UAS Chromatograph for Atmospheric Trace Species

The Unmanned Aircraft Systems (UAS) Chromatograph for Atmospheric Trace Species (UCATS) was designed and built for autonomous operation on remotely piloted aircraft, but has also been used on manned aircraft. It uses chromatography to separate atmospheric trace gases along narrow heated columns, followed by precise and accurate detection with electron capture detectors. There are currently three chromatography channels on UCATS, which measure nitrous oxide (N2O) and sulfur hexafluoride (SF6); CFC-11, CFC-12, CFC-113, and halon 1211; and chloroform (CHCl3) and carbon tetrachloride. On an earlier version of UCATS, with only two channels, we also measured methane, hydrogen, and carbon monoxide, along with N2O and SF6. In addition, there is a small ozone instrument and a tunable diode laser instrument for water vapor. Gas is pumped into the instruments from an inlet outside the aircraft, measured, and vented. UCATS has flown on the Altair UAS, the GV during HIPPO, the NASA Global Hawk UAS during the Global Hawk Pacific (GloPac) and ATTREX missions, where a record was set for the longest duration research flight (more than 28 hours), the DC-8 for ATom, and the ER-2 for DCOTSS. UCATS is relatively lightweight and compact, making it ideal for smaller platforms, but it is easily adaptable to a mid-size platform like the GV or Global Hawk. The data are used to measure sources and sinks of trace gases involved in climate and air quality, as well as transport through the atmosphere.

UCATS is three different instruments in one enclosure:

1. 3-channel (formerly 2-channel, up until 2020) gas chromatograph (GC)
2. Dual-beam ozone photometer (OZ)
3. Tunable diode laser (TDL) spectrometer for water vapor (WV)

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Altair, Global Hawk - AFRC, DC-8 - AFRC, Gulfstream V - NSF, WB-57 - JSC, ER-2 - AFRC
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PAN and Trace Hydrohalocarbon ExpeRiment

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

3 ECDs with packed columns (OV-101, Porapak-Q, molecular sieve).

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

2-channel MSD (mass selective detector). The MSD analyzes two independent samples air concentrated onto TE cooled Haysep traps, which are then heated to desorb the analytes and separate using 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 are 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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Airborne Chromatograph For Atmospheric Trace Species

ACATS-IV is a 4-channel gas chromatograph with electron capture detection (ECD) that measures a variety of halocarbons and other long-lived trace gases in the stratosphere. The instrument is currently configured to measure CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), halon-1211 (CBrClF2), chloroform (CHCl3), methane (CH4), and hydrogen (H2) every 125 s, and nitrous oxide (N2O) and sulfur hexafluoride (SF6) every 250 s. Each channel is comprised of a sample loop (2-10 cm3 volume), gas sampling valve (GSV), chromatographic column pair, ECD, electrometer, and several flow, temperature, and pressure controllers. In-flight calibration is carried out every 625 s (1250 s for N2O and SF6) by injecting a dried, whole air standard containing approximately 80% of tropospheric mixing ratios.

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