Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    Emission of nitrous oxide from temperate forest soils into the atmosphere
    ( 1988)
    Schmidt, J.
    ;
    Conrad, R.
    ;
    Seiler, W.
    N2O emission rates were measured during a 13-month period from July 1981 till August 1982 with a frequency of once every two weeks at six different forest sites in the vicinity of Mainz, Germany. The sites were selected on the basis of soil types typical for many of the Central European forest ecosystems. The individual N2O emission rates showed a high degree of temporal and spatial variabilities which, however, were not significantly correlated to variabilities in soil moisture content or soil temperatures. However, the N2O emission rates followed a general seasonal trend with relatively high values during spring and fall. These maxima coincided with relatively high soil moisture contents, but may also have been influenced by the leaf fall in autumn. In addition, there was a brief episode of relatively high N2O emission rates immediately after thawing of the winter snow. The individual N2O emission rates measured during the whole season ranged between 1 and 92 myg N2O-N m E-2 h E-1. T he average values were in the range of 3-11 myg N2O-N m E-2 h E-1 and those with a 50% probability were in the range of 2-8 myg N2O-N m E-2 h E-1. The total source strength of temperate forest soils for atmospheric N2O may be in the range of 0.7-1.5 Tg N yr E-1. (IFU)
  • Publication
    Influence of surface microlayer on the flux on nonconservative trace gases -CO, H2, CH4, N2O- across the ocean-atmosphere interface
    ( 1988)
    Conrad, R.
    ;
    Seiler, W.
    Gas exchange experiments were conducted in the tropical Atlantic Ocean during a ship expedition with FS Meteor using a small rubber raft. The temporal change of the mixing ratios of CO, H2, CH4 and N2O in the headspace of a floating glass box and the concentrations of these gases in the water phase were measured to determine their transfer velocities across the ocean-atmosphere interface. The ocean acted as a sink for these gases when the water was undersaturated with respect to the mixing ratio in the headspace. The transfer velocities were different for the individual gases and showed still large differences even when normalized for diffusivity. Applying the laminar film model, film thicknesses of 20 to 70 mym were calculated for the observed flux rates of the different gas species. When the water was supersaturated with respect to atmospheric CO, H2, CH4 and N2O, the transfer velocities of the emission process were smaller than those determined for the deposition process. In case of H2 and CH4, emission was even not calculable although, based on the observed gradient, the laminar film model predicted significant fluxes at the air-sea interface. The results are interpreted by destruction processes active within the surface microlayer. (IFU)
  • Publication
    Tropospheric chemical composition measurements in Brazil during the dry season
    ( 1985)
    Crutzen, P.J.
    ;
    Delany, A.C.
    ;
    Greenberg, J.
    ;
    Haagenson, P.
    ;
    Heidt, L.
    ;
    Lueb, R.
    ;
    Pollock, W.
    ;
    Seiler, W.
    ;
    Wartburg, A.
    ;
    Zimmermann, P.
    Field measurement programs in Brazil during the dry seasons in August and September 1979 and 1980 have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NOx, N2O, CH4 and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NOx by lightning, there is probably a large production of O3 in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer. (IFU)
  • Publication
    Distribution, speciation, and budget of atmospheric mercury
    ( 1985)
    Slemr, F.
    ;
    Schuster, G.
    ;
    Seiler, W.
    Total gaseous mercury (TGM) concentrations over the Atlantic Ocean and over Central Europe were measured repeatedly in the years 1978-1981. The latitudinal TGM distribution showed a pronounced and reproducible interhemispherical difference with higher TGM concentrations in the Northern Hemisphere. TGM was found to be vertically well mixed within the troposphere. The TGM concentrations seems to increase with time at a rate of 10 +- 8%/yr in the Northern and 8 +- 3%/yr in the Southern Hemisphere. Measurements of mercury speciation showed that elemental mercury is the main TGM component contributing more than 92% and 83% of TGM in marine and continental air, respectively. The tropospheric mercury burden was calculated to be 6 x 10 E9g. The interhemispheric distribution and temporal and spatial variability of TGM imply a tropospheric residence time of TGM of about 1 yr. Sink strengths calculated independently from the measured mercury concentration on particles and in rainwater are consist ent with the above figures. (IFU)
  • Publication
    Methane emission from rice paddies
    ( 1984)
    Seiler, W.
    ;
    Conrad, R.
    ;
    Holzapfel-Pschorn, A.
    ;
    Scharffe, D.
    Methane release rates from rice paddies have been measured in Andalusia, Spain, during almost a complete vegetation period in 1982 using the static box system. The release rates ranged between 2 and 14 mg/square meter/h and exhibited a strong seasonal variation with low values during the tillering stage and shortly before harvest, while maximum values were observed at the end of the flowering stage. The CH4 release rate, averaged over the complete vegetation period, accounted for 4 mg/square meter/h which results in a worldwide CH4 emission from rice paddies of 35-59 x 10 E12 g/yr if we assume that the observed CH4 release rates are representative of global conditions. The CH4 release rates showed diurnal variations with higher values late in the afternoon which were most likely caused by temperature variations within the upper layers of the paddy soils. Approximately 95% of the CH4 emitted into the atmosphere by rice paddies was due to transport through the rice plants. Transport by b ubbles or diffusion through the paddy water was of minor importance. Incubation experiments showed that CH4 was neither produced nor consumed in the paddy water. The release of CH4 from rice paddies caused a diurnal variation of CH4 in ambient air within the rice-growing area with maximum values of up to 2.3 ppmv during the early morning, compared to average daytime values of 1.75 ppmv. (IFU)
  • Publication
    The latitudinal distribution of carbon monoxide across the Pacific from California to Antarctica
    ( 1984)
    Seiler, W.
    ;
    Robinson, E.
    ;
    Clark, D.
    The results of a research study of the carbon monoxide concentration from California to 90 degrees S, Antarctica are presented. The data both extend and support other research studies of the latitudinal distribution of carbon monoxide in that higher concentrations are evident over the Northern Hemisphere than over the Southern Hemisphere. Carbon monoxide concentrations range between 50 to 60 ppb with a few peaks into the 60s in the latitudinal area south of the ITCZ and values of 80 ppb or higher at latitudes north of Hawaii. A comparison is also made of carbon monoxide and ozone concentrations along the flight tract between California and Antarctica, over the Ellsworth Mountains of Antarctica, and between 78 degrees S and the South Pole. These ozone-carbon monoxide data show statistically significant negative correlations in the upper troposphere and lower stratosphere over Antarctica. It is believed that this is a good indication of mixing across the tropopause. (IFU)
  • Publication
    Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils
    ( 1984)
    Seiler, W.
    ;
    Conrad, R.
    ;
    Scharffe, D.
    The flux of CH4 and CO2 from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH4 relative to the flux rate of CO2 in terms of carbon obtained for the individual species showed ratios of 2.9 x 10 E-3, 7.0 x 10 E-4, 6.7 x 10 E-5; 8.7 x 10 E-3, 2.0 x 10 E-3 and 4.2 x 10 E-3, respectively. Using data published on the assimilation efficiencies of termites, the flux of carbon as CH4 accounts for 6.0 x 10 E-5 to 2.6 x 10 E-3 of the carbon ingested which results in a global CH4 emission by termites of 2 to 5 x 10 E12 g/yr. Methane is decomposed in the soil with average decomposition rates of 52 myg/square meter/h. The annual CH4 consumption in the tropics and subtropics is estimated to be 21 x 10 E12 g which exceeds the CH4 emission rate by termites. (IFU)
  • Publication
    Nitrous oxide emissions from fertilized and unfertilized soils in a subtropical region -Andalusia, Spain-
    ( 1984)
    Seiler, W.
    ;
    Conrad, R.
    ;
    Slemr, F.
    Field measurements of N2O emission rates were carried out from August until October 1982 in a subtropical region in Europe, i.e. in Andalusia, Spain. The measurements were performed by using an automatic sampling and analysis technique allowing the semi-continuous determination of N2O emission rates. The N2O emission rates were positively correlated to the soil surface temperature and exhibited a diurnal rhythm with maximum rates in the afternoon and minimum rates in the early morning with average values of 1 myg N2O-N/square meter/h for the grass lawn and 15 myg N2O-N/square meter/h for cultivated land. Application of urea and ammonium nitrate resulted in elevated N2O emission rates when compared to the unfertilized control. The loss of fertilizer-nitrogen as N2O was 0.18% for urea and 0.04% for NH4NO3 which compares very well with data obtained in a temperate climate (Germany). The total source strength of fertilizer-derived N2O is estimated to be 0.01-2.2 Tg N2O-N per year. The N2O flux from unfertilized natural soils may be as high as 4.5 Tg N2O-N, indicating that the N2O emission from soils contributes significantly to the global N2O budget. (IFU)