Synonyms: 
Atmospheric Tomography Mission
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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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Meteorological Measurement System

The Meteorological Measurement System (MMS) is a state-of-the-art instrument for measuring accurate, high resolution in situ airborne state parameters (pressure, temperature, turbulence index, and the 3-dimensional wind vector). These key measurements enable our understanding of atmospheric dynamics, chemistry and microphysical processes. The MMS is used to investigate atmospheric mesoscale (gravity and mountain lee waves) and microscale (turbulence) phenomena. An accurate characterization of the turbulence phenomenon is important for the understanding of dynamic processes in the atmosphere, such as the behavior of buoyant plumes within cirrus clouds, diffusions of chemical species within wake vortices generated by jet aircraft, and microphysical processes in breaking gravity waves. Accurate temperature and pressure data are needed to evaluate chemical reaction rates as well as to determine accurate mixing ratios. Accurate wind field data establish a detailed relationship with the various constituents and the measured wind also verifies numerical models used to evaluate air mass origin. Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.

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Diode Laser Hygrometer

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ACTIVATE (Falcon); FIREX-AQ, ATom, KORUS-AQ, and SEAC4RS (DC-8); POSIDON (WB-57); CARAFE (Sherpa); CAMP2Ex and DISCOVER-AQ (P-3); and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated spectral lines near 1.4 μm and is comprised of a compact laser transceiver and a sheet of high grade retroflecting road sign material to form the optical path. Optical sampling geometry is aircraft-dependent, as each DLH instrument is custom-built to conform to aircraft geometric constraints. Using differential absorption detection techniques, H2O(v) is sensed along the external path negating any potential wall or inlet effects inherent in extractive sampling techniques. A laser power normalization scheme enables the sensor to accurately measure water vapor even when flying through clouds. An algorithm calculates H2O(v) concentration based on the differential absorption signal magnitude, ambient pressure, and temperature, and spectroscopic parameters found in the literature and/or measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators.

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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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Chemical Ionization Mass Spectrometer

The single mass analyzer CIMS (S-CIMS) was developed for use on NASA’s ER-2 aircraft. Its first measurements were made in 2000 (SOLVE). Subsequently, it has flown on the NASA DC-8 aircraft for INTEX-NA, DICE, TC4, and ARCTAS, as well as on the NCAR C-130 during MILAGRO/INTEX-B. HNO3 is measured by selective ion chemical ionization via the fluoride transfer reaction: CF3O- + HNO3 → HF • NO3- + CF2O In addition to its fast reaction rate with HNO3, CF3O- can be used to measure additional acids and nitrates as well as SO2 [Amelynck et al., 2000; Crounse et al., 2006; Huey et al., 1996]. We have further identified CF3O- chemistry as useful for the measurement of less acidic species via clustering reactions [Crounse et al., 2006; Paulot et al., 2009a; Paulot et al., 2009b; St. Clair et al., 2010]: CF3O- + HX → CF3O- • HX where, e.g., HX = HCN, H2O2, CH3OOH, CH3C(O)OOH (PAA) The mass analyzer of the S-CIMS instrument has recently been upgraded from a quadrupole to a time-of-flight (ToF) analyzer. The ToF admits the sample ion beam to the ion extractor, where a pulse of high voltage orthogonally deflects and accelerates the ions into the reflectron, which in turn redirects the ions toward the multichannel plate detector. Ions in the ToF follow a V-shaped, 43 cm path from extractor to detector, separating by mass as the smaller ions are accelerated to greater velocities by the high voltage pulse. The detector collects the ions as a function of time following each extractor pulse. The rapid-scan collection of the ToF guarantees a high temporal resolution (1 Hz or faster) and simultaneous data products from the S-CIMS instrument for all mass channels [Drewnick et al., 2005]. We have flown a tandem CIMS (TCIMS) instrument in addition to the SCIMS since INTEX-B (2006). The T-CIMS provides parent-daughter mass analysis, enabling measurement of compounds precluded from quantification by the S-CIMS due to mass interferences (e.g. MHP) or the presence of isobaric compounds (e.g. isoprene oxidation products) [Paulot et al., 2009b; St. Clair et al., 2010]. Calibrations of both CIMS instruments for HNO3 and organic acids are performed in flight using isotopically-labeled reagents evolved from a thermally-stabilized permeation tube oven [Washenfelder et al., 2003]. By using an isotopically labeled standard, the product ion signals are distinct from the natural analyte and calibration can be performed at any time without adversely affecting the ambient measurement. We also fly calibration standards for H2O2 (evolved from urea-hydrogen peroxide) and MHP (from a diffusion vial).

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Airborne Tropospheric Hydrogen Oxides Sensor

ATHOS uses laser-induced fluorescence (LIF) to measure OH and HO2 simultaneously. OH is both excited and detected with the A2Σ+ (v’=0) → X2π (v”=0) transition near 308 nm. HO2 is reacted with reagent NO to form OH and is then detected with LIF. The laser is tuned on and off the OH wavelength to determine the fluorescence and background signals. ATHOS can detect OH and HO2 in clear air and light clouds from Earth's surface to the lower stratosphere. The ambient air is slowed from the aircraft speed of 240 m/s to 8-40 m/s in an aerodynamic nacelle. It is then pulled by a vacuum pump through a small inlet, up a sampling tube, and into two low-pressure detection cells - the first for OH and the second for HO2. Detection occurs in each cell at the intersection of the airflow, the laser beam, and the detector field-of-view.

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