|ClO/BrO||Multiple Axis Resonance Fluorescence Chemical Conversion Detector for ClO and BrO||Vacuum ultraviolet radiation produced in a low pressure plasma discharge lamp is used to induce resonance scattering in Cl and Br atoms within a flowing sample. ClO and BrO are converted to Cl and Br by the addition of NO such that the rapid bimolecular reaction ClO + NO → Cl + NO2 (BrO + NO → Br + NO2) yields one halogen atom for each halogen oxide radical present in the flowing sample. Three detection axes are used to diagnose the spatial (and thus temporal) dependence of the ClO (BrO) to Cl (Br) conversion and to detect any removal of Cl (Br) following its formation. A double duct system is used both to maintain laminar flow through the detection region and to step the flow velocity in the detection region down from free stream (200 m/sec) to 20 m/sec in order to optimize the kinetic diagnosis.||James Anderson||Harvard University|
|MMS||Meteorological Measurement System||State-of-the-art instrument for measuring accurate, high resolution in situ airborne state parameters (pressure, temperature, turbulence index, and the 3-dimensional wind vector). These key measurements enable our understanding of atmospheric dynamics, chemistry and microphysical processes. The MMS is used to investigate atmospheric mesoscale (gravity and mountain lee waves) and microscale (turbulence) phenomena. An accurate characterization of the turbulence phenomenon is important for the understanding of dynamic processes in the atmosphere, such as the behavior of buoyant plumes within cirrus clouds, diffusions of chemical species within wake vortices generated by jet aircraft, and microphysical processes in breaking gravity waves. Accurate temperature and pressure data are needed to evaluate chemical reaction rates as well as to determine accurate mixing ratios. Accurate wind field data establish a detailed relationship with the various constituents and the measured wind also verifies numerical models used to evaluate air mass origin. Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.||Roland Chan||NASA Ames|
|NOy||NOy Detector||Has three independent chemiluminescence detectors for simultaneous measurements of NOy, NO2, and NO. Each detector utilizes the reaction between NO in the sample with reagent O3. The NO/O3 reaction produces excited state NO2 which emits light of near 1µm wavelength. Emitted photons are detected with a cooled photomultiplier tube.|
Because NOy species other than NO do not respond in the chemiluminescence detector, NOy component species are reduced to NO by catalytic reduction on a gold surface with carbon monoxide (CO) acting as a reducing agent. Conversion efficiencies are > 90% at surface temperatures of 300°C. An NO signal representing NOy is then detected by chemiluminescence in the detector module. The catalyst is located outside the aircraft fuselage in order to avoid inlet line losses. NO2 is photolytically converted to NO in a glass cell in the presence of intense UV light between 300 and 400 nm. The conversion fraction is > 50% for a residence time of 1 s. The chemiluminescence detector detects NO as well as the additional NO from NO2. The third channel measures NO directly by passing the ambient sample through the detector module.
The response of each detector is checked several times in flight by standard addition of NO or NO2 calibration gas. The baseline of each measurement is determined in part by the addition of synthetic air that contains no reactive nitrogen. A continuous flow of water vapor is added directly to the sample flow in order to reduce the background signal in the detectors.
The sampling inlet for NOy is located outside the fuselage of the aircraft in a separate football-shaped housing. The shape of the housing allows for the inertial separation of large aerosols (> 5 µm diameter) from the NOy inlet at the downstream end of the housing.
|David Fahey||NOAA Aeronomy Lab|
|FPCAS||Forward Scattering Spectrometer Probe (FSSP) Model 300 Aerosol Spectrometer||The aerosol size spectrometers size particles by measuring the amount of laser light scattered from angles of 4 to 12° by aerosol particles in situ as they pass through a focused laser beam. Comparison of voltage outputs from the signal detector and a masked slit detector is used to electro-optically define the sample area. Instrument system is composed of two parts: (1) a Particle Measuring Systems model FSSP-300 aerosol spectrometer, and (2) a data acquisition and recording system. The FSSP-300 aerosol spectrometer is located on the front of the starboard spear pod of the ER-2. The data acquisition and recording system is part of the package that houses the FPCAS aerosol spectrometer located in the bottom, rear portion of the pod. The FSSP-300 aerosol spectrometer sizes particles in the 0.4 to 20 micron diameter size range (depending on the refractive index of the aerosol particles measured) in the free air stream outside the ER-2. The measured particles are divided into 31 size intervals with more resolution at smaller sizes.|
Detection Limit: 0.4 to 20 micrometers diameter, Sampling Rate: 0.1 Hertz
|Guy V. Ferry||NASA Ames|
|EA/ET||ER-2 altitude profiles and flight track||Steve Gaines||NASA Ames|
|MFS||Multi-Filter Sampler||Designed to measure aerosols and gases in the stratosphere by collection on a filter system. Cycles filters in and out of the airstream and isolates the sampled as well as the unsampled filters from contamination. The sampler is operated by the pilot, with automatic sequencing of a filter into position from a single switch position change in the cockpit. The air flow is measured with a propeller anemometer. The air temperature, pressure, flow and instrument diagnostics are recorded with an on board data acquisition system.|
After a flight, the filters are extracted with an aqueous solution containing a wetting agent. The solution is analyzed by Ion Chromatography to determine the amounts of each ion collected.
Filter samples were obtained for the determination of the total nitrate, sulfate, acidic chloride and acidic fluoride content along the flight path of the NASA ER-2. On three flights of the 12-flight series, filters were flown that allowed the separate but simultaneous collection of these species in the aerosol and vapor phase.
|MTP||Microwave Temperature Profiler||A passive microwave radiometer which measures the natural thermal emission from oxygen molecules in the earth’s atmosphere for a selection of elevation angles between zenith and nadir. The current observing frequencies are 55.51, 56.65 and 58.80 GHz. The measured "brightness temperatures" versus elevation angle are converted to air temperature versus altitude using a quasi-Bayesian statistical retrieval procedure. The MTP has no ITAR restrictions, has export compliance classification number EAR99/NLR. An MTP generally consists of two assemblies: a sensor unit (SU), which receives and detects the signal, and a data unit (DU), which controls the SU and records the data. In addition, on some platforms there may be a third element, a real-time analysis computer (RAC), which analyzes the data to produce temperature profiles and other data products in real time. The SU is connected to the DU with power, control, and data cables. In addition the DU has interfaces to the aircraft navigation data bus and the RAC, if one is present. Navigation data is needed so that information such as altitude, pitch and roll are available. Aircraft altitude is needed to perform retrievals (which are altitude dependent), while pitch and roll are needed for controlling the position of a stepper motor which must drive a scanning mirror to predetermined elevation angles. Generally, the feed horn is nearly normal to the flight direction and the scanning mirror is oriented at 45-degrees with respect to receiving feed horn to allow viewing from near nadir to near zenith. At each viewing position a local oscillator (LO) is sequenced through two or more frequencies. Since a double sideband receiver is used, the LO is generally located near the "valley" between two spectral lines, so that the upper and lower sidebands are located near the spectral line peaks to ensure the maximum absorption. This is especially important at high altitudes where "transparency" corrections become important if the lines are too "thin." Because each frequency has a different effective viewing distance, the MTP is able to "see" to different distances by changing frequency. In addition, because the viewing direction is also varied and because the atmospheric opacity is temperature and pressure dependent, different effective viewing distances are also achieved through scanning in elevation . If the scanning is done so that the applicable altitudes (that is, the effective viewing distance times the sine of the elevation angle) at different frequencies and elevation angles are the same, then inter-frequency calibration can also be done, which improves the quality of the retrieved profiles. For a two-frequency radiometer with 10 elevation angles, each 15-second observing cycle produces a set of 20 brightness temperatures, which are converted by a linear retrieval algorithm to a profile of air temperature versus altitude, T(z). Finally, radiometric calibration is performed using the outside air temperature (OAT) and a heated reference target to determine the instrument gain. However, complete calibration of the system to include "window corrections" and other effects, requires tedious analysis and comparison with radiosondes near the aircraft flight path. This is probably the most important single factor contributing to reliable calibration. For stable MTPs, like that on the DC8, such calibrations appear to be reliable for many years. Such analysis is always performed before MTP data are placed on mission archive computers.||Bruce Gary||JPL|
|WAS||Whole Air Sampler||Collects samples from airborne platforms for detailed analysis of a wide range of trace gases. The compounds that are typically measured from the WAS include trace gases with sources from industrial midlatitude emissions, from biomass burning, and from the marine boundary layer, with certain compounds (e.g. organic nitrates) that have a unique source in the equatorial surface ocean. The use of a broad suite of tracers with different sources and lifetimes provides powerful diagnostic information on air mass history and chemical processing that currently is only available from measurements from whole air samples. Previous deployments of the whole air sampler have shown that the sampling and analytical procedures employed by our group are capable of accessing the wide range of mixing ratios at sufficient precision to be used for tracer studies. Thus, routine measurement of species, such as methyl iodide, at <= 0.1 x 10-12 mole fraction, or NMHC at levels of a few x 10-12 mole fraction are possible. In addition to the tracer aspects of the whole air sampler measurements, we measure a full suite of halocarbon species that provide information on the role of short-lived halocarbons in the tropical UT/LS region, on halogen budgets in the UT/LS region, and on continuing increasing temporal trends of HFCs (such as 134a), HCFCs (such as HCFC 141b), PFCs (such as C2F6), as well as declining levels of some of the major CFCs and halogenated solvents. The measurements of those species that are changing rapidly in the troposphere also give direct indications of the age and origin of air entering the stratosphere.||Leroy Heidt|
|WV||Water Vapor||Total water is measured in situ as vapor with a Lyman-Alpha hygrometer. High ambient sample flows through a closed cell minimize the effect of trapped water. Lyman-alpha light (121.6 nm) photodissociates water to produce an excited OH radical. The fluorescence from this radical at 309 nm is detected with a phototube and counting system. At aircraft pressures the fluorescence signal is quenched by air which gives a signal that is proportional to mixing ratio. The Lyman-Alpha radiation produced with a DC-discharge lamp is monitored with an iodine ionization cell that is sensitive from 115 nm to 135 nm. Calibration occurs in flight by injecting water vapor directly into the ambient sample flow.||Ken Kelly||NOAA Aeronomy Lab|
|ATLAS||Airborne Tunable Laser Absorption Spectrometer||ATLAS uses a tunable laser to detect an infrared-active target gas such as N2O, methane, carbon monoxide, or ozone. The laser source is tuned to an individual roto-vibrational line in an infrared absorption band of the target gas, and is frequency modulated at 2 kHz. The instrument detects the infrared target gas by measuring the fractional absorption of the infrared beam from the tunable diode laser as it traverses a multipass White cell containing an atmospheric sample at ambient pressure.|
Synchronous detection of the resultant amplitude modulation at 2kHz and 4kHz yields the first and second harmonics of the generally weak absorption feature with high sensitivity (DI/I < 1E-5). Part of the main beam is split off through a short cell containing a known amount of the target gas to a reference detector. The reference first harmonic signal is used to lock the laser frequency to the absorption line center, while the second harmonic signal is used to derive the calibration factor needed to convert the measurement beam second harmonic amplitude into absolute gas concentration. A zero beam is included to correct for background gas absorption occurring outside the multipass cell. The response time of the instrument is set by the gas flow rate through the White cell, which is normally adjusted to give a new sample every second. Periodic standard additions of the target gas are injected into the sample stream as a second method to calibrate the measurement technique and as an overall instrument diagnostic.
|O3||Dual-Beam UV-Absorption Ozone Photometer||Consists of a mercury lamp, two sample chambers that can be periodically scrubbed of ozone, and two detectors that measure the 254-nm radiation transmitted through the chamber. The ozone absorption cross-section at this wavelength is accurately known; hence, the ozone number density can be easily calculated. Since the two absorption chambers are identical, virtually continuous measurements of ozone are made by alternating the ambient air sample and ozone scrubbed sample between the two chambers. At a one-second data collection rate, the minimum detectable concentration of ozone (one standard deviation) is 1.5 x 10 10 molecules/cm 3 (0.6ppbv at STP).||Mike Proffitt||NOAA Aeronomy Lab|
|UOP||Ultraviolet Ozone Photometer||Determines the amount of ozone in sampled air by measuring the transmission of UV radiation through a known pathlength of air with and without ozone present. The pressure and temperature of the sampled air, which flows continuously through the instrument, are also measured. Ultraviolet radiation of 253.7 nm generated by a mercury lamp is utilized. This radiation lies almost exactly at the wavelength of maximum near-UV absorption by ozone. By suitable choice of filters and radiation detectors, essentially all the measured radiation is from this single mercury line for which an accurate value of the absorption coefficient is known. These measurements together with the absorption coefficient yield the atmospheric ozone mixing ratio.||Walter Starr||NASA Ames|
|CNC||Condensation Nucleus Counter||Developed for use on NASA high altitude aircraft and measures the number concentration of aerosol particles having diameters in the 0.01 to about 1.0 micron range. Operates at altitudes from 8 km - 21.5 km. Recent developments include an impactor which can be used to remove particles larger than 0.11 micron in diameter.|
The instrument functions by saturating the aerosol sample with warm alcohol vapor and then cooling the sample so that the alcohol vapor condenses on particles in the sample causing them to grow to the sizes that can easily be detected by a simple optical particle counter. Thus individual particles are counted.
|James Wilson||University of Denver|