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9 Instrument and Platform Survey BY V. MOHNEN, F. ALLARIO, D. DAVIS, D. LENSCHOW, AND R.TANNER Of central importance in our considerations of the requirements for technology development and plat- forms in any future tropospheric chemistry program were analytical techniques for the measurement of the various chemical species in the troposphere. We devel- oped an up-to-date overview of the present analytical capabilities on the basis of a request for information that was sent to over 250 atmospheric scientists. Obviously, the survey relies heavily on the response that we obtained, and no claims for completeness are made here. A similar survey on aircraft platforms was con- ducted by the Working Group for Coordination of Research Aircraft and collected by NCAR's Research Aviation Facility, who kindly made the results of the survey available to us. Information on oceanographic platforms is available from the Commander, Naval Oceanography Com- mand, NSTL Station, Bay Street, St. Louis, and we have reviewed this information. Finally, we examined the current state-of-the-art in remote sensing technology applicable to tropospheric chemistry research. The results of the instrumentation survey and information on aircraft and oceanographic platforms are presented in this chapter, as is a very brief discussion of remote sensing technology. INSTRUMENTATION FOR IN SITU MEASUREMENTS To attain the long-term goals and objectives of the Global Tropospheric Chemistry Program, sensitive 144 instrumentation will be required for both the measure- ment of chemical species in the remote troposphere and the elucidation of critical reaction mechanisms and rates in laboratory studies. Although currently available instrumentation is adequate to initiate some of the exploratory phases of major future field programs in the proposed Global Tropospheric Chemistry Program, this instrumentation is not adequate to carry out the detailed research program outlined in this report. Currently available sensors cover a broad range from low-technol- ogy, low-cost, in situ sensors with limited accuracy and sensitivity to high-technology, delicate, accurate, but costly bench-type instrumentation that still requires considerable development and intercomparison before field deployment. In addition, there are no instruments yet available for the measurement of certain critical spe- cies in the global troposphere such as HO2. While concentration measurements for most of the major species in tropospheric chemical cycles are possi- ble today within the planetary boundary layer, many of these measurements cannot be made in the free tropo- sphere, where concentrations are significantly lower. In addition, relatively few instruments are capable of mak- ing in situ measurements with a frequency greater than one measurement per second. The higher frequency of observation (better than ~ Hz) is necessary in order to obtain flux measurements with airborne platforms. Absolute calibrations, instrument intercomparisons, and other quality control procedures during all research efforts in the Global Tropospheric Chemistry Program are required. Attainment of the long-term goals of the

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INSTRUMENT AND PLATFORM SURVEY Global Tropospheric Chemistry Program depends criti- cally on the further development and careful intercali- bration of current instrumentation and the design and testing of a new generation of instrumental techniques. We recommend that a vigorous program of instrument development, testing, and intercalibration be under- taken immediately and be continued throughout the Global Tropospheric Chemistry Program. The results of our community survey of current chemical instrumentation are summarized in Tables 9.1 through 9.24. These tables list the detection technique; the sampling mode (continuous, real time (1~; continuous, integrative (2~; intermittent (3~; and remote (4~; the development status (concept developed (1~; benchtop instrument (2~; laboratory prototype available for field testing (3~; field tested or commercial instrument (4~; the detection limit; the time resolution (the time period over which the signal is observed or averaged in order to attain the stated detection limit); the estimated accuracy (the difference in the measured value versus the "true" value); precision (the repeatability under conditions of constant concentration); calibration in the field (the low- est concentrations at which test gas mixtures have been prepared for purposes of technique calibration); the weight/power requirements; the platform usage (techniques were considered as applicable for sampling on the ground, aboard ships, or on aircraft; art "all" entry implies that the technique is suitable for all three applica- tions; a technique need not have been operated or designed for all three applications in order to be desig- nated as "alley; and ir~terferertces or constraints (species, processes, or environmental conditions that cause arti- facts, positive or negative, competing or output signals, and so on; one can never tee confident that a technique is completely interference free; one can only evaluate the technique for known or suspect interferences; environ- mental constraints can present operational problems for a technique; they differ from interferences because they either limit or invalidate the applicability of the tech- nique, or change the baseline sensitivity, calibration, accuracy, or precision of the technique). Most of the above classification parameters are diffi- cult to define and, in themselves, warrant discussion. We reviewed and, in general, accepted the classification provided by the respondents of our survey. Therefore, the tables presented here do not necessarily reflect a consensus among the authors; rather the tables are a first attempt to list without ranking- a variety of tech- niques applicable to global tropospheric measurements. REMOTE SENSING TECHNOLOGY Spaceborne remote sensors could provide near-global measurements and thus offer the ultimate goal of obtain i45 ing a three-dimensional distribution of certain atmo- spheric trace constituents. We hope this approach will eventually provide the tropospheric chemistry commu- nity with the opportunity to iterate a variety of distribu- tion measurements with evolving mathematical models of the troposphere. In assessing the capability of current remote sensor technology for performing measurements in the global troposphere, we reviewed three classes of remote sensors: imaging spectroradiometers, passive remote sensors, and active remote sensors. We found that significant technological advances, both relative to the species that can be detected and spatial resolution, are necessary to satisfy the long-term needs of the Global Tropospheric Chemistry Program. Because of the sig- nificarlt potential of remote sensing technologies for any future global measurement program, we elaborated extensively on their present status and future outlook, and this reviewis presented in Appendix B. AIRCRAFT PLATFORMS There is a wide variety of aircraft platforms currently available in the United States from government, univer- sity, and private operators. A detailed compilation of the specifications and characteristics of these aircraft is pres- ently being developed by the National Center for Atmo- spheric Research (NCAR) for use in planning research programs requiring such platforms. A brief summary of research aircraft platforms in the United States is pre- .sented in Table 9.25. Much of the information in Table 9.25 was obtained from the questionnaire sent to research aircraft operators by the Working Group for Coordination of Research Aircraft (WGCRA) and col- lected by the NCAR Research Aviation Facility. NCAR has organized and stored the responses in a data bank that can be easily accessed through the NCAR com- puter from remote locations by those interested in fur- ther details. Available platforms range from simple, two-engine aircraft with limited range and space for scientific equip- ment (over 20) to long-range, four-engine turbojet and turbo-prop transports. Currently, three jet aircraft and five turbo-prop aircraft are being utilized in some aspect of tropospheric chemistry research. In some cases, the aircraft platform is available as an unmodified vehicle, and in others, as a complete aircraft measuring system often dedicated for extensive periods oftime to meteoro- logical and atmospheric chemistry studies. One present limitation is the shortage of large, well- instrumented aircraft with sufficient interior space, power, exterior mounting locations, and specialized meteorological instrumentation for extended long- range flights investigating tropospheric chemistry in the boundary layer or lower free troposphere. At present,

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146 the NCAR Electra and the NASA Electra fill that requirement. The NOAA P-3s are a possibility, although available space is limited. In general, however, we believe that the current aircraft fleet number and type are adequate to undertake the Global Tropospheric Chemistry Program, although improvements and mod- ifications to some aircraft and the meteorological support equipment aboard them will undoubtedly be necessary. OCEANOGRAPHIC PLATFORMS The Commander, Naval Oceanography Command, with the assistance of the University-National Oceano- graphic Laboratory System (UNOLS), publishes annu- ally the Oceanographic Ships Operating Schedules. If an effective national oceanographic program is to exist, efforts must be made to maximize use of existing ocean- ographic platforms, including "piggy backing" and coordinated scheduling. To accomplish this goal, the Naval Oceanography Command has developed the Oceanographic Management Information System. A subset computer file, the Research Vehicle Reference Service (RVRS), has also been established as a central- ized source of information pertaining to ship character- istics, latest operating schedules, last known positions, and points of contact for the vessel operators. Table 9.26 was compiled from information obtained through RVRS and reflects the status of oceanographic ships at academic institutions as of 1982. UNOLS coordinates scheduling of oceanographic research vessels in the United States academic fleet. In discussing the current status ofthe fleet of ships, the subpanel noted that there is no oceanographic vessel designed specifically to carry out tropospheric chemistry research or dedicated to this area of research. Therefore, oceanographic sampling platforms will be a compro- mise between the needs of the atmospheric chemistry community and the mission for which the ship was designed. Nevertheless, sufficient ship platforms are available to undertake the proposed field research at sea in the Global Tropospheric Chemistry Program, as there are currently over 30 active ships from academic institutions and 35 operated by the federal government. As with other platforms, however, local contamination can be a serious problem if careful planning is not under- taken. Because of these potential problems, the sub- panel includes the following history and summary of the past experience of scientists who made air chemical observations over the oceans. Although the earth is pre- dominantly covered with water and the seas are the primary source of heat and water vapor to the atmo- sphere, a vast majority of all air chemical observations occur overland. This is not only a result ofthe inaccessi PART II ASSESSMENTS OF CURRENT UNDERSTANDING bility of many parts ofthe world ocean, but also a result of the difficulty of making accurate observations in the presence of a ship or platform (Roll, 1965~. Atmospheric physics was incorporated into the magnetic studies of the Galileo and Carnegie from 1910 through 1927 (Wait, 1946), and the foundations of modern marine meteorol- ogy were derived from the geochemical cruise of the Meteor in 1926- 1927 (Roll, 1965~. Many of the observations of aerosol concentrations over the seas during the first halfofthe twentieth century were performed from ships of opportunity as the investi- gator traveled to scientific meetings (Parkinson, 1952; Hess, 1948; Landsberg, 1934~. Gunn (1964) replicated the atmospheric conductivity apparatus of the Carrzeg2e aboard a U. S. freighter, and Ostlund and Mason ~ 1974) studied tritium exchange over a wide range of latitudes from USNS Towle, enroute from the United States to Antarctica. During the 1960s and 1970s, ships of opportunity were used by Elliott (1976) and Hogan et al. (1972) to characterize surface aerosol concentrations over the world ocean. Elliott (1976) supplied portable aerosol detectors to the meteorological observer aboard the Glo- mar Challenger and obtained systematic aerosol observa- tions at many oceanic lo-cations not visited by scheduled ships. Hogan et al. (1973) provided similar instruments to ships' officers contacted through the meteorology and oceanography programs of the State University of New York Maritime College. Aerosol observations were accomplished synoptically by these officers, as a part of the six hourly synoptic weather observations. Meteorology, aerosols, and air chemistry have been combined with oceanography on several oceanographic cruises. Cobb and Wells (1970) studied atmospheric conductivity from NOAA ships, and Jaenicke (1974) examined not only air chemistry, but air-sea exchange of several gases from the Meteor as part of the first GEOSECS cruise. Probably the largest shipborne meteorological programs, to date, were accomplished during GATE and FGGE, and similar experiments as part of MONEX. Aerosol particle and atmospheric chemistry measure- ments at sea are difficult for several reasons. There is a large gradient in aerosol particle and gas concentration near the surface. This gradient is influenced by the pres- ence of the ship, and as the ship is constantly moving with respect to the sea, precise, simultaneous measure- ments of both concentration and height are nearly impossible. The ship itself is a strong source of every conceivable vapor and particle, and the combination of operational wind screens and forced ventilation found on every ship makes it very difficult to find uncontami- nated sampling positions. These positions also vary with wind and the ship's speed in frustratingways. Forexam

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INSTRUMENT AND PLATFORM SURVEY pie, Hogan (1981) found that, with a beam wind of greater than 30 knots, he was able to sample uncontami- nated air only from the highest observation level on USCGC No7thwir~d, and then only on the upwind por- tion of the roll. Moyers et al. (1972) discuss the contamination prob- lems associated with aerosol sampling on board ships. They describe a bow tower sampling system combined with control of the sampling by the relative wind direc- tion. This system has been utilized on a number of research vessels for atmospheric chemistry studies and has proven to be quite satisfactory for collecting uncon- taminated samples. (See, for example, Duce and Hoff- man, 1976, and Graham and Duce, 1979.) Problems with contamination indicate that in general, however, air chemistry measurements should be limited to real- time measurements as much as possible. We concluded that there appears to be no immediate need for new or additional oceanographic platforms to satisfy the needs of atmospheric chemists. The shortage of funds to operate and/or modify the platforms for dedi- cated use appears to be the main constraint for their use . . . . In tropospheric experiments. ACKNOWLEDGMENTS 147 Gunn, R. (1964~. The secular increase of the worldwide fine parti cle pollution. J. Atmos. Sci. 21: 168- 181. Hess, V. F. (1948~. On the concentration of condensation nuclei in the air over the North Atlantic. Terrestrial Magnetism and Atmo spheric Electricity 53:399-403. Hess, V. I. (1951~. Further determinations ofthe concentrations of condensation nuclei in the air over the North Atlantic.~. Geophys. Res. 56:553-556. Hogan, A. W. (1981~. Aerosol measurements over and near the South Pacific Ocean and Ross Sea. ]. Appl. Meteorol. 20:1111 1118. Hogan, A. W., A. L. Aymer, J. M. Bishop, B. W. Harlow, J. C. Klepper, and G. Lupo (1967~. Aitken nuclei observations over the North Atlantic Ocean. /. Atmos. Sci. 6:726-727. Hogan, A. W., M. H. Degani, and C. Thor (1972~. Study of maritime aerosols. Report to the U. S. Environmental Protection Agency, Division of Meteorology. Contract 70-64, 42 pp. Hogan, A. W., V. A. Mohnen, and V. J. Schaefer (1973~. Com ments on "Oceanic aerosol levels deduced from measurements of the electrical conductivity of the atmosphere." i. Atmos. Sci. 30: 1455-1460. Jaenicke, R. (1974~. Size distribution of condensation nuclei in the NE trade regime of the African coast. I. Rech. Atmos. 8: 723-733. Keafer, L. S., Jr., ed. (1982~. Tropospheric Passive Remote Sensing. NASA Publ. No. CP 2237, June 1982. Order No. N82-26637, 95 pp. Kuhlbradt, E., and J. Refer (1935~. Die meteoroligischen Metho den und das aerologische Beobachtungsmaterial wiss. Erge~onisse derAtlarltische Expedition Meteor 14:1925- 1927. Landsberg, H. (1934~. Observations of condensation nuclei in the atmosphere. Mon. Weather Rev., Dec:442-445. Landsberg, H. (1938~. Atmospheric condensation nuclei. Ergeb. We gratefully acknowledge the help from our cot-Kosm. Phys. 3:155-252. leagues who responded to our instrument survey and toLevine, J. S., and F. Allario (1982~. The global troposphere: bio ehe ad(litional requests for help and clarification. Severalgeochemical cycles, chemistry and remote sensing. Environ. Mon individuals have helped us in the preparation of this document. These include James Hoell of NASA Langley Research Center, for detailed information on NxO' instruments; iorg Mohnen of ASRC, for coordi nating the ship survey; and Byron Phillips of NCAR, for coordinating the aircraft survey. BIBLIOGRAPHY Cobb, W. E., and H. l. Wells (1970~. The electrical conductivity of oceanic air and its correlation to global atmospheric pollution. I. Atmos. Sci. 27:814-819. Duce, R. A., and G. L. Hoffman (1976~. Atmospheric vanadium transport to the ocean. Atmos. Environ. 10:989-996. Elliott, W. R. (1976~. Condensation nuclei concentrations over the Mediterranean Sea. Atmos. Environ. 10:1091-1094. Graham, W. F., and R. A. Duce (1979) Atmospheric pathways of the phosphorus cycle. Geochim. Cosmochim. Acta 43:1 195-1208. V , , itoring assessment 1:263-306. Mason, B. I. (1957~. The ocean as a source of cloud-forming nuclei. Geofis. PuraAppl. 36:148. Moyers, J. L., R. A. Duce, and G. L. Hoffman (1972~. A note on the contamination of atmospheric particulate samples collected from ships. Atmos. Environ. 6:551-556. Moyers, I. L., and R. A. Duce (1972~. Gaseous and particulate iodine in the marine atmosphere. J. Geophys. Res. 77:5229-5238. Ostlund, H. G., and A. S. Mason (1974~. Atmospheric HT and HTO, 1. Experimental procedures and tropospheric data 1968- 1972. Tellus26:91-102. Parkinson, W. C. (1952~. Note on the concentration of condensa- tion nuclei) over the western Atlantic. J. Geophys. Res. 57:314- 315. Roll, H. U. (1965~. Physics of theMarineAtmosphere. Academic, Ne York, 426 pp. Seinfeld, J. H. (1981~. Report of the NASA Working Group on Tropo- spheric Program Planning. NASA RP 1062. Wait, G. R. (19463. Some experiments relating to the electrical conductivity of the lower atmosphere. J. Wash. A cad. 36:321- 343.

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154 TABLE 9.9 H2 PART II ASSESSMENTS OF CURRENT UNDERSTANDING Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints Doped carrier ECD gas 10 ppbv 10 min 1% 30 kg, 0.5 kW None identified chromatography Mercuric oxide reduction and 10 ppbv 5 min 1 % 20 kg, 0.5 kW CO and other reducing species atomic absorption unless separated by GO or removed absorbents TABLE 9.10 OH Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints Radio carbon tracer 1 05/cm3 100 s 20 % 180 kg, 3 kW Methoxyl radical (Campbell) Short-pulse two-wavelength 106/cm3 20 min 1000 kg, 9 kW Laser-generated OH; aerosol single- photon laser- induced fluorescence fluorescence, in situ (knavish Two-photon laser-induced flue- 2.5 x 1 05/cm3 None rescence, in situ (Davis~a Two-wavelength laser-induced 106/cm3 20 min 800 kg, 11 kW Laser-generated OH; aerosol fluorescence, lidar (Wangle fluorescence Low-pressure laser-induced 106/cm3 8 min Wall loss of OH fluorescence (Hard, Rateike) 308-nm laser-induced fluores- TBD cence (McDermid) High-rep rate laser-induced 106/cm3 20 min Aerosol fluorescence fluorescence (Andersonja aDetection limit cited is for moist conditions at 1 atmosphere pressure. At 500-mbar pressure, detection limits could be 3 to 5 times lower, depending on the LIS technique employed. NOTE: TBD = to be determined.

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158 TABLE 9. ~ 7 CC13F (F 11 ) PART II ASSESSMENTS OF CURRENT UNDERSTANDING Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints ECD gas chromatography 3 pptv 15 min 0.5 To 30 kg, 0.5 kW None identified Gas chromatography NOAA 5 ppt 10 min 50 kg, 2 kW Other electron capture trace gas porous cell A column (sensitivity 2 ppt) species TABLE 9.18 CC12F2 (F12) Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints ECD gas chromatography 5 pptv 15 min 0.5 To 30 kg, 0.5 kW None identified Gas chromatography NOAA 5 ppt 10 min 50 kg, 2 kW Other electron capture trace gas porous cell A column (sensitivity 2 ppt) species TABLE 9. ~ 9 Anions (Liquid) Technique Detection Time Limit Resolution Precision Weight/Power Requirements Interferences/Constraints SO3 SO4 NO3 Chemiluminescence 5ppbm 20 kg, 1 kW Noneidentified Ion chromatography 30 ppbm 50 kg, 500 W None identified Automated calorimetric 1 ppm technique (auto analyzer) Ion chromatography 50 ppbm 50 kg, 500 W None identified Isotope dilution(IDA) 10-8 g Liquid SOL, Sr++, Ba++ scintillation Automated calorimetric technique (auto analyzer) counter needed 1 ppm Ion chromatography 100 ppbm 50 kg, 500 W SOL, Br~, can be avoided Direct UV absorption 100 ppbm 20 kg, 100 W Aromatics, Fe+ + +, can be avoided Automated calorimetric 100 ppbm technique (auto analyzer) C1 Ion chromatography 100 ppbm 50 kg, 500 W None identified Automated calorimetric 1 ppm technique (auto analyzer)

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INSTRUMENT AND PLATFORM SURVEY TABLE 9.20 Cations (Liquid) 159 Detection Time Weight/Power Technique Limit Resolution PrecisionRequirements Interferences/Constraints Ion chromatography for NH 4, 50 ppbm minutes 50 kg, 500 W None identified Na+, K+ for analysts Atomic absorption for Ca+ +, 20 ppbm minutes 50 kg, 500 W None identified MA + for analysis TABLE 9.21 Trace Metal Vapors Technique Detection Time Limit Resolution Precision Weight/Power Requirements Interferences/Constraints Activated charcoal column ~ 1 ng/m3 1 hr Noble metal adsorber Airborne mercury spectrometer 2-5 ng/m3 < 1 ng/m3 1 hr 5 kg, 300 W Collection efficiency influenced (sampler) by temperature and humidity, specific interferences are a function of analytical technique 5 kg, 300 W Collection efficiency influenced (sampler) by temperature and humidity, specific interferences are a function of analytical technique SO2

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162 TABLE 9.23 PART II ASSESSMENTS OF CURRENT UNDERSTANDING Aerosols-Physical Measurements Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints - Condensation nuclei technique D > 50 Angstroms 2 s 60 kg, 220 W (pulsating) Conc. >lOcm-3 Condensation nuclei technique D > 500 Angstroms 5 s 15 kg, 200 W (continuous) Conc > 10-2 cm-3 Electricalmobility D>32 Angstroms 2min 25 kg, 100W Conc.-size dependent Optical scattering (white light) D ~ 0.3 Em size 25 kit, 250 W Index of refraction particle particle shape Optical scattering laser cavity 0.1,um ~ D < 6 Em 20 kg, 150 W Index of refraction particle single particle shape Laser scattering 0.3 < D < 32,um 20 kg, 250 W Index of refraction particle shape Cloud and Precipitation Particles Nephelometer~integrated D >0.1,umConc. 5s 25 kg, 150W optical) > 100 cm~3 Transmissometers (long path) D > 0. 1 (path length 5 s 100 kg, 500 W dependent) Laser scattering 0.5 'em < D < 47,um 20 kg, 150 W Index of refraction particle shape Laser image (one-dimensional 10 Em < D < 300pm 20 kg, 100 W Index of refraction particle shadow) shape Laser image (one-dimensional 150,um < D < 12 20 kg, 100 W Index of refraction particle shadow) mm shape - TABLE 9.24 Cloud Condensation Nuclei Detection Time Weight/Power Technique Limit Resolution Precision Requirements Interferences/Constraints Static diffusion chamber inte- 20 cm~3 45 s 20 kg, 200 W Large insoluble particles grated light scatter detector 0.25 < SO To ~ < 2 Continuous flow diffusion 0.02 cm~3 5min 100 kg, 1500 Largeinsoluble particles chamber single-particle opti- 0. l ~ SO To ~ < 2 W cat detector Isothermal haze chamber sin- 0.02 cm~3 5 min 40 kg, 250 W Large insoluble particles ale-particle optical detector 0. O 1 < SO To <0.25

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