Synonyms: 
HOOH
Hydrogen peroxide

Peroxide Chemical Ionization Mass Spectrometer

The measurement of gas phase peroxide species, H2O2 and CH3OOH, contribute to our scientific understanding of the photochemistry of trace gases and particles prior to and after their transport and processing through deep convective clouds. The PCIMS instrument used to make these measurements in the DC3/SEAC4RS mission is new and this will be its first use in an airborne science campaign.

The PCIMS instrument is a slightly modified CIMS instrument manufactured by THS Instruments LLC. Mechanically it consists of a differentially pumped quadrupole mass spectrometer. The instrument operates in negative ion mode and currently I- and O2- reagent ions are used to measure hydrogen peroxide and methylhydroperoxide, respectively, by the formation of cluster ions at masses 80 and 161. The reagent ions are produced by flowing a N2/CH3I/O2 mixture past a 210Po foil.

On the G-V, the PCIMS inlet system starts with a PFA Teflon lined heated G-V HIMIL inlet. From the HIMIL the inlet line is comprised of PFA Teflon and is also heated (Hot-Tube, Clayborn Lab). Analytical blanks are performed by diverting the ambient sample flow through a trap filled with Carulite 200 catalyst. Gas phase calibrations are performed through standard additions to ambient air. H2O2 is added from a urea hydrogen peroxide solid decomposition source or by the evaporation of a nano-fluidic flow of a dilute aqueous solution. CH3OOH is added by the evaporation of a nano-fluidic flow of a dilute aqueous solution. The ambient, calibration and reagent gases are vented overboard through the G-V common exhaust.

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NSF G-V
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URI Peroxides and Formaldehyde Instrument

POPS measures CH2O, H2O2, and CH3OOH.

CH2O is measured by aqueous collection followed by enzyme fluorescence detection.

H2O2 and CH3OOH is measured by aqueous collection followed by HPLC separation and enzyme fluorescence detection.

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JPL Mark IV Balloon Interferometer

The MkIV interferometer operates in solar absorption mode, meaning that direct sunlight is spectrally analyzed and the amount of various gases at different heights in the Earth's atmosphere is derived from the shapes and depths of their absorption lines. The optical design of the MkIV interferometer is based largely on that of the ATMOS instrument, which has flown four times on the Space Shuttle. The first three mirrors in the optical path comprise the suntracker. Two of these mirrors are servo-controlled in order to compensate for any angular motion of the observation platform. The subsequent wedged KBr plates, flats, and cube-corner retro-reflectors comprise a double-passed Michelson interferometer, whose function is to impart a wavelength-dependent modulation to the solar beam. This is achieved by sliding one of the retro-reflectors at a uniform velocity so that the recombining beams interfere with each other. A paraboloid then focusses the solar beam onto infrared detectors, which measure the interferometrically modulated solar signal. Finally, Fourier transformation of the recorded detector outputs yields the solar spectrum. An important advantage of the MkIV Interferometer is that by employing a dichroic to feed two detectors in parallel, a HgCdTe photoconductor for the low frequencies (650-1850 cm-1) and a InSb photodiode for the high frequencies (1850-5650 cm-1), the entire mid-infrared region can be observed simultaneously with good linearity and signal-to-noise ratio. In this region over 30 different gases have identifiable spectral signatures including H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HNO4, N2O5, H2O2, ClNO3, HOCl, HCl, HF, COF2, CF4, SF6, CF2ClCFCl2, CHF2Cl, CF2Cl2, CFCl3, CCl4, CH3Cl, C2H2, C2H6, OCS, HCN, N2, O2, CO2 and many isotopic variants. The last three named gases, having well known atmospheric abundances, are important in establishing the observation geometry of each spectrum, which otherwise can be a major source of uncertainty. Similarly, from analysis of T-sensitive CO2 lines, the temperature profile can be accurately determined. The simultaneity of the observations of all these gases greatly simplifies the interpretation of the results, which are used for testing computer models of atmospheric transport and chemistry, validation of satellite data, and trend determination.

Although the MkIV can measure gas column abundances at any time during the day, the highest sensitivity to atmospheric trace gases is obtained by observing sunrise or sunset from a balloon. The very long (~ 400 km) atmospheric paths traversed by incoming rays in this observation geometry also make this so-called solar occultation technique insensitive to local contamination.

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Balloon, DC-8 - AFRC
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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 Scanning Microwave Limb Sounder

The National Research Council decadal survey for earth science identified the need for a Global Atmospheric Composition Mission (GACM) to address crucial issues on how changes in atmospheric composition affect the quality and well-being of life on earth. The baseline GACM instrument suite comprises UV/Vis and IR/SWIR spectrometers and an advanced microwave limb sounder working together to retrieve atmospheric composition worldwide with high spatial resolution. The Scanning Microwave Limb Sounder (SMLS) is designed to meet the measurement requirements of GACM by providing complete orbit-to-orbit retrieval of O3, N2O, temperature, water vapor, CO, HNO3, ClO, and volcanic SO2 in the upper troposphere and lower stratosphere. Unlike previous MLS instruments that only scanned the limb vertically leaving large orbit to orbit gaps, SMLS will simultaneously scan both in azimuth and elevation providing complete global coverage with 6 or more repeat measurements per day. SMLS will employ extremely sensitive, broadband, sideband-separating, SIS receivers centered at 230 and 640 GHz that provide the same precision as those on Aura MLS with a 100 fold reduction in integration time. SMLS will use a novel antenna design that provides high vertical resolution and enables rapid horizontal scanning of the field of view.

Since the late summer 2008, the development of the SMLS instrument technology has been underway within NASA Earth Science Technology Office’s Instrument Incubator Program. The objective of this development is to advance the core signal path technologies required for a microwave limb sounder with the capability to map the composition of the upper troposphere and stratosphere with 50x50x1 km spatial sampling and six times daily mid-latitude repeat coverage. The specific goals of this effort include:

* the mitigation of the optics and calibration risks of the SMLS flight sensor design by constructing and testing an airborne prototype of the SMLS sensor and calibration system - A-SMLS - using prototype sideband-separating mixers, line sources, and advanced spectrometers and calibration targets;

* the mitigation of the development risks of the cryogenics system by developing a flight-like cryostat and demonstrating an end-to-end prototype of the SMLS signal path from the antenna interface through the back-end electronics, and quantifying its stability, calibration accuracy, linearity, and sensitivity; and

* the demonstration of the potential science measurement capability of SMLS through the A-SMLS science flights.

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