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.

Instrument Type: 
Aircraft: 
Point(s) of Contact: 

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.

Measurements: 
Aircraft: 
Point(s) of Contact: 

Alpha Jet Ozone Instrument

Alpha Jet (O3) Ozone instrument details

Measurements of ozone (O3) mixing ratios are performed using a commercial O3 monitor (2B Technologies Inc., model 205 (http://www.twobtech.com/model_205.htm)) based on ultraviolet (UV) absorption techniques and modified for flight worthiness. The dual-beam instrument uses two detection cells to simultaneously measure UV light intensity differences between O3-scrubbed air and un-scrubbed air to give precise measurements of O3. The monitor has been modified by upgrading the pressure sensor and pump to allow measurements at high altitudes, including a lamp heater to improve the stability of the UV source, and the addition of heaters, temperature controllers and vibration isolators to control the monitor’s physical environment.

Ozone inlet

The air intake is through Teflon tubing (perfluroalkoxy-polymer, PFA) with a backward-facing inlet positioned on the underside of the instrument wing pod. Air is delivered through a 5 µm PTFE (polytetrafluroethylene) membrane filter to remove fine particles prior to analysis.

Ozone instrument calibrations:

The O3 monitor has undergone thorough instrument testing in the laboratory to determine the precision, linearity and overall accuracy. Eight-point calibration tests (ranging from 0 – 300 ppbv) are typically performed before and after each flight using an O3 calibration source (2B Technologies, model 306 referenced to the WMO scale). The calibration of all 2B Technologies Ozone Calibration Sources is traceable to NIST through an unbroken chain of comparisons and is sent back to the vendor annually for calibration. Calibrations in a pressure- and temperature-controlled environmental chamber have also been carried out using the O3 calibration source over the pressure range 200 - 800 mbar and temperature range -15 to +25 ⁰C; typical pressure and temperature ranges observed in the wing-mounted instrument pod during flight.

Instrument Type: 
Measurements: 
Aircraft: 
Point(s) of Contact: 

Harvard University Picarro Cavity Ring Down Spectrometer

Instrument Type: 
Measurements: 
Point(s) of Contact: 

In-Situ Measurements of Aerosol Optical Properties

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.

Instrument Type: 
Aircraft: 
Point(s) of Contact: 

Differential Aerosol Sizing and Hygroscopicity Spectrometer Probe

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 campaigns.

Measurements: 
Point(s) of Contact: 

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].

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

Closed-path Laser Hygrometer 2

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, which has been flown on the NASA DC-8 and WB-57F and the NSF/NCAR G-V and C-130. This version of the instrument 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.

Measurements: 
Aircraft: 
Gulfstream V - NSF
Point(s) of Contact: 

Three-View Cloud Particle Imager

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.

Measurements: 
Aircraft: 
Gulfstream V - NSF
Point(s) of Contact: 

Picarro G1301-c Methane/Carbon Dioxide Analyzer

The Picarro CO2/CH4 Flight Analyzer is a real time, trace gas monitor capable of measuring these gases with parts-per-billion (ppbv) sensitivity onboard aircraft with varying cabin pressure and environmental conditions. 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.

Instrument Type: 
Measurements: 
Aircraft: 
Gulfstream V - NSF
Point(s) of Contact: 

Pages

Subscribe to RSS - Spectrometer (in situ)