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  • Africa  (1)
  • stratospheric sulfur budget  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Preliminary results on nitric oxide emission from a southern African savanna ecosystem (1997)
    Springer
    Nutrient cycling in agroecosystems 48 (1997), S. 123-138 
    Details
    ISSN: 1573-0867
    Keywords: Africa ; biogenic emission ; dry season ; dynamic chamber ; forest ; grassland ; groundnut ; maize ; Miombo typesavanna ecosystem ; nitric oxide ; pulsing ; sorghum ; wet season ; Zimbabwe
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During October to December 1994, we measured diel and seasonal variability in nitric oxide (NO) exchange by a southern African savanna ecosystem (Grasslands Research Station, Marondera, Zimbabwe). A set of automated dynamic chambers was installed in three sub-sites: Miombo forest, natural grassland, and cropped soils (maize, sorghum, groundnut). The latter received a single application of commercialy available in-organic or cowdung fertilizer. The dynamic chamber system is described in detail, including correction of the resulting data for wall losses and gas-phase reactions of the NO-NO2-O3 triad. During the dry season, net vertical NO fluxes were close to the detection limit (0.44 ngN m-2s-1) regardless of vegetation type. During the transition from dry to wet season strong "pulsing" effects of the NO flux were observed: NO emissions increased by a factor of up to 60 within hours. During the wet season, NO emissions varied between the different sub-sites of the ecosystem; corresponding means are in ranking order of fertilized agricultural plots (27.2 ngN m-2 s-1), unfertilized agricultural plots (8.5 ngN m-2 s-1 ), grassland (4.4 ngN m-2 s-1 ), and Miombo forest (1.5 ngN m-2 s-1). Soil moisture was found to be the dominant factor controlling the NO fluxes. Whenever it was not limiting, the diel behaviour of NO emission followed the daily variation of soil temperature measured 1 cm below the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009765510538
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  • 2
    Electronic Resource
    Electronic Resource
    The vertical sulfur dioxide distribution at the tropopause level (1984)
    Springer
    Journal of atmospheric chemistry 2 (1984), S. 175-189 
    Details
    ISSN: 1573-0662
    Keywords: Sulfur dioxide ; stratospheric sulfur budget ; stratospheric-tropospheric exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In 1978–1980 nine aircraft flights to an altitude of up to 15 km were made over western Europe. Sulfur dioxide was measured with a sensitive chemiluminescence method consisting of separate sampling and analysis stages and application of a wet chemical filter procedure (detection limit: 8 pptv SO2). The measurements performed in the upper troposphere and lower stratosphere lead to some unexpected results: (a) the meteorological conditions at the tropopause level have an important influence on the observed SO2 mixing ratio; (b) between the 500 mb and the actual tropopause level the SO2 mixing ratio is found to be 〈100 pptv, and weak vertical gradients of SO2 suggest only a small flux of tropospheric SO2 into the stratosphere; (c) increasing SO2 mixing ratios within the first kilometers of the stratosphere give strong support to a stratospheric source of SO2. In the light of improved one-dimensional models considering the vertical distribution of stratospheric sulfur compounds (Crutzen, 1981; Turco et al. 1981) it can be shown that the oxidation of organic sulfur compounds (e.g., OCS, CS2) seems to be a stratospheric source of SO2. Furthermore, the flux calculations based on the SO2 mixing ratios measured at the tropopause level indicate that the contribution of tropospheric (man-made) SO2 to the stratospheric aerosol layer is of only minor importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00114130
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