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  • 1
    Electronic Resource
    Electronic Resource
    TROPOZ II: Global distributions and budgets of methane and light hydrocarbons (1996)
    Springer
    Journal of atmospheric chemistry 25 (1996), S. 115-148 
    Details
    ISSN: 1573-0662
    Keywords: NMHC budget ; tropospheric distributions ; methane budget ; TROPOZ II experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract One hundred atmospheric samples were collected aboard the French Caravelle research aircraft, during the TROPOZ II experiment (January 1991). Tropospheric meridional distributions versus height were then derived from 70° N to 60° S and between 0.25 km and 11 km for methane, acetylene, ethane and propane. Areas of significant emissions were identified over northern latitudes with, for acetylene, maximum mixing ratios in the north (1.896 ppbv) more than 70 times higher than in background southern latitudes (0.025 ppbv). The influence of emissions from biomass burning was also obvious in the tropical boundary layer. Significant dynamic phenomena led to high mixing ratio zones above 8 or 10 km even for the most reactive hydrocarbons. For the first time, simultaneous assessment of global tropospheric contents of several light hydrocarbons was carried out. Using TROPOZ II data (January 1991) and STRATOZ III data (June 1984) collected by Rudolph (1988) during similar aircraft flights in 1988, the following tropospheric loads (in Tg-compound) were estimated, in January 1991 and June 1984, respectively: 1.1 and 0.4 for acetylene, 5.0 and 3.9 for ethane, 3.6 and 1.4 for propane and 3545 for methane in January only. According to our results, 40 to 65% of acetylene and alkanes are oxidized in the tropics. In addition, by computing the annual tropospheric sink of acetylene and alkanes, an evaluation of their annual global fluxes was performed. The figures are, in Tg-compound y-1 with an uncertainty of 80% to an order of magnitude, based on January and June data, respectively: 10 and 6.6 for acetylene, 16.3 and 17.6 for ethane and 52.3 and 26.5 for propane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00053788
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  • 2
    Electronic Resource
    Electronic Resource
    Field study of dimethylsulfide oxibation in the boundary layer: Variations of dimethylsulfide, methanesulfonic acid, sulfur dioxide, non-sea-salt sulfate and aitken nuclei at a coastal site (1992)
    Springer
    Journal of atmospheric chemistry 14 (1992), S. 459-477 
    Details
    ISSN: 1573-0662
    Keywords: Dimethylsulfide ; Methanesulfonie acid ; Sulfur dioxide ; Non-sea-salt sulfate ; Aitken Nuclei ; Coastal area ; Dimethylsulfide Oxidation Mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Measurements of atmospheric dimethylsulfide (DMS) and its oxidation products, sulfur dioxide (SO2), methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4 2-) were monitored during the period June 9–26, 1989 at a coastal site in Brittany. As indicated by the radon (Rn-222) activities and the high concentrations of NOx the air masses, for most of the experiment, were continental in origin. The observed concentrations range from 1.9 to 65 nmol/m3 for DMS (n=157), 0.6 to 94.2 nmol/m3 for SO2 (n=50), 0.6 to 11.6 nmol/m3 for MSA (n=44) and 42 to 350 nmol/m3 for nss-SO4 2- (n=44). Aitken nuclei reached values as high as 4.5 × 105 particles/m3. When continental conditions predominated, the measured SO2 concentrations were lower than those expected from a consideration of the observed DMS concentrations and the existence of SO2 background of the continental air masses. Similarly, compared to the MSA/DMS ratio in the marine atmosphere, higher concentrations of MSA were observed than those expected from the measured levels of DMS. The presence of enhanced levels of MSA was also endorsed by the observation that the measured mean MSA/nss-SO4 2- ratio of 6±3% was similar to the mean value of 6.9% observed in the marine atmosphere. These above observations are in line with recent laboratory findings by Barnes et al. (1988), which show an increase of the MSA/DMS yield with a simultaneous decrease of the SO2/DMS yield in the presence of NOx.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115251
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  • 3
    Electronic Resource
    Electronic Resource
    Methane, carbon monoxide and light non-methane hydrocarbon emissions from African savanna burnings during the FOS/DECAFE experiment (1995)
    Springer
    Journal of atmospheric chemistry 22 (1995), S. 149-162 
    Details
    ISSN: 1573-0662
    Keywords: biomass burning ; hydrocarbons ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Atmospheric samples from savanna burnings were collected in the Ivory Coast during two campaigns in January 1989 and January 1991. About 30 nonmethane hydrocarbons from C2 to C6, carbon monoxide, carbon dioxide and methane were measured from the background and also at various distances from the burning. Concentrations in the fire plume reached ppmv levels for C2-C4 hydrocarbons, and 5300, 500 and 93 ppmv for CO2, CO and CH4 respectively. The excess in the mixing ratios of these gases above their background level is used to derive emission factors relative to CO and CO2. For the samples collected immediately in the fire plume, a differentiation between high and low combustion efficiency conditions is made by considering the CO/CO2 ratio. Ethene (C2H4), acetylene (C2H2), ethane (C2H6) and propene (C3H6) are the major NMHC produced in the flaming stage, whereas a different pattern with an increasing contribution of alkanes is observed in samples typical of post flaming processes. A strong correlation between methane and carbon monoxide suggests that these compounds are produced during the same stage of the combustion. In samples collected at a distance from the fire and integrated over a period of 30 minutes, the composition is very similar to that of flaming. ΔNMHC/ΔCO2 is of the order of 0.7%, ΔCH4/ΔCO2 of the order of 0.4% and ΔCO/ΔCO2 of the order of 6.3%. From this study, a global production by African savanna fires is derived: 65 Tg of CO-C, 4.2 Tg of CH4-C and 6.7 Tg of NMHC-C. Whereas acetylene can be used as a conservative tracer of the fire plumes, only ethene, propene and butenes can be considered in terms of their direct photochemical impact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708186
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  • 4
    Electronic Resource
    Electronic Resource
    Calcitonin gene-related peptide and islet amyloid polypeptide stimulate insulin secretion in RINm5F cells through a common receptor coupled to a generation of cAMP (1994)
    Springer
    Bioscience reports 14 (1994), S. 1-13 
    Details
    ISSN: 1573-4935
    Keywords: CGRP receptor ; cAMP, insulin release ; IAPP ; pancreatic β cell: RINm5F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The question as to whether the homologous peptides CGRP and IAPP can regulate insulin secretion in RINm5F cells was addressed. Chicken CGRP displayed a reproducible inhibitory effect on insulin secretion within 0.1 and 1 nM concentrations and a stimulatory effect at higher concentrations. The maximal stimulatory effects on insulin secretion were obtained with 1.0 μM of chicken CGRP (cCGRP), human α-CGRP (h α-CGRP) and human IAPP (hIAPP) which caused 246 ± 22, 302 ± 63 and 224 ± 14 percent increases of control levels, respectively (p 〈 0.001). Similarly, maximal accumulations of cAMP were obtained with 1.0 μM of cCGRP, h α-CGRP and hIAPP with the respective percent increases of control levels of 587 ± 24, 436 ± 41 and 410 ± 25 (p 〈 0.005). Thus the stimulatory effects on insulin secretion in RINm5F cells by cCGRP, h α-CGRP and hIAPP appear to be mediated by the cAMP pathway. Chicken CGRP, the most potent peptide tested, displayed a correlated dose response stimulation of intracellular cAMP and insulin release within the concentration range of 10–1000nM. The EC50 values of cCGRP for cAMP accumulation and insulin release were similar (20nM and 10 nM respectively). The stimulatory effect of IAPP on cAMP was not additive with that of cCGRP suggesting that IAPP action was mediated by CGRP receptors. This hypothesis was further sustained by a preferential inhibition of125I[His]h α-CGRP binding to RINm5F cells by cCGRP as compared to IAPP. We conclude that CGRP and IAPP, through a direct action on a chicken CGRP preferring receptor present in β cells, stimulated insulin by a cAMP mediated pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01901633
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