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  • 1
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    Atmospheric lifetime and annual release estimates for CFCl3 and CF2Cl2 from 5 years of ALE data (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: CFCl3 and CF2Cl2 data for the 5-year period from July 1978-June 1983 are analyzed. The lifetime estimates are updated using the trend technique and the annual global release rates of the gases are derived. The effects of release uncertainties on lifetime estimates are examined by studying fluorocarbon data. It is observed that in 1981 the mixing ratios for CFCl3 and CF2Cl2 displayed increases of 8.8. and 15.3 pptv/year respectively, and the trend lifetime for CFCl13 is 74 + 31 or - 17 years and for CF2Cl2 111 + 222 or - 44 years.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 10797-10
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  • 2
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    Causes of increasing atmospheric methane - Depletion of hydroxyl radicals and the rise of emissions (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A combination of anthropogenic activities and a possible decline of global concentrations for the hydroxyl radicals that formerly removed methane from the atmosphere are cited as potential causes for the 1.3 percent/year rise of atmospheric methane levels. Calculations are presented which show that much of the methane increase over the last 200 years is probably to be divided among the two main sources in the proportions of 70 percent for anthropogenic generation and 30 percent for hydroxyl radical depletion. It is projected that in 20 years, average tropospheric concentrations of methane may be about 20 percent greater than 1980 levels. The current abundance of hydroxyl radicals may be 20 percent less than two centuries ago.
    Keywords: GEOPHYSICS
    Type: Atmospheric Environment (ISSN 0004-6981); 19; 397-407
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  • 3
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    The Atmospheric Lifetime Experiment. II - Calibration (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The calibration standards used in the Atmospheric Lifetime Experiment (ALE) for CFCl3, CF2Cl2, CH3CCl3, and CCl4 are described. This includes the preparation of the primary standards by static dilution and their propagation and stability for the period 1977-1982. Two independent assessments of the absolute concentrations of the primary standards used to initiate the ALE measurements in 1977-1978 are reported. For consistency in the ALE program the values assigned to the primary standards and subsequent working standards used in the field were not altered during the experiment when results of better estimates of the original concentration values were obtained. Rather, the appropriate factors by which the ALE mixing ratios for a given species should be multiplied to obtain the best estimate of the current concentration of a given species, are provided.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 20
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  • 4
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    The atmospheric lifetime experiment. III - Lifetime methodology and application to three years of CFCL3 data (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of the chlorofluorocarbon CFCl3 obtained several times daily over the period July 1978 to June 1981 at Adrigole, Ireland; Ragged Point, Barbados; Point Matatula, American Samoa; and Cape Grim, Tasmania are reported. In addition, observations at Cape Meares, Oregon are given for the period January 1980 to June 1981. On January 1, 1980, the average mixing ratio of CFCl3 in the lower troposphere is esimated to have been 168 pptv, and this is calculated to have been increasing 5.7 percent annually. Assuming that the only destruction of CFCl3 occurs in the stratosphere, the lifetime, on January 1, 1980, estimated by a trend technique is 83 + 73, or -27 years; the lifetime estimated from the global inventory of CFCl3 is to + 89 or -25 years. The maximum likelihood current lifetime estimate obtained by combining the estimates from both analysis techniques is 78 years.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 20
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  • 5
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    The atmospheric lifetime experiment. I - Introduction, instrumentation, and overview (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The Atmospheric Lifetime Experiment is designed to determine accurately the atmospheric concentrations of the four halocarbons CFCl3, CF2Cl2, CCl4, and CH3CCl3, and also of N2O with emphasis on measurement of their long-term trends in the atmosphere. Comparison of these concentrations and trends for the four halocarbons with estimates of their industrial emission rates then enables calculations of their global circulation rates and globally averaged atmospheric lifetimes. The experiment utilizes automated dual-column electron-capture gas chromatographs which sample the background air about 4 times daily at the following globally distributed sites: Adrigole, Ireland, Cape Meares, Oregon; Ragged Point, Barbados; Point Matatula, American Samoa, and Cape Grim, Tasmania. The climatology of these 'clean air' sites and their ability to describe the global air mass are reviewed. The instrumentation and methods for data acquisition and processing are then described. An overview of the data obtained and the trends derived during the 3-year period from July 1978 through June 1981 for each of the five species being measured is presented.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 20
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  • 6
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    The Atmospheric Lifetime Experiment. IV - Results for CF2Cl2 based on three years data (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Observations of dichlorodifluoromethane obtained several times daily over the period July 1978 to June 1981 at Adrigole, Ireland (52 deg N, 10 deg W), Ragged Point, Barbados (13 deg N, 59 deg W), Point Matatula, American Samoa (14 deg S, 171 deg W), and Cape Grim, Tasmania (41 deg S, 145 deg E), are reported. Observations at Cape Meares, Oregon (45 deg N, 124 deg W), are also given for the period November 1980 to June 1981. On January 1, 1980, the average mixing ratio of dichlorodifluoromethane in the lower troposphere is estimated to have been 285 pptv and to have been increasing at 6.0 percent/year. The atmospheric lifetime of this compound is estimated from this data by adjusting its destruction rate in a two-dimensional model of the atmosphere so as to provide the best fit to the observations. Assuming destruction of CF2Cl2 in the stratosphere only, the lifetime estimate for January 1, 1980, by the inventory technique is 69 + 36 or - 18 years. The trend technique principally provides a lower limit to the lifetime of 81 years. The results suggest a need for further assessment of dichlorodifluoromethane release estimates, particularly those from the USSR and eastern Europe.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 20
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  • 7
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    Air chemistry over the tropical forest of Guyana (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A comparison is made of the atmospheric chemistry within and above the atmospheric boundary layer over the tropical forest of Guyana. The data were gathered by NASA during the Global Tropospheric Experiment program in 1984, with an instrumented aircraft being used to collect data at altitudes of 3.5 km and between 150-450 m. The synoptic data covered concentrations of O3, CO, dimethylsulfide (DMS), halocarbons and isoprene and three different aerosol particulate measurements (DIAL system). The forest boundary layer proved to be a significant sink for O3, and a source for substantial emissions of DMS. Isoprene emitted by the forest was photochemically oxidized and became a source of CO.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 8603-861
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  • 8
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    Highly Autonomous Systems Workshop (1998)
    In:  Other Sources
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    Publication Date: 2018-06-08
    Description: It is our aim by launching a series of workshops on the topic of highly autonomous systems to reach out to the larger community interested in technology development for remotely deployed systems, particularly those for exploration.
    Keywords: Cybernetics, Artificial Intelligence and Robotics
    Type: American Association for Artificial Intelligence; United States
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  • 9
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    Increase and seasonal cycles of nitrous oxide in the earth's atmosphere (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is determined that nitrous oxide (N2O) is increasing at about 0.9 ppb/yr in the northern hemisphere and at about 0.7 ppb/yr in the southern hemisphere, based on about 9000 ground-level measurements at Cape Meares, Oregon (45 deg N), and Cape Grim, Tasmania (42 deg S), spanning a three-year period. It is also shown that the N2O concentrations vary with season in the northern hemisphere, where the concentrations are 0.8 ppbv higher during April, May, and June compared to the rest of the year, and in the southern hemisphere where the concentrations are about 0.5 ppbv lower during March, April, and May compared to the rest of the year. An explanation of this increase as a sizeable anthropogenically-controlled land-based source is presented, based on an examination of the existing estimates of natural and anthropogenic sources of N2O. Mass-balance calculations are also presented which suggest that a natural land-based source, peaking in spring, would explain the main features of the observed seasonal cycle. A growth model is employed to extrapolate the observed increase of N2O into the future and the results are compared with exponential extrapolations.
    Keywords: GEOPHYSICS
    Type: Tellus, Series B - Chemical and Physical Meteorology (ISSN 0280-6509); 35B; July 198
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  • 10
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    Sources, sinks, and seasonal cycles of atmospheric methane (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; June 20
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