NOAA Iodide Ion Time-of-Flight Chemical Ionization Mass Spectrometer

Iodide Ion ToF (Time-of-Flight) CIMS (Chemical Ionization Mass Spectrometer)

Principle of the Measurement

Chemical ionization mass spectrometric detection of gas phase organic and inorganic analytes via I- adduct formation

Species Measured

Reactive nitrogen species: HNO3 (nitric acid), HONO (nitrous acid), HO2NO2 (peroxynitric acid), N2O5 (dinitrogen pentoxide), HNCO (isocyanic acid) 
Halogen Species: ClNO2, HCl, HBr, HOBr, HOCl, Cl2, Br2 
Low to intermediate volatility organic species

Time Response

Instrumental response <1 sec, Field response is limited by inlet surface affinity for a particular species

Detection Limit

Precision on 1s data various by species


(15% + 1 pptv) for N2O5
(20% + 1 pptv) for ClNO2
(30% + 15 pptv) for HONO
(25% + 10 pptv) for HO2NO2
(15% + 15 pptv) for HNO3
(20% + 5 pptv) for HNCO
(20% + 15 pptv) for HCOOH
(30% + 1 pptv) for halogenated species


TOFWERK/Aerodyne Research Inc. (modified)

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Reactive Nitrogen

Instrument: Reactive Nitrogen

Principal Investigator: David W. Fahey

NOAA Aeronomy Laboratory
325 Broadway,R/E/AL6
Boulder, CO 80303

Principle of Operation:
The instrument is designed to measure nitric oxide (NO) and the sum of reactive nitrogen oxides (NOy). Species included in NOy are NO, NO2, HNO3, N2O5 and ClONO2. NO is measured by detecting light from the chemiluminescent reaction between reagent ozone and NO in the ambient sample. NOy is reduced to NO by catalytic reduction on a gold surface with carbon monoxide (CO) acting as a reducing agent. The catalyst is located outside the aircraft fuselage in order to avoid inlet line losses. Two reaction vessels are incorporated in the instrument to allow for simultaneous measurement of NO and NOy. Ca1ibration with NO or NO2 is made by standard addition several times during a flight. The baseline of each measurement is determined in part by the addition of synthetic air that contains no reactive nitrogen. The difference between the sample flow velocity in the inlet opening and the aircraft velocity cause aerosol particles in the atmosphere to be oversampled. For sizes below 5 micrometers in diameter, this feature assists in the identification of aerosol particles that contain NOy.



Accuracy: < 20% plus precision
Detection limit: < 0.1 ppbv NOy, ~0.02 ppbv NO
Response time: 1 sec
Location on the ER2: Lower Q-bay rack

Reference: D.W. Fahey et al., In situ aerosol measurements of total reactive nitrogen, total water, and aerosol in a polar stratospheric cloud in the Antarctic, J. Geophys. Res. 94 11-99-11315, 1959.

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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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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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