WB-57 - JSC

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.

Many changes from the original Chlorine Nitrate instrument. NO2 instrument removed. New inlet with orifice for one halogen duct, addition of vacuum scroll pump, new RF oscillators and amplifiers, new RF frequency, new lamp housings and cooling for lamp modules. Flew in MACPEX without dissociation heaters, i.e., focus on BrO and ClO measurements and not measure ClONO2 or ClOOCl.

32 samples/flight (ER-2); 50 samples/flight (WB57); 90 samples/flight (Global Hawk)

Updated control system with remote control capability

Fill times
–14 km 30 – 40 sec
–16 km 40 – 50 sec
–18 km 50 – 60 sec
–20 km 100 – 120 sec (estimated)

Analysis in UM lab: GC/MS; GC/FID; GC/ECD

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.

HIRAD is a multi-frequency, hurricane imaging, interferometric single-pol passive C-band radiometer, operating from 4 GHz to 7 GHz, with both cross-track and along-track resolution that measures strong ocean surface winds through heavy rain from an aircraft or space-based platform. A one-dimensional thinned synthetic aperture array antenna is used to obtain wide-swath measurements with multiple simultaneous beams in a push-broom configuration. HIRAD features software beam forming with no moving parts, internal hot, cold, and noise diode based calibration, and continuous, gap-free imaging. Its swath width is approximately 60 degrees in either direction. There are two products: rain rate and wind speed.

The basis of the HIRAD design is the Stepped Frequency Microwave Radiometer (SFMR) that has successfully measured surface wind speed and rain rate in hurricanes from the NOAA Hurricane Research Division’s (HRD) P-3 aircraft. Unlike the SFMR that views only at nadir, the HIRAD provides wide-swath measurements between ± 40 degrees in incidence angle with a spot-beam spatial resolution of approximately 1-3 km. HIRAD would be able to provide high resolution hurricane imaging when used on an operational hurricane surveillance aircraft such as the NOAA HRD’s Gulfstream-IV.

Measures concentration and records images of cloud particles from approximately 50-1600 microns in diameter with a resolution of 25 microns per pixel. Measures cloud droplet and aerosol concentrations within the size range of 0.5-50 microns.

The three DMT instruments included in the CAPS are the Cloud Imaging Probe (CIP), the Cloud and Aerosol Spectrometer (CAS), and the Hotwire Liquid Water Content Sensor (Hotwire LWC).

The CIP, which measures larger particles, operates as follows. Shadow images of particles passing through a collimated laser beam are projected onto a linear array of 64 photodetectors. The presence of a particle is registered by a change in the light level on each diode. The registered changes in the photodetectors are stored at a rate consistent with probe velocity and the instrument’s size resolution. Particle images are reconstructed from individual “slices,” where a slice is the state of the 64-element linear array at a given moment in time. A slice must be stored each time interval that the particle advances through the beam a distance equal to the resolution of the probe. Optional grayscale imaging gives three levels of shadow recording on each photodetector, allowing more detailed information on the particles.

The CAS, which measures smaller particles, relies on light-scattering rather than imaging techniques. Particles scatter light from an incident laser, and collecting optics guide the light scattered in the 4° to 12° range into a forward-sizing photodetector. This light is measured and used to infer particle size. Backscatter optics also measure light in the 168° to 176° range, which allows determination of the real component of a particle’s refractive index for spherical particles.

The Hotwire LWC instrument estimates liquid water content using a heated sensing coil. The system maintains the coil at a constant temperature, usually 125 °C, and measures the power necessary to maintain this temperature. More power is needed to maintain the temperature as droplets evaporate on the coil surface and cool the surface and surrounding air. Hence, this power reading can be used to estimate LWC. Both the LWC design and the optional PADS software contain features to ensure the LWC reading is not affected by conductive heat loss.

The Harvard Herriott Hygrometer (HHH) is a multipass Herriott cell that measures water vapor via direct detection. Predicted accuracy and precision are ± 3–5% and ± 0.05 ppmv H2O, in the lower stratosphere, for a 10-s integration time, respectively. The theory and application of HHH as a water vapor instrument are laid out in the context of making accurate measurements traceable to laboratory standards. In conjunction with the Harvard Water Vapor (HWV) instrument, HHH will establish ultimate credibility via three, independent detection methods in-flight and five for laboratory and in-field calibration. A multi-detection, calibration system of this nature is beyond the scope of any in existence today. Because HHH promises such high reliability and slight margins of error, the data acquired by this instrument should minimize the uncertainty associated with natural and anthropogenic climate forcing. HHH may serve as a prototype instrument for the use of miniaturized, TDL systems as in situ quantifiers of atmospheric gases via the straightforward method of direct detection, thus extending the scientific payback of this new system.

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)