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Improve measurements of key atmospheric constituents and parametersESSL provides the community with proven instrumentation and data for a wide range of applications. Increased interdisciplinary and multidisciplinary activities are driving the need to enhance our measurement capabilities. To continue to push the frontier of experimental science it is imperative that ESSL scientists and researches, in conjunction with our university and federal agency collaborators, design, develop, and implement new instrumentation. In particular, ESSL will improve measurements of key atmospheric constituents and parameters; develop a one-meter aperture coronagraph, enhance the use of space-based remote sensing data and develop new space-based instrumentation. HIAPER instrumentation [Highlight] - ACD HIAPER instrumentation
A portion of the funds awarded for the HIAPER project was earmarked for the development of instrumentation for this new research platform. NSF solicited proposals through the NSF HIAPER Aircraft Instrumentation Solicitation (HAIS). NSF oversaw the solicitation of proposals and also had responsibility for the proposal review process and the making of final award decisions. In August 2004, NCAR announced NSF's decisions regarding awards for the development of HIAPER instrumentation. ACD scientists are PIs or co-PIs on four of these awards. PI: Rick Shetter (UCAR/NCAR) Estimated Completion: 2006HIAPER Atmospheric Radiation Package (HARP) - Spectrally resolved actinic flux measurements and spectroradiometric actinic flux and irradiance measurements. Shetter and three co-investigators, Barry Lefer (University of Houston), Manfred Wendisch (Leibniz Institute for Tropospheric Research, Germany), and Peter Pilewski (CU), will provide state-of-the-art radiation instrumentation for the HIAPER aircraft. The instruments include down and up-welling wavelength dependent actinic flux spectroradiometers and down and up-welling horizontally stabilized wavelength dependent irradiance spectroradiometers. The actinic flux spectroradiometers will provide actinic flux data from 280 to 680 nm with data frequencies ranging from 0.1 to 10 Hz. The irradiance instruments will provide flat plate irradiance from 300 to 2400 nm with data frequencies of 1 Hz. The irradiance optical collectors will be mounted on actively stabilized platforms to maintain horizontal stability to 0.1 degree up to aircraft pitch and roll angles of 6 degrees. The instrument design has been approved and fabrication is ongoing. FY2007 work will include finalizing fabrication and installing the instrument on the GV for test flights. PI: Teresa Campos (UCAR/NCAR) Estimated Completion: 2006Fast Ozone Instrument - Quantification of ozone mixing ratios at 5 Hz using the method of chemiluminescent reaction of ozone with nitric oxide. A preliminary instrument package constructed in FY2006 by ACD scientists included a previously flown detection unit and some components designed and certified as part of the HAIS O 3 instrument development. This fast ozone instrument was deployed on the GV during the T-REX campaign. The FY 2007 plan for the HAIS fast-ozone project is to develop techniques for frequency-response testing and to conduct tests on an old module. This will facilitate design and testing of the 5-Hz HAIS detection module which will be built for delivery by the end of FY 07. Two components of the HAIS system, (1) a NO containment vessel and (2) the data-acquisition-system/power-supply, have already been built, certified, and flown, and will be flown in FY07 in support of an old detection module during ICE-L and PASE on the C-130 and possibly on the GV during PACDEX. This group also provided CO and H2O vapor instruments during the first G-V missions, prior to delivery and validation of their HAIS counterparts. The water instrument is a 2-channel open path laser hygrometer, with a 1 ppmv lower limit of detection, and the CO measurement is based on VUV resonance fluorescence. Though both were commercial purchases, both have been modified: the hygrometer software was modified to improve accuracy and CO was modified to allow high altitude operation. PI: Eric Apel (UCAR/NCAR) Estimated Completion: 2008Trace Organic Gas Analyzer (TOGA) - In situ measurements of oxygenated volatile organic compounds (OVOCs), non-methane hydrocarbons (NMHCs), and halocarbons. The TOGA will have the unique capability of simultaneously measuring, with one instrument, a suite of organic compounds that play important functions in many areas of atmospheric chemistry. Several of the compounds are precursors or intermediates in atmospheric oxidation sequences. Others are indicators or tracers of different anthropogenic and biogenic processes. The compounds that TOGA will measure consist of a series of hydrocarbons, oxygenated compounds, halocarbons (including HCFCs and CFCs), and a few nitrogen and sulfur containing compounds. These species are identified in the HIAPER Advisory Committee Report as high priority. These measurements are possible due to the very recent development of new fast gas chromatographs. A prototype of this instrument was flown on the NSF/NCAR C-130 during MIRAGE and INTEX-B. This instrument is currently undergoing design review. FY2007 plans are to complete the design review and begin fabrication of the instrument. PI: Greg Huey (Georgia Institute of Technology), CoPI David Hanson Estimated Completion: 2007Chemical Ionization Mass Spectrometer (CIMS) - Measurements of nitric acid, pernitric acid, and sulfur dioxide in standard CIMS (negative ion) mode, and measurements of organics such as methanol, acetaldehyde, acetonitrile, and acetone in CIMS positive ion mode. A CIMS capable of measurements in two basic configurations will be constructed for HIAPER. In one configuration the instrument will measure nitric acid, pernitric acid, and sulfur dioxide in real time. Other species such as chlorine nitrate and dinitrogen pentoxide may be available after post-flight data processing. The second configuration will allow measurements of organic compounds such as methanol, acetaldehyde, and acetone. Data will be reported from one to three second time intervals. FY 2007 plans are to complete the design review and begin fabrication. ACD scientists are also involved with design and fabrication of additional instruments designed for HIAPER. A major effort has continued with the design, fabrication, and laboratory testing of components for the HIAPER NO y /NO instrument. The basic detector module, electronics, data system design and much of the machining have been completed. Assembly is ongoing and testing will start in December. The design of inlets and fabrication has yet to be completed. In addition, a new, compact mass spectrometer instrument has been designed and built that is four to five times smaller and lighter than the existing four-channel system but still provides similar sensitivity for measuring OH, H2SO4 and MSA. The new system makes use of advances in mass spectrometer and octopole lens design and will serve as a prototype for a future HIAPER OH instrument. Finally, ACD scientists developed a compact (within the limits of long internal path length) high resolution (0.003 cm-1) Fourier transform spectrometer for use aboard HIAPER. The optics and mechanical components of that instrument were completed and tested and electronics are in production.
Atmospheric chemistry instrumentation
ACD scientists are involved in ongoing efforts to develop, improve, operate, and maintain a number of instruments designed to measure trace gases, radicals, optical properties, and aerosols in the atmosphere. A number of instruments measure trace gases and radicals that are required for studies of photochemistry including O3, NOx, NOy, PANs, HOx, RO2, H2SO4, HNO3, and NH3. Ozone, NOx, and NOy are measured by by chemiluminescence instruments . The remaining species are measured by chemical ionization mass spectroscopy (CIMS) techniques. The NH3 measurement is a recent addition and was used in the field for the first time this year. This technique involved the ionization of the sample flow in which the velocity had been slowed by a factor of 2 from that of the free steam aircraft. This ionization was achieved via a stainless steel corona needle with a 3-4 kV potential applied. Once formed these ions were then directed via electrostatic lenses into a quadrupole mass spectrometer for detection. All of these instruments flew on the NSF/NCAR C-130 during MIRAGE and INTEX-B. Many of them have also been used on other aircraft and in ground based studies. Another set of instruments use optical techniques for measurement of actinic flux and column measurements of a number of gases. The Scanning Actinic Flux Spectroradiometer (SAFS) instruments determine wavelength dependent actinic flux from 280-420 nm. The aircraft instrument package includes two independent, but time synchronized (IRIG-B) spectroradiometer systems to measure the up- and down-welling fluxes in a 10 second scan time. Summing these produced the spherically integrated actinic flux. The actinic flux measurements in combination with the absorption cross section and quantum yield molecular data are used to calculate in situ photolysis of 23 important photochemical species, including O3, NO2, HONO, CH2O, H2O2, CH3OOH, HNO3, PAN, CH3NO3, CH3CH2NO3, and CH3COCH3. The Solid state, CCD Actinic Flux Spectroradiometers (CAFS) instruments were deployed successfully on the NASA WB-57 Costa Rica Aura Validation Experiment (CR-AVE). The CAFS measurements of up and downwelling flux were used in conjunction with radiative transfer calculations to obtain the direct solar beam fraction of the measured flux as a function of wavelength. The ozone absorption of the direct beam was determined to obtain the total ozone column abundances above the aircraft. During MIRAGE, ground based column measurements of a number of gases of interest in an urban plume environment, including CO, H 2 O, NH 3 and C 2 H 4 were made using a .06cm -1 resolution Fourier transform spectrometer. High resolution spectra of atmospheric infrared absorption were recorded and infrared spectra were fit to retrieve column amounts, and some vertical profiles. ACD scientists, in collaboration with researchers from the Georgia Institute of Technology, have also developed instruments to address the need for atmospheric measurements that elucidate aerosol-cloud-climate interactions. Ultrafine aerosols from a variety of sources, including those generated from urban air pollution as well as naturally from plant emissions, possess the ability to form cloud droplets through the uptake of water in supersaturated air. This ability for ultrafine aerosols to form cloud droplets depends ultimately on their chemical composition and size. A suite of instruments were developed to study the effects of ultrafine aerosol chemical composition on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. Three essential elements to this suite are instruments that measure hygroscopicity (uptake of water onto particles that are exposed to air at 90% Relative Humidity), CCN concentration (fraction of particles that activate into cloud droplets when exposed to a supersaturation of water in air), and particle chemical composition using Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Another suite of instruments have been developed to measure organic compounds from aircraft and ground based sites. The aircraft instruments are based on gas chromatography/mass spectrometry and proton transfer mass spectrometry and were designed to measure key organic compounds, including VOCs, in-situ , with high accuracy and precision. Both instruments were flown on the NSF/NCAR C-130 during MIRAGE and INTEX-B. Ground based systems are designed to measure fluxes of key organic compounds, including isoprene, from towers and tethered balloons. Analytical systems for these measurements are based on gas chromatography/mass spectrometry and gas chromatography/flame ionization detection.
Instrument and experimental meteorology
In the late 1980’s, in-situ measurements of cirrus-cloud ice-particle-size distributions were compared to retrievals of ice-cloud particle sizes from Landsat radiance measurements. The retrieved sizes were a factor of two to three smaller than measured, leading researchers to speculate that under-measurement of the concentrations of small ice crystals by in-situ probes was the cause of this discrepancy. However, upon closer examination, measurement of the concentrations of sub-100 micron ice particles by were found to be overestimated, by a factor of two or more. Although crucial for radiative transfer and cloud process and modeling studies, the cloud physics community cannot confidently measure the concentrations of particles smaller than about 100 µ m. For this reason, NCAR scientists have worked toward acquiring a new type of probe that has been designed to reduce known problems with the earlier probes. The small ice detector (SID-2) probe, developed by Prof. Paul Kaye of the University of Hertfordshire in England, will be brought to NCAR through funding from the NSF HIAPER Aircraft Development Process. The SID-2 will measure droplet-size distributions, differentiate droplets from ice particles, determine their respective concentrations, and determine characteristics of the shape of each of the sampled particles (see Fig.). A unique part of this instrument is its ability to detect scattering at multiple angles. The SID-2 is scheduled to be completed for HIAPER in late 2006. It will first participate in the ice in clouds (ICE) layer cloud experiment in March 2007, then operate on the HIAPER aircraft during the Pacific Dust Experiment (PACDEX) in May or June, 2007. In preparation for participation in these experiments, software development is underway and instrument testing and evaluations are in the planning stages. This work is supported by NSF and the NSF HIAS initiative. Laboratory experimentation Some aspects of the processes of cloud glaciation and the microphysics of precipitation formation are best studied in the laboratory, and these studies are pursued in ESSL's MMM division. Laboratory experimentation includes an assorted group of projects that changes from year to year. Accomplishments in fiscal year 2006 consisted of publication of studies of ice nucleation and growth carried out in the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) cloud chamber in Karlsruhe, Germany by ESSL/MMM scientists and collaborators, and measurements taken in that chamber; an experimental study of ice spikes, carried out in the cold room; and, work on giant hailstones from the Aurora, Colorado hailstorm (published in FY06), and a study of some unique hailstones from a storm in Boulder on June 24, 2006.
The large, low-temperature, expansion AIDA cloud chamber in Karlsruhe is particularly well suited for studying ice formation and crystal growth in cirrus cloud conditions; in the case illustrated here, using Sahara dust as ice nuclei. It is also an excellent platform for instrument intercomparison, and all of these objectives are pursued simultaneously. These studies have been revealing new features of ice nucleation, one of which is illustrated in the accompanying figure, as well as providing data for evaluating the importance of natural sources of ice nuclei for the formation of long-lasting cirrus clouds. The other experimental projects concerned ice spikes and aspects of hailstone formation. The giant hailstones from the Aurora hailstorm revealed a great amount of wet growth as well as a very convoluted lobe structure that may be unique to the largest hailstones. The Boulder storm on June 24, 2006 produced large quantities of very low density hail that fell to the ground mostly as slush; as far as we know this has not been reported previously. It also produced soft, golf-ball-sized hail with shapes and internal structures that also are unique, and since a good collection was made there is an opportunity to extend the knowledge of hailstone formation. Future laboratory experiments addressing ice nucleation/growth and the microphysics of percipitation will be carried out as time and NSF funding permits.
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