NASA - National Aeronautics and Space Administration

Solar viewing Fourier Transform Interferometer (FTIR). This is a ground based instrument stationed at the NOAA Mauna Loa Observatory (MLO). It operates daily in an autonomous mode taking middle infrared solar spectra of the terrestrial atmosphere. It began operation in 1995 and has run continuously since. The data are used for long term studies of many trace species in the atmosphere. Its operated as part of the Network for the Detection for Atmospheric Composition Change (NDACC www.ndacc.org). See https://www2.acom.ucar.edu/irwg for information on the network and https://www2.acom.ucar.edu/irwg for info on PI J. Hannigan. Data are publicly available at www.ndacc.org. Data products consist of retrievals from the remote sensing spectra of vertical profiles of CO, CH4, ClONO2, HCOOH, C2H6, HCN, HCl, HF, HNO3, H2O, HDO, OCS, N2O, O3, H2CO. Other species are available.

Targeting Fourier Transform Spectrometer (FTS) measuring infrared spectra from 4.5 to 13.4 µm. AES was the airborne testbed for the EOS/Aura TES instrument and operated ~1994-2000.

The NASA Rapid OZone Experiment (ROZE) is an in situ instrument capable of measuring ozone (O3) throughout the troposphere and lower stratosphere on airborne platforms. The instrument uses cavity-enhanced absorption to measure the amount of ozone in a sampled volume flowing through an optical cell. The high-sensitivity of the cavity-enhanced detection scheme and the small sample volume enable high precision measurements in short integration times, making this instrument suitable for measuring O₃ fluxes (the exchange between the Earth's surface and atmosphere) with the eddy covariance technique. The instrument is designed for autonomous operation and requires minimal support (and no gases or dry ice) in the field. An inlet mounted in the free stream is needed to sample ambient air.

4STAR (Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research; Dunagan et al., 2013) is an airborne sun-sky spectrophotometer measuring direct solar beam transmittance (i.e., 4STAR determines direct solar beam transmission by detecting direct solar irradiance) and narrow field-of-view sky radiance to retrieve and remotely sense column-integrated and, in some cases, vertically resolved information on aerosols, clouds, and trace gases. The 4STAR team is a world leader in airborne sun-sky photometry, building on 4STAR’s predecessor instrument, AATS-14 (the NASA Ames Airborne Tracking Sun photometers; Matsumoto et al., 1987; Russell et al. 1999, and cited in more than 100 publication) and greatly expanding aerosol observations from the ground-based AERONET network of sun-sky photometers (Holben et al., 1998) and the Pandora network of ground-based direct-sun and sky spectrometer (e.g, Herman et al., 2009).

4STAR is used to quantify the attenuated solar light (from 350 to 1650 nm) and retrieve properties of various atmospheric constituents: spectral Aerosol Optical Depth (AOD) from ultraviolet to the shortwave infrared (e.g., LeBlanc et al., 2020, Shinozuka et al., 2013); aerosol intensive properties - Single Scattering Albedo (SSA; e.g., Pistone et al., 2019), asymmetry parameter, scattering phase function, absorption angstrom exponent, size distribution, and index of refraction; various column trace gas components (NO₂, Ozone, Water Vapor; e.g., Segal-Rosenheimer et al., 2014, with potential for SO₂ and CH₂O); and cloud optical depth, effective radius and thermodynamic phase (e.g., LeBlanc et al., 2015).

Some examples of the science questions that 4STAR have pursued in the past and will continue to address:

• What is the Direct Aerosol Radiative Effect on climate and its uncertainty? (1)
• How much light is absorbed by aerosol emitted through biomass burning? (1)
• How does heating of the atmosphere by absorbing aerosol impact large scale climate and weather patterns? (1)
• How does aerosol spatial consistency of extensive and intensive properties compare? (2)
• How does the presence of aerosol impact Earth’s radiative transfer, with co-located high concentration of trace gas? (3, 5)
• What is the impact of air quality from long-range transport of both aerosol particulates and column NO2 and Ozone, and their evolution? (3, 6)
• What are the governing properties and spatial patterns of local and transported aerosol? (1)
• How are cloud properties impacted near the sea-ice edge? (4)
• In heterogeneous environments where clouds and aerosols are present, how much solar radiation is impacted by 3D radiative transfer? And how does that impact the aerosol properties? (5)

(1) ORACLES: Zuidema et al., doi:10.1175/BAMS-D-15-00082.1., 2016; LeBlanc et al., doi:10.5194/acp-20-1565-2020, 2020; Pistone et al., https://doi.org/10.5194/acp-2019-142, 2019;Cochrane et al., https://doi.org/10.5194/amt-12-6505-2019, 2019; Shinozuka et al., https://doi.org/10.5194/acp-20-11275-2020, 2020; Shinozuka et al., https://doi.org/10.5194/acp-20-11491-2020, 2020
(2) KORUS-AQ:  LeBlanc et al., doi:https://doi.org/10.5194/acp-22-11275-2022, 2022

(3) KORUS-AQ: Herman et al., doi:10.5194/amt-11-4583-2018, 2018
(4) ARISE: Smith et al., https://doi.org/10.1175/BAMS-D-14-00277.1, 2017; Segal-Rosenheimer et al., doi:10.1029/2018JD028349, 2018
(5) SEAC4RS: Song et al., doi: 10.5194/acp-16-13791-2016, 2016; Toon et al., https://doi.org/10.1002/2015JD024297, 2016
(6) TCAP: Shinozuka et al., doi:10.1002/2013JD020596, 2013; Segal-Rosenheimer et al., doi:10.1002/2013JD020884, 2014

The NOAA NOyO₃ 4-channel chemiluminescence (CL) instrument will provide in-situ measurements of nitric oxide (NO), nitrogen dioxide (NO₂), total reactive nitrogen oxides (NO_y), and ozone (O₃) on the NASA DC-8 during the FIREX-AQ project. Different versions of this instrument have flown on the NASA DC-8 and NOAA WP-3D research aircraft on field projects since 1995. It provides fast-response, specific, high precision, and calibrated measurements of nitrogen oxides and ozone at a spatial resolution of better than 100m at typical DC-8 research flight speeds. Detection is based on the gas-phase CL reaction of NO with O₃ at low pressure, resulting in photoemission from electronically excited NO₂. Photons are detected and quantified using pulse counting techniques, providing ~5 to 10 part-per-trillion by volume (pptv) precision at 1 Hz data rates. One detector of the integrated 4-channel instrument is used to measure ambient NO directly, a second detector is equipped with a UV-LED converter to photodissociate ambient NO₂ to NO, and a third detector is equipped with a heated gold catalyst to reduce ambient NOy species to NO. Reagent ozone is added to these sample streams to drive the CL reactions with NO. Ambient O₃ is detected in the fourth channel by adding reagent NO.

The operating principle of the O3 instrument is the measurement of chemiluminescence from the reaction of nitric oxide (NO) with ambient O3 using a dry-ice cooled, red-sensitive photomultiplier employing photon counting electronics. The reagent NO (grade > 99%) is supplied from a commercially purchased lecture bottle filled to a maximum pressure of 500 psig. Since NO is a toxic gas, the small high pressure cylinder, its regulator, and several safety features are contained inside a specially designed pressure safe vessel that is vented overboard the aircraft. Ambient air is sampled through a standard HIMIL inlet protruding outside the aircraft boundary layer. Ambient air sample flow is controlled to 500 sccm, while the NO reagent is introduced to the reaction vessel in near-excess flow of ~ 4 sccm. Gas flows as well as the reaction vessel temperature (35 ± 0.1°C) and pressure (10 ± 0.05 torr) are all controlled at constant conditions resulting in maximum stability of the detected signal and instrument sensitivity. The instrument sensitivity (~2000 cps/ppbv) is determined from calibrations performed on the ground before and after each flight or set of back-to-back flights using a UV absorption based calibrator (TECO model 49PS) operated with high-quality ultra-pure air. A near-linear calibration curve is generated in 100 ppb intervals from 0 to 1 ppm. This calibration range is sufficient to measure O3 mixing ratios over the altitude range of the aircraft.

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.

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.

The Unmanned Aircraft Systems (UAS) Chromatograph for Atmospheric Trace Species (UCATS) was designed and built for autonomous operation on remotely piloted aircraft, but has also been used on manned aircraft. It uses chromatography to separate atmospheric trace gases along narrow heated columns, followed by precise and accurate detection with electron capture detectors. There are currently three chromatography channels on UCATS, which measure nitrous oxide (N2O) and sulfur hexafluoride (SF6); CFC-11, CFC-12, CFC-113, and halon 1211; and chloroform (CHCl3) and carbon tetrachloride. On an earlier version of UCATS, with only two channels, we also measured methane, hydrogen, and carbon monoxide, along with N2O and SF6. In addition, there is a small ozone instrument and a tunable diode laser instrument for water vapor. Gas is pumped into the instruments from an inlet outside the aircraft, measured, and vented. UCATS has flown on the Altair UAS, the GV during HIPPO, the NASA Global Hawk UAS during the Global Hawk Pacific (GloPac) and ATTREX missions, where a record was set for the longest duration research flight (more than 28 hours), the DC-8 for ATom, and the ER-2 for DCOTSS. UCATS is relatively lightweight and compact, making it ideal for smaller platforms, but it is easily adaptable to a mid-size platform like the GV or Global Hawk. The data are used to measure sources and sinks of trace gases involved in climate and air quality, as well as transport through the atmosphere.

UCATS is three different instruments in one enclosure:

1. 3-channel (formerly 2-channel, up until 2020) gas chromatograph (GC)
2. Dual-beam ozone photometer (OZ)
3. Tunable diode laser (TDL) spectrometer for water vapor (WV)