NASA - National Aeronautics and Space Administration

Two instruments,a nucleation-mode aerosol size spectrometers (NMASS; Williamson et al., 2018), and an ultra-high sensitivity aerosol spectrometers (UHSAS; Kupc et al., 2018) comprise the AMP package for ACCLIP. The AMP package provides particle size distributions with up to one-second time resolution for dry aerosol particles between 0.003 and 1.5 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.

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.

Three instruments, a cavity ringdown (CRD) aerosol extinction spectrometer, a photoacoustic absorption spectrometer (PAS), and an ultra-high sensitivity aerosol size spectrometer (UHSAS) comprise the AOP package. The AOP package provides multi‐wavelength, multi-RH aerosol extinction and absorption measurements with fast response and excellent accuracy and stability on aircraft platforms. The instruments will also characterize the optics of black carbon (BC) mixing state, brown carbon, and water uptake of aerosol. Aerosol asymmetry parameter, needed for radiative transfer modeling, will be calculated from dry and humidified particle size distributions.

The DASH-SP providse rapid measurements of size-resolved aerosol sub-saturated hygroscopic growth factors and the real part of aerosol refractive index. It has been deployed aboard the NASA DC-8 during the DC3 and SEAC4RS field campaign and also on the P3 during ARCSIX (May-Aug 2024).

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].

The University of Colorado Closed-path Laser Hygrometer, version 2 (CLH2) is an infrared absorption instrument designed to measure so-called “total water”, the sum of water vapor and particulate water. It is a second-generation sensor that derives from the original CLH and was developed for the NSF DC3 campaign in 2011 as an alternative to the NCAR CVI for measurements of cloudwater contents. It has flown on the NASA DC-8 and the NSF/NCAR G-V and C-130. The most recent campaign was NSF SOCRATES in 2018. CLH-2 uses a fiber-coupled tunable diode laser at 1.37 μm to measure by absorption the water vapor resulting from the evaporation of cloud particles. The spectrometer will be housed in a modified PMS canister and coupled to a heated forward-facing inlet. Sampling of particles is deliberately sub-isokinetic, which results in enhancements of particle mass relative to ambient by factors ranging between 30 and 70. Therefore, condensed water even in very thin clouds can be measured with high precision and accuracy.

The Three-View Cloud Particle Imager (3V-CPI) measures the size, shape and concentration of water drops and ice particles in clouds. The probe is a combination of three imaging instruments. Two of them comprise a 2D-S (Two- Dimensional Stereo hydrometeor spectrometer), in which two high-resolution (about 9 mm resolution) 2D probes image particles as they pass through laser beams that are orthogonal to each other. If particles also lie in the intersection of the sensitive areas of the two beams, they are seen by both 2D probes. In that case, the third instrument, a Cloud Particle Imager (CPI), is triggered to take a high-resolution picture, via a briefly illuminated high-resolution imaging array. This image has a pixel size of about 2.3 µm and so provides very high resolution for determining shapes and habits of ice crystals. The probe is particularly suited to imaging such crystals, but also provides good detection of other hydrometeors including large cloud droplets, drizzle and small rain drops, and other precipitation particles.