Synonyms: 
DC8
DC-8
NASA DC8
NASA DC-8 -AFRC
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Fast Cloud Droplet Probe

SPEC has developed a Fast Cloud Droplet Probe (FCDP) with state-of-the-art electro-optics and electronics that utilizes forward scattering to determine cloud droplet distributions and concentrations in the range of 1.5 to 50 microns.  Though designed for cloud droplet measurements, the probe has also shown reliable measurements in ice clouds.  The new electronics include a temperature controlled fiber-coupled laser, FSSP-300 optics with pinhole limiting depth of field (Lance et al. 2010), a field programmable gate array (FPGA), 40 MHz analog-to-digital-converter (ADC) sampling, custom amplifiers, a very small and low power Linux based 400 MHz processor and a 16-Gigabyte flash drive that stores data at the probe.

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Laser Induced Fluorescence – Sulfur Dioxide

The LIF-SO2 instrument detects sulfur dioxide at the single-part per trillion (ppt) level using red-shifted laser-induced fluorescence. It has operated on the WB-57 and Global Hawk aircraft in the UT/LS, as well as on the DC-8. Sulfur Dioxide is an important precursor for aerosols including nucleation of new particles globally and can be greatly enhanced in the stratosphere following explosive volcanic eruptions. An important implication of the Asian Monsoon is transport of aerosol precursors including SO2 into the lower stratosphere.

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CSU QC-TILDAS Ammonia

Ambient ammonia (NH3) mixing ratios are measured in-situ using a flight-ready, closed-path, optical-based NH3 monitoring system. The CSU-NH3 instrument system consists of a combination of commercially-available and custom-built components including: 1) a commercially-available infrared absorption spectrometer that serves as the heart of the NH3 monitor, 2) a commercially-available inertial inlet that acts as a filter-less separator of particles from the sample stream, 3) a custom-built aircraft inlet, 4) a custom-designed vibration isolation mounting system for the spectrometer, and 5) an optional system for adding passivant to the sample stream.

The heart of the instrument is a closed-path, commercial (Aerodyne Research, Inc.), single-channel, quantum-cascade tunable infrared laser direct absorption spectrometer (QC-TILDAS) [McManus et al., 2010; McManus et al., 1995; Zahniser et al., 1995]. This spectrometer uses a direct absorption technique combined with a high sample flow rate (>10 SLPM) to achieve fast (up to 10 Hz) collection of absolute NH3 mixing ratios. The QC-TILDAS is operated with a heated aerodynamic separator (Aerodyne Research Inc., Inertial Inlet) that provides filter-less separation of particles >300 nm from the sample stream [Ellis et al., 2010]. An injection-style aircraft inlet allows calibration gases to be introduced into the sample stream within a few centimeters of the inlet tip. The custom inlet system is also designed to support the option for active continuous passivation of the sampling sufaces by 1H,1H-perflurooctylamine, a strong perfluorinated base that acts to coat the sampling surfaces with nonpolar chemical groups. Injection of this chemical into the aircraft inlet near the inlet tip prevents adsorption of both water and basic species on the sampling surfaces. The coating has been shown to greatly improve the instrument's time response in the laboratory and aboard research aircraft by increasing transmission of NH3 through the sample flow path [Pollack et al., 2019; Roscioli et al., 2016].

The QC-TILDAS is regularly calibrated on the ground and in flight via standard addition to the sample stream with a known concentration of NH3 generated from a temperature-regulated permeation tube (Kin-Tech), and zeroed by overflowing the inlet tip with a bottled source of NH3-free, synthetic air. The emission rate of the permeation device is calibrated before and after every mission by the NOAA ultraviolet optical absorption system [Neuman et al., 2003]. Allan variance analyses indicate that the in-flight precision of the instrument is 60 ppt at 1 Hz corresponding to a 3-sigma detection limit of 180 ppt. Zero signals span ±200 pptv, or 400 pptv total, with fluctuations in cabin pressure and temperature and altitude in flight. The total uncertainty associated with the 1-Hz measurement is ±(12% of the measured mixing ratio + 200 pptv).

The CSU-NH3 instrument has been successfully deployed (i.e. 100% data coverage) in two prior airborne research campaigns; one on the NSF/NCAR C-130 aircraft during the 2018 Western wildfire Experiment of Cloud Chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign and the other aboard the University of Wyoming King Air during the TRANS2Am field campaign in 2019, 2021, and 2022. The aircraft inlet and aerodynamic separator are currently being modified in the laboratory to support lower pressure altitudes such as those anticipated for the full altitude range of the NASA DC-8 aircraft.

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NSF/NCAR C-130, University of Wyoming King Air, DC-8 - AFRC
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Langley Cloud Probes

The LARGE group operates a suite of probes to measure in-situ cloud microphysical properties. Probes are typically mounted at an under-wing or wing-tip position in unperturbed air. The package of probes can be tailored to specific science objectives or mounting-point availability considerations. The following probes are available:

CAPS (Cloud, Aerosol, Precipitation Spectrometer), Droplet Measurement Technologies.  The CAPS contains individual sensors.  The CAS (Cloud Aerosol Spectrometer) measures size distributions of clouds and aerosols between 0.5-50µm diameter using forward-scattered light intensity from a 658nm laser. Response is calibrated with glass beads. The CIP (Cloud Imaging Spectrometer) measures size distributions of droplet and precipitation particles between 15-150µm diameter recording shadows on an optical array. The CIP is calibrated using a spinning disk. A hotwire is also used to measure total liquid-water-content. Each probe utilizes a local measurment of airspeed, temperature, and static pressure for quantification and has de-icing capability.
CDP (Cloud Droplet Probe), Droplet Measurement Technologies. The CDP measures droplet and aerosol size distributions between 2-50µm diameter using forward-scattering from a 658nm laser.  The probe is calibrated with glass beads and has de-icing capability.
WCM-2000 (Science Engineering Associates).  Measures Liquid Water Content (LWC) using two independent hotwire elements, Total Water Content (TWC) using a scoop sensor, and an element oriented parallel with the airstream as a control to establish the background response at that specific airspeed, temperature, and pressure.  Ice Water Content (IWC) is calculated as the difference between TWC and LWC. Each element operates by maintaining a constant temperature, and the current necessary to maintain that temperature is related directly with water content.  
 

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Langley Aerosol Mass Spectrometer

Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) operated by the Langley Aerosol Research Group Experiment (LARGE).  Provides fast-response non-refractory submicron aerosol mass concentrations (e.g., organics, sulfate, nitrate, ammonium, and chloride) and tracer m/z fragments (e.g., m/z44, m/z55, etc.).   

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Compact Airborne NO2 Experiment

The NASA GSFC Compact Airborne NO2 Experiment (CANOE) instrument measures nitrogen dioxide (NO2) on both pressurized and unpressurized (high-altitude) aircraft. Using non-resonant laser induced fluorescence (LIF), CANOE possesses the high sensitivity, fast time response, and dynamic range needed to observe NO2 throughout the troposphere and lower stratosphere.

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