Pacific Oxidants, Sulfur, Ice, Dehydration, and cONvection

NOAA Water (NW) is an airborne, two-channel, closed-path tunable diode laser absorption spectrometer developed by NOAA. It measures water vapor and enhanced total water content in the upper troposphere and lower stratosphere. Originally designed for NASA’s Global Hawk Uncrewed Aircraft System (UAS), it can also be deployed on other high-altitude aircraft. It uses second harmonic detection near 2.7 μm to measure water vapor. Its typical sampling frequency is 1 Hz.

The Cloud Particle Imager (CPI) is an airborne imager developed by SPEC Inc. It captures high-resolution (2.3 μm pixel size) images of cloud particles passing through its sampling volume. It uses a charge-coupled device (CCD) camera operating at 810 nm to record images and can capture up to 74 frames per second at a refresh rate of 40 Hz. The images from CPI can be used to determine microphysical properties such as particle size and shape.

The Fast Cloud Droplet Probe (FCDP) is an in situ airborne cloud probe manufactured by SPEC Inc. The FCDP measures cloud droplet concentration and size by detecting light scattered by particles. It detects particles with diameters from 1.5 to 50 microns and typically records measurements at 1 Hz.

The Laser Induced Fluorescence-Sulfur Dioxide (LIF-SO2) is an airborne optical sensor operated by NOAA to measure SO2 in the upper troposphere and lower stratosphere. It is based on single-photon laser-induced fluorescence and uses a tunable diode laser at 1084.5 nm to excite SO2 at 216.9 nm. It detects SO2 at a sampling rate of 1 Hz, with a detection limit of 5 pptv and an accuracy of 10%.

The PAN and Trace Hydrohalocarbon ExpeRiment (PANTHER) is an in situ airborne analyzer that uses electron capture detection and gas chromatography to measure trace gases, including methane, peroxyacyl nitrate (PAN), and carbon monoxide. PANTHER has a sampling frequency of 60 to 120 seconds and an accuracy of about 2% for most species, except PAN, which is 10%. The development of PANTHER was funded by NASA’s Instrument Incubator Program and NOAA’s Climate and Global Change Program.

The Meteorological Measurement System (MMS) is an in situ airborne instrument that measures atmospheric state parameters. MMS provides high-resolution, accurate measurements of atmospheric pressure, temperature, and wind direction and speed immediately around the aircraft. Additional parameters that can be derived include potential temperature, true airspeed, turbulence dissipation rate, and Reynolds number. Measurements of all parameters are typically collected at a rate of 20 Hz.

The Printed Optical Particle Spectrometer (POPS) is an in situ spectrometer that measures particle size and concentration. POPS can be mounted on UAVs or balloons to collect vertical aerosol particle profiles. Operating at a typical wavelength of 405 nm, POPS provides measurements roughly every second and detects particles from 140 nm to 3000 nm.

The Whole Air Sampler (WAS) is an airborne in situ instrument that collects air samples for analyzing trace gases, including nonmethane hydrocarbons (NMHCs), halocarbons, alkyl nitrates, and various sulfur compounds in the troposphere. Air samples collected by the WAS are then analyzed using gas chromatography and mass spectrometry to identify the gases present. The WAS collects samples every minute, allowing scientists to obtain a clear picture of the environment's chemical composition as research aircraft pass through.

The Small Ice Detector 3 (SID-3) is an in situ airborne particle imager developed by the University of Hertfordshire. It measures high-resolution angular scattering patterns of individual cloud particles to determine particle size distribution and number concentration. It operates at 532 nm and detects particles from 5 to 50 μm. SID-3 provides number concentration measurements typically every 1 second and particle size distribution measurements every 10 seconds.

The Uncrewed Aircraft Systems (UAS) Chromatograph for Atmospheric Trace Species (UCATS) is an in situ airborne instrument suite that measures atmospheric trace gases. It comprises three instruments: a three-channel gas chromatograph (GC), a dual-beam ozone photometer (OZ), and a tunable diode laser (TDL) spectrometer. The GC measures nitrous oxide (N2O) and sulfur hexafluoride (SF6) every 70 seconds and detects hydrogen (H2), methane (CH4), and carbon monoxide (CO) every 140 seconds. The OZ sensor operates at 254 nm and provides ozone measurements every 10 seconds. The TDL spectrometer operates at 1370 nm and provides water vapor measurements every 1 second. UCATS was designed for operation on UAS but has also been deployed on piloted aircraft.

The Diode Laser Hygrometer (DLH) is an in situ airborne hygrometer developed by NASA’s Langley Research Center (LaRC). It uses tunable diode laser absorption to detect atmospheric water vapor. DLH operates in the near-infrared at about 1.4 μm and has a measurement frequency of 100 Hz. It can deliver precise water vapor measurements even when flying through clouds.

The 2D-Stereo Particle Probe (2D-S) is an in situ airborne optical imaging device developed by SPEC Inc. It uses two diode-laser beams to create stereo images of cloud particles via linear-array shadowing. These images enable determination of cloud particle size distribution, particle number concentration, and ice or liquid water content. 2D-S has a resolution of 10 µm and can measure hydrometeors from 25 to 1280 µm.

The NOAA Dual-Beam UV-Absorption Ozone Photometer (NOAA-O3) is an in situ optical balloon-borne and airborne instrument that measures ozone concentrations in the troposphere and lower stratosphere. It operates at 254 nm, enabling calculation of ozone number density from the precise ozone absorption cross section at that wavelength. It has a sampling rate of 2 Hz and a horizontal resolution of 100 to 200 meters during typical research flights.