Associated content: 

Diode Laser Hygrometer

The DLH has been successfully flown during many previous field campaigns on several aircraft, most recently ATom, KORUS-AQ, and SEAC4RS (DC-8), POSIDON (WB-57), CARAFE (Sherpa), DISCOVER-AQ (P-3), and ATTREX (Global Hawk). This sensor measures water vapor (H2O(v)) via absorption by one of three strong, isolated lines in the (101) combination band near 1.4 μm and is comprised of a compact laser transceiver mounted to a DC-­8 window plate and a sheet of high grade retroflecting road sign material applied to an outboard DC‐8 engine housing to complete the optical path. Using differential absorption detection techniques, H2O(v) is sensed along the 28.5m 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 that are measured in the laboratory. Preliminary water vapor mixing ratio and derived relative humidities are provided in real-time to investigators aboard the DC-8.

Instrument Type: 
Measurements: 
Instrument Team: 

CCD Actinic Flux Spectroradiometers

The CCD Actinic Flux Spectroradiometers (CAFS) developed in the ARIM laboratory will be deployed on the NASA DC-8 for SEAC4RS and DC3 field campaigns. The instruments measure spectrally resolved down- and up-welling in situ ultraviolet and visible actinic flux from approximately 280-650 nm. Photolysis frequencies for photodissociation reactions for species including O3, NO2, CH2O, HONO, HNO3, N2O5, HO2NO2, PAN, H2O2, CH3OOH, CH3ONO2, CH3CH2ONO2, CH3COCH3, CH3CHO, CH3CH2CHO, CHOCHO, CH3COCHO, CH3CH2CH2CHO, CH3COCH2CH3, Br2, BrO, Br2O, BrNO3, BrCl, HOBr, BrONO2, Cl2, ClO, and ClONO2 are calculated from the radiative measurements. Careful calibration techniques and comparison to the NCAR/TUV radiative transfer model improves the accuracy and precision of the measurements. CAFS instruments have a successful heritage of radiation measurements during atmospheric chemistry and satellite validation missions including NASA AVE, PAVE, CR-AVE, TC-4 and ARCTAS campaigns on the WB-57 and DC-8 platforms and during the NSF OASIS ground campaign in Barrow, AK. Similar instruments will be deployed on the NCAR G-V platform as part of the HIAPER Airborne Radiation Package (HARP) as a part of DC3 and SEAC4RS. In situ solar radiation measurements are critical to NASA atmospheric composition research. Actinic flux radiation drives the chemistry of the atmosphere, including the evolution of ozone, greenhouse gases, biomass burning, and other anthropogenic and natural trace constituents. The evolution of boundary layer and tropospheric constituents convected to the upper troposphere and lower stratosphere requires knowledge of the complex radiative fields expected during the campaigns. The gases, in turn, control the chemical evolution of aerosols.

Instrument Type: 
Measurements: 
Instrument Team: 

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).

Instrument Type: 
Measurements: 
Instrument Team: 

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.

Instrument Type: 
Measurements: 
Aircraft: 
Instrument Team: 

Pages

Subscribe to RSS - ATom