Proton-Transfer-Reaction Mass Spectrometer

PTR-MS is a state-of-the-art chemical ionization mass spectrometry technique that allows for fast (seconds) and highly sensitive (detection limits in the tens of pptv range) of volatile organic compounds (VOCs). A detailed description of the measurement principle and the instrument can be found at:

The technique was developed in the mid-1990s at the University of Innsbruck in Austria and has since then become a routine and integral part of most tropospheric chemistry field campaigns including INDOEX 1999, SOS 1999, TEXAQS 2000, AOE 2001, BEWA 2002, ECHO 2003, ARCTAS-2008, DISCOVER-AQ 2011 – just to name a few of the campaigns in which the University of Innsbruck measurement team has been involved. An interactive presentation of the airborne PTR-MS instrument can be found at: (click on interactive viewer and on PTR-MS)

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PAN and Trace Hydrohalocarbon ExpeRiment

PANTHER uses Electron Capture Detection and Gas Chromatography (ECD-GC) and Mass Selective Detection and Gas Chromatography (MSD-GC) to measure numerous trace gases, including Methyl halides, HCFCs, PAN, N20, SF6, CFC-12, CFC-11, Halon-1211, methyl chloroform, carbon tetrachloride.

3 ECD (electron capture detectors), packed columns (OV-101, Porpak-Q, molecular sieve).

1 ECD with a TE (thermal electric) cooled RTX-200 capillary column.

2-channel MSD (mass selective detector). The MSD analyses two independent samples concentrated onto TE cooled Haysep traps, then passed through two temperature programmed RTX-624 capillary columns.

With the exception of PAN, all channels of chromatography are normalized to a stable in-flight calibration gas references to NOAA scales. The PAN data is normalized to an in-flight PAN source of ≈ 100 ppt with ±5 % reproducibility. This source is generated by efficient photolytic conversion of NO in the presence of acetone. Detector non-linearity is taken out by lab calibrations for all molecules.

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PeroxyAcetylNitrate, Aldehydes and Ketones

The Ames PANAK instrument is a computerized 3- channel Capillary Gas Chromatographic system designed for the collection and analysis of low ppt (10-12 v/v) levels of peroxyacyl nitrates (PANs), alkyl nitrates, and tertrachloroethene in Channels 1 and 2; and C2-C3 aldehydes, C1-C2 alcohols, C3-C4 ketones, and C1-C2 nitriles in channel 3. Channels 1 and 2 use ECD detectors and have a sampling frequency of 2.5 minutes. Channel 3 uses a Photo Ionization detector placed in series with a Reduction Gas detector and has a sampling frequency of 5 minutes. The main manifold draws 5 SL/min of ambient air through a heated Teflon lined probe from which each of the three instrument channels draws a 200 ml aliquot of sample air. This aliquot is dried by passing it through a –35 °C cold trap, cooled to -140 °C for constituent pre concentration, and then heat desorbed into the gas chromatographic columns. All calibrations are performed in-flight by using an installed dilution system and in a manner that mimics ambient air sampling. Primary standards are generally referred to a series of permeation tubes. In addition high concentration standards are also carried on board. Sensitivities under typical conditions are: 1-3 ppt PANs, 1-5 ppt alkyl nitrates, 5-20 ppt OVOC, and 20-30 ppt nitriles.

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Charged-coupled device Actinic Flux Spectroradiometers

The Charged-coupled device Actinic Flux Spectroradiometers (CAFS) instruments measure in situ down- and up-welling radiation and combine to provide 4 pi steradian actinic flux density spectra from 280 to 650 nm. The sampling resolution is ~0.8 nm with a full width at half maximum (FWHM) of 1.7 nm at 297 nm. From the measured flux, photolysis frequencies are calculated for ~40 important atmospheric trace gases including O3, NO2, HCHO, HONO and NO3 using a modified version of the NCAR Tropospheric Ultraviolet and Visible (TUV) radiative transfer model. The absolute spectral sensitivity of the instruments is determined in the laboratory with 1000 W NIST-traceable tungsten-halogen lamps with a wavelength dependent uncertainty of 3–5%. During deployments, spectral sensitivity is assessed with secondary calibration lamps while wavelength assignment is tracked with Hg line sources and comparisons to spectral features in the extraterrestrial flux. The optical collectors are characterized for angular and azimuthal response and the effective planar receptor distance. CAFS have an excellent legacy of performance on the NASA DC-8 and WB-57 platforms during atmospheric chemistry and satellite validation mission. These include AVE Houston 2004 and 2005, PAVE, CR-AVE, TC4, ARCTAS, DC3, SEAC4RS, KORUS-AQ, ATom and FIREX-AQ. For FIREX-AQ, upgraded electronics and cooling reduced noise and allowed for a decrease to 1 Hz acquisition.

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Airborne Scanning Microwave Limb Sounder

The Airborne Scanning Microwave Limb Sounder (A-SMLS) makes wide-swath vertical profile observations of the composition
of the upper troposphere and lower stratosphere (the atmospheric region from ~10–20km altitude). A-SMLS measurements are
well suited to studies of convective outflow, long-range pollution transport, and exchange of air between the
troposphere and stratosphere. These atmospheric processes have strong impacts on climate and air quality but are
currently incompletely understood. Improved understanding of these issues is one of the main goals of NASA’s atmospheric
composition Earth science focus area. A-SMLS airborne observations reflect the priority spaceborne “Ozone and Trace Gas”
observables identified in the recent Decadal Survey.

A-SMLS was initially developed and flown on the WB-57 under the NASA Instrument Incubator Program (IIP), following
which, it was adapted to the ER-2 platform. Subsequent work, funded under an additional IIP, has upgraded the receivers
to ones that require cooling to only 70K rather than the previously needed 4K, and to use newer technology digital
spectrometers. Test flights for A-SMLS in this new configuration are planned, but further work, proposed here, is needed
to make the instrument fully “campaign ready”.

A-SMLS observes a ~300km-wide swath ~300km ahead of the aircraft in a 2D raster scan (azimuth and elevation), with
~10x10km horizontal sampling (across and along-track). As typically configured, A-SMLS measures water vapor, ozone, and
carbon monoxide. Retuning of the instrument (including in flight) can provide measurements of other species (including
N2O, HCN, CH3CN, H2CO, and others).

The instrument would be a particularly valuable addition to multi-aircraft campaigns. The broad swath A-SMLS
observations from the ER-2 could be used in near-real-time to help guide lower altitude aircraft carrying in situ
sensors to regions of interest.

As part of NASA's Airborne Instrument Technology Transition (AITT) program, the instrument is currently being updated to
help cement its suitability for campaign-mode operations, specifically, this involves:

- Addition of a liquid cooling loop to transfer waste heat from the existing ~70K cryocooler to the outer skin of the
ER-2 wing pod.

- Development of an “intelligent scan” system that accounts for aircraft orientation etc. when performing the 2D
raster limb scan on the atmosphere.

- Completion of a thorough ground-based instrument calibration.

- Development of an on-board radiance compression scheme that will enable key data to be transferred to the ground for
use in real-time flight planning as described above.

- Updates to the analysis algorithms software used for Aura MLS, enabling their application to A-SMLS observations.

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WB-57 - JSC (no longer fits), ER-2 - AFRC
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