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  • 1
    Electronic Resource
    Electronic Resource
    Emission of nitric oxide from soils and termite nests in a Trachypogon savanna of the Orinoco basin (1993)
    Springer
    Journal of atmospheric chemistry 17 (1993), S. 293-306 
    Details
    ISSN: 1573-0662
    Keywords: NO soil fluxes ; tropical savanna ; termites ; vegetation burning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nitric oxide fluxes from soils in the Trachypogon savanna of the Orinoco basin were determined during the dry season using the static chamber method. The emission from dry soils fluctuated from 0.4 to 3 ng N m−2 s−1 and increased up to 25 ng N m−2 s−1 after moderate watering or light rain-falls (1 to 5 mm). The mean emission values are up to 6 times lower than one observed earlier at the Chaguaramas site, but up to 10 times higher than one recorded at the Guri site, indicating an important spatial variability in NO fluxes of the Venezuelan savanna region. The changes observed after the addition of nitrogen to the soil, in the form of ammonium and/or nitrate, indicate a high denitrification potential in this acidic soil. Burning of the surface vegetation produced an increase by a factor of 10 in the emission rate of NO, but the effect was relatively short in time, about 5 days. It was estimated for the savanna region that burning increases the total NO soil emission during the dry season by 15% compared to the unburnt case. Soils with termite nests emit 10 times more NO than soil without nests, but the contribution from this source is less than 2% of the total savanna soil flux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00694402
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  • 2
    Electronic Resource
    Electronic Resource
    Natural and anthropogenic C2 to C6 hydrocarbons in the central-eastern Venezuelan atmosphere during the rainy season (1996)
    Springer
    Journal of atmospheric chemistry 25 (1996), S. 201-214 
    Details
    ISSN: 1573-0662
    Keywords: nonmethane hydrocarbons ; isoprene ; tropical atmosphere ; oil field emissions ; potential ozone formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The levels of low molecular weight hydrocarbons were measured at pristine sites and rural locations affected by hydrocarbon emissions from oil and gas producing fields in Venezuela. At the clean sites, lower concentrations of C2 to C6 alkanes were observed, whereas, in comparison with remotes sites, very much higher levels were measured at the polluted sites. Alkenes present relatively high concentrations, with isoprene being the most abundant, all over the study region. The main sources of alkenes are likely to be natural, mainly from vegetation. The levels of alkanes recorded at the clean sites and the alkene levels found everywhere in the region are in agreement with the values reported for other clean sites in the tropics. The increase of ozone production capacity due to the anthropogenic emissions of alkanes from oil and gas fields was estimated. Due to the presence in the atmosphere of important amounts of naturally emitted isoprene, ethene and propene, which makes a substantial contribution to the reactivity of the hydrocarbon mixture, a small increase (〈5%) was estimated to occur in the capacity of the ozone production at a regional scale during the rainy season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00053791
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Seasonal variation of gaseous HNO3 and NH3 at a Tropical Savannah site (1990)
    Springer
    Journal of atmospheric chemistry 11 (1990), S. 245-254 
    Details
    ISSN: 1573-0662
    Keywords: Nitric acid ; ammonia ; tropical atmosphere ; vegetation burning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Gaseous nitric acid and ammonia were sampled with annular denuders at a forest savannah site from April to December 1987. The analysis of the extract was made spectrophotometrically and by a selective electrode for NO3 − and NH4 +, respectively. Higher concentrations were observed during the vegetation burning period at the end of the dry season. In the studied savannah area, large soil emissions of NO occur during the rainy season, although very low concentrations of HNO3 (0.035 ppb) and also of particulate NO3 − (0.43 μg m-3) were observed; it is likely that NOx are lost by fast vertical transport to the upper troposphere. During the nonburning period, the average concentration of NH3 was 2.7 ppb, which is much lower than values given in the literature for the tropical America atmosphere. The concentrations of HNO3 and NH3 were always below the values needed to produce ammonium nitrate aerosols.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00118351
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Particle-size distribution of inorganic water soluble ions in the venezuelan savannah atmosphere during burning and nonburning periods (1988)
    Springer
    Journal of atmospheric chemistry 7 (1988), S. 369-388 
    Details
    ISSN: 1573-0662
    Keywords: Savannah atmosphere ; vegetation burning ; soluble particles ; particles size distributions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The results presented are the first complete analysis of inorganic soluble ions in a tropical savannah region. Atmospheric particles were collected in six rural Venezuelan savannah sites. Concentrations and size distribution of NO3 −, SO4 2-, CI−, PO4 3-, NH4 +, Na+, K+, Ca2+ and Mg2+ were determined in samples collected with Hi Vol samplers equipped with five-stage cascade impactors. Concentrations were higher in the dry season, with a maximum during the burning periods. Using Na+ as a reference, the results show a deficit of Cl− and, with the exception of Mg2+, an enrichment of all other ions with respect to marine aerosols. Significant variations were observed in particle-size distribution between different periods. Various pairs of ions present similar size distributions: SO4 2- and NH4 +; Cl− and Na+; PO4 3- and K+; Ca2+, Mg2+ and NO3 −; indicating that the ions were produced by the same source and/or were involved in similar atmospheric processes. Possible primary sources, the gas-to-particle atmospheric process, environmental implication of long-range transport of nutrients during dry seasons, etc., are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00058711
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    Paper (German National Licenses)
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