577–2600, doi: 10.5194/amt-13-2577-2020.

Instrument type: gas chromatography-mass spectrometer (GC-MS)
Measured species: VOCs
Mission participation: t.b.a.
Instrument PI: MPI-C, Mainz

The system incorporates a novel  cryogen-conservative VOC enrichment system that is based on  the differential pressure between a  LN2 dewar and the trap housing to  transport the cryogen as a liquid, and  rapidly cool the traps to the desired  temperatures. 

References:
> Bourtsoukidis, E., et al., (2017): An aircraft gas chromatograph–mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow, Atmos. Meas. Tech., 10, 5089–5105, doi: 10.5194/amt-10-5089-2017.

Instrument type: Chemical ionisation mass spectrometry
Measured species: Total peroxides, H2O2, CO, HCHO, CH4
Mission participation: t.b.a.
Instrument PI: MPI-Chemie, Mainz

Measurements are obtained using a modified commercial instrument  called HYPHOP (hydrogen peroxide and higher organic peroxide monitor) together with the infrared laser absorption instrument TRISTAR (tracer in situ TDLAS for atmospheric research).

References:
> Hottmann, B., et al., (2020): Impact of the South Asian monsoon outflow on atmospheric hydroperoxides in the upper troposphere, Atmos. Chem. Phys., 20, 12655–12673,  doi: 10.5194/acp-20-12655-2020.
> HYPHOP: Hamryszczak, Z. et al., (2023): HYPHOP: a tool for high-altitude, long-range monitoring of hydrogen peroxide and higher organic peroxides in the atmosphere, Atmos. Meas. Tech., 16, 4741–4756, doi: 10.5194/amt-16-4741-2023.

> TRISTAR: Tomsche, L., et al., (2019): Upper tropospheric CH₄ and CO affected by the South Asian summer monsoon during the Oxidation Mechanism Observations mission, Atmos. Chem. Phys., 19, 1915–1939, doi: 10.5194/acp-19-1915-2019.

Instrument type: Quantum Cascade Laser based spectrometer
Measured species: N₂O, CO
Mission participation: WISE (2017), PHILEAS (2023), ASCCI (2025), NAWDIC (2026)
Instrument PI: JGU Mainz

UMAQS is based on the “Aerodyne Research Inc.“  Quantum Cascade Laser Mini Monitor which uses an astigmatic multi path Herriot cell with an optical pathlength of 76m. This instrument applies the direct absorption spectroscopy. 

Link to instrument webpage:
https://www.blogs.uni-mainz.de/fb08-ipa-en/messinstrumenteaghoor/

References:
Müller, S. et al., (2015): In situ detection of stratosphere-troposphere exchange of cirrus particles in the midlatitudes, Geophys. Res. Lett. 42: 949–955. doi: 10.1002/2014GL062556. 
> Kunkel, D. et al., (2019): Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves, Atmos. Chem. Phys., 19, 12607–12630, doi:10.5194/acp-19-12607-2019. 

(Image: UMAQS instrument; https://www.blogs.uni-mainz.de/fb08-ipa-en/messinstrumenteaghoor/  || Credit: Mainz University)

Instrument type: Laser hygrometer
Measured species: Total atmospheric water content (TWC)
Mission participation: t.b.a.
Instrument PI: DLR-PA

This instrument derives the concentration of water vapour in the sample flow by using the absorption of the 1.37 µm line from an indium–gallium–arsenide (InGaAs) tunable diode laser (TDL) in a closed measurement cell with a modified stainless-steel inlet line. The measurement range is 50–10000 ppmv, with a precision of 5 % or 50 ppmv, whichever is greater. Values are sampled at a frequency of 0.3–0.4 Hz.

References:
> Marsing, A., et al., (2023): Investigating the radiative effect of Arctic cirrus measured in situ during the winter 2015–2016, Atmos. Chem. Phys., 23, 587–609, doi: 10.5194/acp-23-587-2023.

…