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. Therefore, the uncertainty associated with the 1-Hz measurement is ±12% of the measured NH3 mixing ratio plus the 400 pptv detection limit.

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 test flights in fall 2019. 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
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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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DC-8 - AFRC, P-3 Orion - WFF, HU-25 Falcon - LaRC, C-130 - WFF
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CU Aircraft Extractive Electrospray Time-of-Flight Mass Spectrometer

Principle: The CU aircraft Extractive Electrospray Time-of-Flight Mass Spectrometer (EESI-TOFMS) detects the chemical composition of submicron particulate matter by simultaneous dissolution of the aerosol and soft ionization of its molecular components in an electrospray, followed by detection using time-of-flight mass spectrometry. When operated with positive ion polarity analytes are detected intact as adducts with sodium ions. When operated with negative ion polarity analytes are detected as deprotonated anions.

 

Aircraft Operation: Operated with positive or negative ion polarity, depending on mission goals.

Pressure-controlled EESI region with a maximum sampling altitude of 23 kft. Sensitivity can be increased for boundary layer  sampling by increasing the pressure of the electrospray region.

Calibrated relative to AMS on flight days, and confirmed with absolute calibrations on maintenance days

1s time resolution with 15s background measurements every 4 min.

 

Data Products: 

Positive ion polarity EESI(+): C6H10O5 calibrated as levoglucosan and C6H5NO4 calibrated as nitrocatechol

Negative ion polarity EESI(-): C6H5NO4 calibrated as nitrocatechol
Additional species under development. Species of interest for specific campaigns can be tested and calibrated for.

 

Detection Limits (1s):

C6H10O5 as levoglucosan: 200 ng sm-3

C6H5NO4 as nitrocatechol: 20ng sm-3 EESI(-), 400 ng sm-3 EESI(+)

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G2301-m

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G2301-f

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OSCAR lab

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OSCAR portable

TBD

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NOAA Picarro

The Picarro G2401m is a commerical instrument that measures CO2, CH4, CO, and H2O. The analyzer is based on Wavelength-Scanned Cavity Ring Down Spectroscopy (WS-CRDS), a time-based measurement utilizing a near-infrared laser to measure a spectral signature of the molecule. Gas is circulated in an optical measurement cavity with an effective path length of up to 20 kilometers. A patented, high-precision wavelength monitor makes certain that only the spectral feature of interest is being monitored, greatly reducing the analyzer’s sensitivity to interfering gas species, and enabling ultra-trace gas concentration measurements even if there are other gases present. As a result, the analyzer maintains high linearity, precision, and accuracy over changing environmental conditions with minimal calibration required.

The measurement software of the NOAA Picarro has been modified to have a shorter measurement interval (~1.2 seconds instead of ~2.4 seconds) by reducing the number of scans of the CO spectroscopic peak and therefore yielding a less-precise CO measurement (1σ on 1-2 second measurements is ~9 ppb instead of ~4 ppb). The instrument was also modified to have a lower cell pressure set point (80 torr instead of 140 torr) to allow it to operate across the full pressure altitude range of the DC8 without requiring upstream pressurization of the sample stream.

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In Situ Measurements of Aerosol Microphysical Properties

Five instruments, two nucleation-mode aerosol size spectrometers (NMASS; Williamson et al., 2018), two ultra-high sensitivity aerosol spectrometers (UHSAS; Kupc et al., 2018), and a laser aerosol spectrometer (LAS) comprise the AMP package. The AMP package provides particle size distributions with up to one-second time resolution for dry aerosol particles between 0.003 and 4.8 µm in diameter. Details of methods, uncertainties, and data products from the AMP package are in Brock et al. (2019). During ATom, the instruments were used to investigate how particles in the remote atmosphere influence climate by examining the origin of small particles in the remote atmosphere and their growth to sizes where they can affect clouds and the sources, characteristics, and distribution of soil dust and sea-spray particles, and 3) the importance long-range transport from human and natural sources on background aerosol properties.

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Harvard Tracer Suite

HTS is composed of two instruments based on absorption of near-infrared laser radiation in high finesse optical cavities. A Picarro G2401-m analyzer based on wavelength-scanned cavity ring-down spectroscopy (CRDS) measures CO2, CH4, and CO concentrations at 2-second intervals. A Los Gatos 913-0014 EP analyzer based on off-axis integrated cavity output spectroscopy (ICOS) measures N2O and CO concentrations at 1-second intervals. Extensive modifications have been applied to these commercial analyzers for flight and include vibration isolation, temperature control, additional flow control and pumping capacity for high-altitude sampling, sample drying, and in-flight calibrations using WMO-traceable compressed gas standards to verify stable and accurate performance throughout the full DC-8 flight envelope.

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