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  • 1
    Electronic Resource
    Electronic Resource
    Field study of the emissions of methyl chloride and other halocarbons from biomass burning in Western Africa (1995)
    Springer
    Journal of atmospheric chemistry 22 (1995), S. 67-80 
    Details
    ISSN: 1573-0662
    Keywords: biomass burning ; halocarbons ; hydrocarbons ; methylchloride ; emission ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10−5±0.8×10−5 mol CH3Cl/mol CO2. Based on the global emission rates for CO2 from biomass burning we estimate a range of 226−904×109 g/y as global emission rate with a best estimate of 515×109 g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH2Cl2, CHCl3, CCl4, CH3CCl3, C2HCl3, C2Cl4, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00708182
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    An optimized method for airborne peroxyacetyl nitrate (PAN) measurements (1995)
    Springer
    Journal of atmospheric chemistry 22 (1995), S. 303-317 
    Details
    ISSN: 1573-0662
    Keywords: peroxyacetyl nitrate ; gas-chromatographic optimization ; airborne measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In this paper we describe a gas-chromatographic method for PAN measurements in the background atmosphere, which has been adapted to the special requirements of aircraft based campaigns. The instrument is installed in a 1.21 m high, 19 inch rack which has a total weight of 70 kg and a power consumption of 750 VA. The gas chromatograph is equipped with a commercial liquid injector and a valve system for injection of gaseous samples. The gas-inlet system allows automatic injection of samples with defined and constant mass, independent from ambient pressure variations. Two different methods are used for calibration: Liquid PAN calibration samples and a diffusion source for gas-phase calibrations. Both methods have reproducibilities better than 90% and agree with each other to better than 85%. An optimum selectivity of the gas-chromatographic separation is obtained by a combination of two short megabore capillary columns of different polarity. The flow rates are 15 cm3/min, the column temperature is 26°C. For detection an electron-capture detector, operated at 30°C, is used. To allow a reliable control of these relatively low temperatures the instrument is equipped with peltier cooling. To avoid baseline or signal drifts caused by pressure variations in the aircraft cabin an electronic control of the system pressure is integrated into the instrument. The lower limit of detection is better than 15 ppt (3 σ), the time needed for one measurement is less than 4 min. Preliminary results from a flight campaign conducted in June 1994 demonstrate the suitability of the instrument for airborne PAN measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00696640
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  • 4
    Electronic Resource
    Electronic Resource
    Peroxyacetyl Nitrate (PAN) Measurements During the POPCORN Campaign (1998)
    Springer
    Journal of atmospheric chemistry 31 (1998), S. 139-159 
    Details
    ISSN: 1573-0662
    Keywords: peroxyacetyl nitrate ; rural measurements ; odd oxygen radicals ; photochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract During the POPCORN campaign between 3 and 24 August 1994 we measured peroxyacetyl nitrate (PAN) in a rural area of Mecklenburg-Vorpommern (North-Eastern Germany) above a corn field. A total of about 5000 PAN measurements were carried out within the three weeks of the campaign. Measured PAN mixing ratios ranged from below the detection limit of 10 ppt up to an afternoon maximum of 1 ppb. The mean value of all data was 140 ppt. The daily mean PAN mixing ratios were typically in the range of 50 to 250 ppt, but during a clean air episode PAN mixing ratios of well below 40 ppt were observed. The characteristic relative diurnal variation of the PAN mixing ratios with a late night/early morning minimum and an afternoon maximum persisted during these episodes. The daily averages of the PAN mixing ratios showed clear episodic variations which coincided with the duration of typical synoptic episodes of two to six days duration. Based on the measurements of the various parameters determining the PAN formation and destruction rates, the local budget for PAN was calculated. During daytime the calculated net photochemical formation rate of PAN was nearly always significantly higher than the observed change of the PAN concentration. This demonstrates that substantial amounts of PAN (often in the range of several hundred ppt/h) were exported from the corn field. The resulting removal of NOx to some extent effects the budget of nitrogen oxides (NOx), but the export of odd oxygen radicals in the form of PAN during daytime often amounted up to 30–50% of the OH-radical formation by ozone photolysis. Thus the importance of PAN as reservoir and transport medium for odd oxygen radicals can be very substantial and may have a significant impact on the budget and distribution of odd oxygen radicals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006004031055
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