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Synonyms: 
ARCTAS I
ARCTAS-CARB
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UNH Mercury

The UNHMERC instrument provides detailed information on atmospheric mercury. Measurements of total gaseous mercury (TGM) and gaseous elemental mercury (Hg°) are performed simultaneously with one minute time resolution using a custom four-channel atomic fluorescence spectrometer. The relative amount of reactive gaseous mercury (RGM = HgCl2 + HgBr2+ HgOBr + …) will be assessed through careful examination of the difference between TGM and Hg°. TGM is defined as the sum Hg° + RGM. Targeted aerosol sampling will also be conducted for particulate-phase mercury (HgP).

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Trace Organic Gas Analyzer

TOGA measures volatile organic compounds (VOCs). Specific data will be obtained for radical precursors, tracers of anthropogenic and biogenic activities, tracers of urban and biomass combustion emissions, products of oxidative processing, precursors to aerosol formation, and compounds important for aerosol modification and transformation. TOGA measures a wide range of VOCs with high sensitivity (ppt or lower), frequency (2.0 min.), accuracy (15% or better), and precision (<3%). Over 50 species are routinely measured (see PDF for full table) throughout the full DC-8 altitude range. TOGA is contained in a standard DC-8 rack, weighs less than 200 kg and consumes ~1 kW of power. The major components of the instrument are the inlet, cryogenic preconcentrator, gas chromatograph, mass spectrometer detector, zero air/calibration system, and the control/data acquisition system. All processes and data acquisition are computer controlled.

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DC-8 - AFRC, Gulfstream V - NSF
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Thermal-Dissociation Laser Induced Fluorescence

The UC Berkeley thermal-dissociation laser-induced fluorescence (TD- LIF) instrument detects NO2 directly and detects total peroxynitrates (ΣPNs ≡ PAN + PPN +N2O5 + HNO4. . .), total alkyl- and other thermally stable organic nitrates (ΣANs), and HNO3 following thermal dissociation of these NOy species to NO2. The sensitivity for NO2 at 1 Hz is 30 pptv (S/N=2) with a slope uncertainty of 5%. The uncertainties for the dissociated species are 10% for ΣPNs and 15% for ΣANs and HNO3.

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Proton-Transfer-Reaction Mass Spectrometer

PTR-MS is a state-of-the-art chemical ionization mass spectrometry technique that allows for fast (seconds) and highly sensitive (detection limits in the tens of pptv range) of volatile organic compounds (VOCs). A detailed description of the measurement principle and the instrument can be found at: http://en.wikipedia.org/wiki/Proton-transfer-reaction_mass_spectrometry

The technique was developed in the mid-1990s at the University of Innsbruck in Austria and has since then become a routine and integral part of most tropospheric chemistry field campaigns including INDOEX 1999, SOS 1999, TEXAQS 2000, AOE 2001, BEWA 2002, ECHO 2003, ARCTAS-2008, DISCOVER-AQ 2011 – just to name a few of the campaigns in which the University of Innsbruck measurement team has been involved. An interactive presentation of the airborne PTR-MS instrument can be found at: http://discover-aq.larc.nasa.gov/instruments.php (click on interactive viewer and on PTR-MS)

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NCAR NOxyO3

The NCAR NOxyO3 instrument is a 4-channel chemiluminescence instrument for the measurement of NO, NO2, NOy, and O3. NOx (NO and NO2) is critical to fast chemical processes controlling radical chemistry and O3 production. Total reactive nitrogen (NOy = NO + NO2 + HNO3 + PANs + other organic nitrates + HO2NO2 + HONO + NO3 + 2*N2O5 + particulate NO3- + …) is a useful tracer for characterizing air masses since it has a tendency to be conserved during airmass aging, as NOx is oxidized to other NOy species.

NOx (NO and NO2), NOy (total reactive nitrogen), and O3 are measured using the NCAR 4-channel chemiluminescence instrument, previously flown on the NASA WB-57F and the NCAR C130. NO is measured via addition of reagent O3 to the sample flow to generate the chemiluminescent reaction producing excited NO2, which is detected by photon counting with a dry-ice cooled photomultiplier tube. NO2 is measured as NO following photolytic conversion of NO2, with a time response of about 3 sec due to the residence time in the photolysis cell. NO is measured with an identical time response due to use of a matching volume. NOy is measured via Au-catalyzed conversion of reactive nitrogen species to NO, in the presence of CO, with a time response of slightly better than 1 sec. O3 is measured using the same chemiluminescent reaction but with the addition of reagent NO to the sample flow. Time response for the ozone measurement is slightly better than 1 s.

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Differential Absorption Lidar

The NASA Langley Airborne Differential Absorption Lidar (DIAL) system uses four lasers to make DIAL O3 profile measurements in the ultraviolet (UV) simultaneously with aerosol profile measurements in the visible and IR. Recent changes incorporate an additional laser and modifications to the receiver system that will provide aerosol backscatter, extinction, and depolarization profile measurements at three wavelengths (UV, visible, and NIR). For SEAC4RS, the DIAL instrument will include for the first time aerosol and cloud measurements implementing the High Spectral Resolution Lidar (HSRL) technique [Hair, 2008]. The modifications include integrating an additional 3-wavelength (355 nm, 532 nm, 1064 nm) narrowband laser and the receiver to make the following measurements; depolarization at all three wavelengths, aerosol/cloud backscatter and extinction at 532 nm via the HSRL technique, and aerosol/cloud backscatter at the 355 and 1064 nm via the standard backscatter lidar technique. Integration of the aerosol extinction profile at 532nm above and below the aircraft also provides aerosol optical depth (AOD) along the aircraft flight track.

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HOx Chemical Ionization Mass Spectrometer

An inlet collects ambient air from the free air stream and adds reagents, including O2 or N2 dilutents, and NO and SO2 reagent gases. This method, called "oxygen dilution modulation" leads to nearly 100% measurement of HO2 and RO2 in the O2 dilution/low reagent concentration mode, whereas RO2 is measured with less than 10% efficiency in the N2 dilution/higher reagent concentration mode. This is because the chemistry converts peroxy radicals to H2SO4 efficiently in the O2 mode, but RO2 radicals are converted to RONO in the N2 mode. The H2SO4 thus produced is ionized by reaction with NO3- ions. The reagent and product ions are detected by mass spectrometry using quadrupole mass filtering and counting by a channel electron multiplier operating in the negative ion mode.

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