CH4

The NASA Goddard Greenhouse Gas suite measures CO₂, CH₄ and water vapor using two commercial analyzers (Los Gatos Research) modified for airborne operation. The principle of detection is infrared laser absorption spectroscopy combined with a multi-pass gas cell that gives an effective absorption path length of several kilometers and measurement precisions of < 0.5%. Both instruments are coupled to a central data acquisition system and are essentially autonomous.

The GHG package is also uniquely capable of directly measuring surface emission and uptake using the eddy covariance technique. This includes fluxes of CO2, CH4, and sensitble and latent heat.

Carbon dioxide (CO₂) and methane (CH₄) are potent greenhouse gases and the foremost drivers of man-made climate change. Fossil fuel combustion is the primary source of CO₂, while CH₄ is released during natural gas extraction (fracking), enteric fermentation (cow burps), and other anthropogenic and natural processes. Measurements of these gases help us to quantify and compare the strength of different sources and thus build more accurate emission inventories. They can also serve as tracers for source attribution of other trace species.

Targeting Fourier Transform Spectrometer (FTS) measuring infrared spectra from 4.5 to 13.4 µm. AES was the airborne testbed for the EOS/Aura TES instrument and operated ~1994-2000.

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.

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.

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.