Synonyms: 
Methane
Column CH4

G2301-m

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G2301-f

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ARC Picarro

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NOAA Picarro

The Picarro G2401m is a commerical instrument that measures CO2, CH4, CO, and H2O. The analyzer is based on Wavelength-Scanned Cavity Ring Down Spectroscopy (WS-CRDS), a time-based measurement utilizing a near-infrared laser to measure a spectral signature of the molecule. Gas is circulated in an optical measurement cavity with an effective path length of up to 20 kilometers. A patented, high-precision wavelength monitor makes certain that only the spectral feature of interest is being monitored, greatly reducing the analyzer’s sensitivity to interfering gas species, and enabling ultra-trace gas concentration measurements even if there are other gases present. As a result, the analyzer maintains high linearity, precision, and accuracy over changing environmental conditions with minimal calibration required.

The measurement software of the NOAA Picarro has been modified to have a shorter measurement interval (~1.2 seconds instead of ~2.4 seconds) by reducing the number of scans of the CO spectroscopic peak and therefore yielding a less-precise CO measurement (1σ on 1-2 second measurements is ~9 ppb instead of ~4 ppb). The instrument was also modified to have a lower cell pressure set point (80 torr instead of 140 torr) to allow it to operate across the full pressure altitude range of the DC8 without requiring upstream pressurization of the sample stream.

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Harvard Tracer Suite

HTS is composed of two instruments based on absorption of near-infrared laser radiation in high finesse optical cavities. A Picarro G2401-m analyzer based on wavelength-scanned cavity ring-down spectroscopy (CRDS) measures CO2, CH4, and CO concentrations at 2-second intervals. A Los Gatos 913-0014 EP analyzer based on off-axis integrated cavity output spectroscopy (ICOS) measures N2O and CO concentrations at 1-second intervals. Extensive modifications have been applied to these commercial analyzers for flight and include vibration isolation, temperature control, additional flow control and pumping capacity for high-altitude sampling, sample drying, and in-flight calibrations using WMO-traceable compressed gas standards to verify stable and accurate performance throughout the full DC-8 flight envelope.

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Programmable Flask Package Whole Air Sampler

The PFP whole air sampler provides a means of automated or manual filling of glass flasks, twelve per PFP. The sampler is designed to remove excess water vapor from the sampled air and compress it without contamination into ~1-liter volumes. These flasks are analyzed at the NOAA’s Global Monitoring Division laboratory for trace gasses and at  the INSTAR’s Staple Isotope Lab laboratory for isotopes of methane. More than 60 trace gases found in the global atmosphere can be measured at mole fractions that range from parts-per-million (10-6), e.g., carbon dioxide, down to parts-per-quadrillion (10-15), e.g., HFC-365mfc.  The chemical species monitored include N2O, SF6, H2, CS2, OCS, CO2, CH4, CO, CFCs, HCFCs, HFCs, Solvents, Methyl Halides, Hydrocarbons and Perfluorocarbons.

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Harvard University Picarro Cavity Ring Down Spectrometer

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Picarro G1301-c Methane/Carbon Dioxide Analyzer

The Picarro CO2/CH4 Flight Analyzer is a real time, trace gas monitor capable of measuring these gases with parts-per-billion (ppbv) sensitivity onboard aircraft with varying cabin pressure and environmental conditions. The analyzer is based on Wavelength-Scanned Cavity Ring Down Spectroscopy (WS-CRDS), a time-based measurement utilizing a near-infrared laser to measure a spectral signature of the molecule. Gas is circulated in an optical measurement cavity with an effective path length of up to 20 kilometers. A patented, high-precision wavelength monitor makes certain that only the spectral feature of interest is being monitored, greatly reducing the analyzer’s sensitivity to interfering gas species, and enabling ultra-trace gas concentration measurements even if there are other gases present. As a result, the analyzer maintains high linearity, precision, and accuracy over changing environmental conditions with minimal calibration required.

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NSF G-V
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Advanced Whole Air Sampler

90 samples/flight
–7 x 10 sample + 1 x 8 sample + 2 x 6 sample modules

New canisters/valves/manifold design/control system

Fill times
–14 km 30 – 40 sec
–16 km 40 – 50 sec
–18 km 50 – 60 sec
–20 km 100 – 120 sec (estimated)

Analysis in UM lab: GC/MS; GC/FID; GC/ECD; GC/RGD

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Quantum Cascade Laser System

The Harvard QCLS (DUAL and CO2) instrument package contains 2 separate optical assemblies and calibration systems, and a common data system and power supply. The two systems are mounted in a single standard HIAPER rack, and are described separately below:

The Harvard QCL DUAL instrument simultaneously measures CO, CH4, and N2O concentrations in situ using two thermoelectrically cooled pulsed-quantum cascade lasers (QCL) light sources, a multiple pass absorption cell, and two liquid nitrogen-cooled solid-state detectors. These components are mounted on a temperature-stabilized, vibrationally isolated optical bench with heated cover. The sample air is preconditioned using a Nafion drier (to remove water vapor), and is reduced in pressure to 60 mbar using a Teflon diaphragm pump. The trace gas mixing ratios of air flowing through the multiple pass absorption cell are determined by measuring absorption from their infrared transition lines at 4.59 microns for CO and 7.87 microns for CH4 and N2O using molecular line parameters from the HITRAN data base. In-flight calibrations are performed by replacing the air sample with reference gas every 10 minutes, with a low-span and a high-span gas every 20 minutes. A prototype of this instrument was flown on the NOAA P3 in the summer of 2004.

The Harvard QCL CO2 instrument measures CO2 concentrations in situ using a thermoelectrically cooled pulsed-quantum cascade laser (QCL) light source, gas cells, and liquid nitrogen cooled solid-state detectors. These components are stabilized along the detection axis, vibrationally isolated, and housed in a temperature-controlled pressure vessel. Sample air enters a rear-facing inlet, is preconditioned using a Nafion drier (to remove water vapor), then is reduced in pressure to 60 mbar using a Teflon diaphragm pump. A second water trap, using dry ice, reduces the sample air dewpoint to less than –70C prior to detection. The CO2 mixing ratio of air flowing through the sample gas cell is determined by measuring absorption from a single infrared transition line at 4.32 microns relative to a reference gas of known concentration. In-flight calibrations are performed by replacing the air sample with reference gas every 10 minutes, and with a low-span and a high-span gas every 20 minutes.

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