Synonyms: 
KORUS-AQ (HL 5200)
Associated content: 

In Situ Airborne Formaldehyde

The NASA GSFC In Situ Airborne Formaldehyde (ISAF) instrument measures formaldehyde (CH2O) on both pressurized and unpressurized (high-altitude) aircraft. Using laser induced fluorescence (LIF), ISAF possesses the high sensitivity, fast time response, and dynamic range needed to observe CH2O throughout the troposphere and lower stratosphere, where concentrations can range from 10 pptv to hundreds of ppbv.

Formaldehyde is produced via the oxidation of hydrocarbons, notably methane (a ubiquitous greenhouse gas) and isoprene (the primary hydrocarbon emitted by vegetation). Observations of CH2O can thus provide information on many atmospheric processes, including:
 - Convective transport of air from the surface to the upper troposphere
 - Emissions of reactive hydrocarbons from cities, forests, and fires
 - Atmospheric oxidizing capacity, which relates to formation of ozone and destruction of methane
In situ observations of CH2O are also crucial for validating retrievals from satellite instruments, such as OMI, TROPOMI, and TEMPO.

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Compact Atmospheric Multispecies Spectrometer

The CAMS instrument’s core design and operation is similar to the DFGAS (Difference Frequency Generation Absorption Spectrometer) instrument, which has been successfully deployed for fast, accurate, and sensitive airborne measurements of the important trace gas formaldehyde (CH2O). CAMS like DFGAS is based on tunable mid-IR (3.53-μm) absorption spectroscopy utilizing advanced fiber optically pumped difference-frequency generation (DFG) laser sources. Mid-Infrared light at 2831.6-cm-1 (3.53 μm) is generated by mixing two near-IR room temperature lasers (one at 1562 nm and the other at 1083 nm) in a non-linear crystal (periodically poled lithium niobate). The DFG laser output is directed through a multipass Herriott absorption cell (90-m pathlength in ~ 1.7 liter volume) where the laser light is selectively absorbed by a moderately strong and isolated vibrational-rotational absorption feature of CH2O. The transmitted light from the cell is directed onto an IR detector employing a number of optical elements. A portion of the IR beam is split off by a special beam splitter (BS) before the multipass cell and focused onto an Amplitude Modulation Detector (AMD) to capture and remove optical noise from various components in the difference frequency generation process. A third detection channel from light emanating out the back of the beam splitter is directed through a low pressure CH2O reference cell and onto a reference detector (RD) for locking the center of the wavelength scan to the absorption line center. The mid-IR DFG output is simultaneously scanned and modulated over the CH2O absorption feature, and the second harmonic signals at twice the modulation frequency from the 3 detectors are processed using a computer lock-in amplifier [Weibring et al., 2006].

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Gulfstream V - NSF, DC-8 - AFRC
Point(s) of Contact: 
Alan Fried (Co-I)

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 chemical ionization mass spectrometry technique that allows for fast measurements of organic trace gases. In combination with the CHARON inlet, it measures the organic composition of submicrometer aerosol particles.

 

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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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Atmospheric Vertical Observations of CO2 in the Earth's Troposphere

The NASA Langley CO2 sampling system (AVOCET) has an extensive measurement heritage in tropospheric field campaigns, delivering high reliability over 3400 flight hours (452 science flights) and is recognized within the CO2 community as a benchmark for evaluating newly evolving remote CO2. This instrument was adapted by the investigators for airborne sampling and has been successfully deployed aboard NASA research aircraft beginning with the PEM-West A mission in 1992, and more recently during the 2016 KORUS-AQ, 2017 ACSENDS/ABoVE, and 2019 FIREX-AQ missions. The newest iteration of the technique as of 2017 has at its core a modified LI-COR model 7000 non-dispersive infrared spectrometer (NDIR). The basic instrument is small (13 x 25 x 37 cm) and composed of dual 11.9 cm^3 sample/reference cells, a feedback stabilized infrared source, 500 Hz chopper, thermoelectrically-cooled solid state PbSe detector, and a narrow band (150 nm) interference filter centered on the 4.26 μm CO2 absorption band. Using synchronous signal detection techniques, it operates by sensing the difference in light absorption between the continuously flowing sample and reference gases occupying each side of the dual absorption cell. Thus, by selecting a reference gas of approximately the same concentration as background air (~405 ppm), minute fluctuations in atmospheric concentration can be quantified with high precision. Calibrations are performed frequently during flight using WMO-traceable standards from NOAA ESRL. Precisions of ≤ 0.1 ppm (±1σ) for 1 Hz sampling rates are typical for our present airborne CO2 system when operated at 600 torr sample pressure.

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CU Aircraft High-Resolution Time-of-Flight Aerosol Mass Spectrometer

Principle: The CU aircraft version of the Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) detects non-refractory submicron aerosol composition by impaction on a vaporizer at 600°C, followed by electron ionization and time-of-flight mass spectral analysis. Size-resolved composition can be quantified by measuring the arrival times of the aerosol at the vaporizer.

Aircraft Operation: (1 min cycles, can be adjusted to meet mission goals):
46 s total concentration measurements (1 s resolution, can be increased to up to 10 Hz upon request)
5 s speciated size distribution measurements (with improved S/N detection due to ePToF acquisition)
9 s Background + Overhead
Higher accuracy due to flight day calibrations using built-in system
Custom pressure controlled inlet with confirmed performance up to 45 kft

Real Time Data Products: 
PM1 Aerosol Mass Concentrations:
Organic aerosol (OA) , SO4, NO3, NH4, Chloride 
OA Chemical Markers: f44 (Secondary OA), f57 (hydrocarbon-like OA), f60 (biomass burning OA), f82 (isoprene epoxide-SOA), other fx upon request

More Advanced Products:
- PM1 Seasalt, ClO4, total I, total Br, MSA concentrations
- O/C, H/C, OA/OC, OSc
- Particle organic nitrates (pRONO2)
- Ammonium Balance, estimated pH
- OA components by positive matrix factorization (PMF)
- Particle eddy covariance fluxes of all species
- Speciated Aerosol size distributions

Detection Limits (1s, ng sm-3), (1 min, ng sm-3) from start of the flight (due to custom cryopump):
Sulfate: 40, 15
Nitrate: 15, 6
Ammonium: 3, 1
Chloride: 30, 12
OA: 200, 80
For detailed OA analysis, longer averaging (3-30 s, depending on OA concentration) is needed. A 1 min product is hence provided as well.

 

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Langley Aerosol Research Group Experiment

Langley Aerosol Research Group Experiment (LARGE).  The "classic" suite of instrumenation measures in-situ aerosol micrphysical and optical properties. The package can be tailored for specific science objectives and to operate on a variety of aircraft. Depending on the aircraft, measurments are made from either a shrouded single-diffuser "Clarke" inlet, from a BMI (Brechtel Manufacturing Inc.) isokinetic inlet, or from a HIML inlet. Primary measurements include:

1.) total and non-volatile particle concentrations (3nm and 10nm nominal size cuts),
2.) dry size distributions from 3nm to 5µm diameter using a combination of mobilty-optical-aerodynamic sizing techniques,
3.) dry and humidified scattering coefficients (at 450, 550, and 700nm wavelength), and
4.) dry absorption coefficients (470, 532, and 670nm wavelength). 

LARGE derived products include particle size statistics (integrated number, surface area, and volume concentrations for ultrafine, accumulation, and coarse modes), dry and ambient aerosol extinction coefficients, single scattering albedo, angstrom exponent coefficients, and scattering hygroscopicity parameter f(RH).

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DC-8 - AFRC, C-130H - WFF, P-3 Orion - WFF, HU-25 Falcon - LaRC, King Air B-200 - LaRC, Twin Otter - CIRPAS - NPS
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Soluble Acidic Gases and Aerosols

As part of the measurement team on the NASA DC-8 we operate two related installations: a mist chamber/ion chromatograph (MC/IC) sampling/analysis system providing near real time results for selected species, and a bulk aerosol system that collects particulates onto filters for subsequent analysis. We use ion chromatography on aqueous extracts of the bulk aerosol samples collected on Teflon filters to quantify soluble ions (Cl-, Br-, NO3-, SO42-, C2O42-, Na+, NH4+, K+, Ca+, and Mg+). Filters are exposed on all level flight legs. Below 3 km exposure times are 5 minutes or less, increasing at higher altitudes to a maximum sample time of 15 minutes. Aerosols participate in heterogeneous chemistry, impact radiative transfer, and can be detected from space. Our measurements help to validate and extend retrievals of aerosol distributions and properties by MODIS, MISR and CALIPSO. In addition, several of the particle-associated ions are tracers of sources of gas and aerosol pollutants (e.g., SO42- from industrial emissions of SO2, enhancements of C2O42-, K+, and NH4+ indicate encounters with biomass burning plumes, Na+, and Cl- are tracers of seasalt, Mg2+ and Ca2+ are tracers of dust). Our system has two inlets, allowing collection of paired samples simultaneously.

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