Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    In situ CO concentrations at the sites Zugspitze (47 deg N, 11 deg E) and Cape Point (34 deg S, 18 deg E) in April and October 1994
    ( 1998)
    Scheel, H.E.
    ;
    Brunke, E.-G.
    ;
    Sladkovic, R.
    ;
    Seiler, W.
    Continuous measurements of CO have been performed at the coastal site Cape Point (34 deg S, 18 deg E) and at the continental mountain site Zugspitze (47 deg N, 11 deg E) since 1978 and 1990, respectively. The CO concentrations observed at both stations in 1994 during the periods April 9 - 18, and September 30 to October 10 were studied in detail with the aim to supplement CO observations from space made by NASA during two shuttle flights (measurement of air pollution from satellites (MAPS) project). All CO values reported were adjusted to the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) calibration scale. CO mixing ratios at Cape Point comprised episodes of baseline CO levels in maritime air (average: 48.8 ppb (April); 69.4 ppb (September/October)) and of elevated levels related to continental air and regional pollution (average: 89.5 ppb (April); 102.1 ppb (September/October)). During the same periods the mean CO mixing ratio at the Zugspitze amounted to 220.1 ppb (range 150 - 358 ppb) and 124.8 ppb (range 78 - 175 ppb), respectively. Due to the prevailing airflow, CO levels at the Zugspitze were unusually high compared to the longterm average during the April mission (time of seasonal maximum). In contrast, they were close to the average during the October mission. Baseline concentrations at Cape Point were about 3 - 4 ppb above the long-term average for both April (increasing side of seasonal cycle) and October (time of seasonal maximum), which is within the range of normal interannual variability. A preliminary comparison with the MAPS data for the respective geographic regions showed good agreement of the CO mixing ratios for clean air at Cape Point in April and at the Zugspitze in October. In addition, the CO levels observed in continental air at Cape Point in October agreed well with the MAPS data. Obvious differences in CO concentrations for other parts of the records mainly reflected uncomparable atmospheric conditions. In particular, they seem ed to be related to either vertical gradients of CO or small-scale differences in air mass composition as indicated by meteorological analyses.
  • Publication
    A SVAT scheme for NO, NO2, and O3. Model description and test results
    ( 1996)
    Kramm, G.
    ;
    Beier, N.
    ;
    Foken, T.
    ;
    Müller, H.
    ;
    Schröder, P.
    ;
    Seiler, W.
    A soil/vegetation/atmosphere transfer (SVAT) scheme for determining the dry deposition and/or emission fluxes of NO, NO2, and 03, in the atmospheric surface layer over horizontally uniform terrain covered with fibrous canopy elements is presented and discussed. This transfer scheme is based on the micrometeorological ideas of the transfer of momentum, heat and matter near the Earth's surface, where chemical reactions between these trace gases are included. The fluxes are parameterized by first-order closure principles. The uptake processes by vegetation and soil are described in accord with Deardorff (1978). The SVAT scheme requires only routine data of wind speed, dry- and wet-bulb temperatures, short wave and long wave radiation, and the concentrations of 0, and nitrogen species provided by stations of monitoring networks. First model results indicate that the dry deposition fluxes of NO, NO2, and O3 are not only influenced by meteorological and plant-physiological parameters, but also by chemical reactions between these trace species and by NO emission from the soil. Furthermore, a small displacement in the concentrations of NO, NO2, and O3 within in the range of the detection limits of the chemical sensors can produce large discrepancies in the flux estimates, which are manifested here by the shift from height-invariant fluxes substantiated by the photostationary state to strongly height-dependent fluxes caused by the departure from that state. Especially in the case of these nitrogen species the widely used 'big leaf' multiple resistance approach, which is based on the constant flux approximation seems to be inappropriate for computing dry deposition fluxes and deposition velocities.
  • Publication
    Temporal patterns of methane emissions from wetland rice fields treated by different modes of N application
    ( 1994)
    Wassmann, R.
    ;
    Neue, H.U.
    ;
    Lantin, R.S.
    ;
    Aduna, J.B.
    ;
    Alberto, M.C.R.
    ;
    Andales, M.J.
    ;
    Tan, M.J.
    ;
    Denier Van der Gon, H.A.C.
    ;
    Hoffmann, H.
    ;
    Papen, H.
    ;
    Rennenberg, H.
    ;
    Seiler, W.
    Methane emission rates from wetland rice fields were determined in Los Banos (Philippines) using an automatic system that allows continuous measurements over time. Methane emission was monitored in an irrigated Aquandic Epiaqualf planted to rice cultivar IR72. Urea fertilizer was applied using four modes: (1) broadcast 10 days after transplanting, (2) broadcast at transplanting, (3) broadcast and incorporated at final harrowing, and (4) deep placement as sulfur-coated granules. The treatments were laid out in a randomized complete block design with four replicates. Measurements were done in the 1991 wet season, 1992 dry season (four treatments), and the 1992 wet season (only treatment 3). Methane emission rates from the experimental plots showed pronounced seasonal and diel variations. The diel pattern of methane emission rates followed a consistent pattern, with highest rates observed in the early afternoon and lowest rates in the early morning. Methane emission rate was generally hig hest at the ripening stage. The average methane emission rate during the 1992 dry season (190 mg CH4 m(-2) d(-1)) exceeded the average flux rates of the 1992 wet season (79 mg CH4 m(-2) d(- 1)) by a factor of 2.4. The total methane emitted from these flooded rice fields amounted to 19 g CH4 m(-2) in the dry season with rice yields of 5.2-6.3 t ha(-1) and 7 g CH4 m(-2) in the wet season with rice yields of 2.4-3.3 t ha(-1) regardless of the mode of N application. Significant amounts corresponding to 20 per cent of the methane released under waterlogged conditions were released when the soil was drained after harvest. Emission rates increased sharply when the floodwater receded and macropores started to drain. Emission of methane stopped only when the soil became fully aerated.
  • Publication
  • Publication
    A 3-year continuous record on the influence of daytime, season, and fertilizer treatment on methane emission rates from an Italian rice paddy.
    ( 1989)
    Holzapfel-Pschorn, A.
    ;
    Conrad, R.
    ;
    Rennenberg, H.
    ;
    Schütz, H.
    ;
    Seiler, W.
    CH4 emission rates have been measured in an Italian rice paddy between 1984 and 1986, covering three vegetation periods. For these measurements a fully automated, computerized sampling and analyzing system was developed which allowed the simultaneous determination of CH4 emission rates at 16 different field plots. CH4 emission rates showed strong diurnal and seasonal variations. Diurnal changes correlated with changes in soil temperature. During the season, CH4 emission rates showed a first maximum in May-June before tillering and a second maximum in July during the reproductive stage of the rice plants. In 1985 and 1986 two maxima were observed during summer in addition to the first maximum in the rate of CH4 emission during spring. Application of mineral and/or organic fertilizer strongly influenced the CH4 emission rates, depending on the type, rate, and mode of fertilizer application. Thus the rates decreased by at most 40% and 60% after fertilization by deep incorporation with 200 kg N/ha urea and 200 kg N/ha ammonium sulfate, respectively. Application of 200 kg N/ha calcium cyanamide led to a reduction of the first maximum of CH4 emission but caused the second maximum to increase, the overall result being that the seasonally averaged CH4 emission rate was comparable to that observed in unfertilized fields.
  • Publication
    Methane production by domestic animals, wild ruminants, other herbivorous fauna, and humans
    ( 1986)
    Crutzen, P.J.
    ;
    Aselmann, I.
    ;
    Seiler, W.
    A detailed assessment of global methane production through enteric fermentation by domestic animals and humans is presented. Measured relations between feed intake and methane yields for animal species are combined with population statistics to deduce a current yearly input of methane to the atmosphere of 74 Tg (1 Tg = 10 E12 g), with an uncertainty of about 15%. Of this, cattle contribute about 74%. Buffalos and sheep each account for 8-9%, and the remainder stems from camels, mules and asses, pigs, and horses. Human CH4 production is probably less than 1 Tg per year. The mean annual increase in CH4 emission from domestic animals and humans over the past 20 years has been 0.6 Tg, or 0.75% per year. Population figures on wild ruminants are so uncertain that calculated CH4 emissions from this source may range between 2 Tg and 6 Tg per year. Current CH4 emission by domestic and wild animals is estimated to be about 78 Tg, representing 15-25% of the total CH4 released to the atmosphere fr om all sources. The likely CH4 production from domestic animals in 1890 was about 17 Tg, so that this source has increased by a factor of 4.4. A brief tentative discussion is also given on the potential CH4 production by other herbivorous fauna, especially insects. Their total CH4 production probably does not exceed 30 Tg annually. (IFU)
  • Publication
    Methane emission during a cultivation period from an Italian rice paddy
    ( 1986)
    Holzapfel-Pschorn, A.
    ;
    Seiler, W.
    CH4 release rates from rice paddies were measured in Vercelli, Italy, in 1983 during a complete vegetation period, using a static box system. The rice paddies were found to be a source of atmospheric methane during the time of flooding. The CH4 release rates range between a few milligrams of CH4 per square meter per hour and 51 mg CH4 m E-2 h E-1 and show a seasonal variation with maximum emission rates between tillering and flowering. Averaged over the complete vegetation period, the CH4 release rate accounts for 16 mg m E-2 h E-1. The CH4 release rates show strong diurnal variations, with highest values in the late afternoon and lowest values in the early morning, which coincides with the temperature variation in the upper soil layer (1-10 cm). CH4 is almost exclusively emitted into the atmosphere by gas bubbles during the first 6 weeks after flooding the rice paddies, that is, on fields without vegetation. Afterwards, 80% of the observed CH4 transport from the paddy soil into the at mosphere was due to diffusion through the stems of the rice plants. Transport by diffusion through the paddy water appeared to be of minor importance. The global annual CH4 emission from rice paddies is estimated to be of the order of 39-94 Tg yr E-1 (Tg=10 E12 g) for 1940 conditions and 70-170 Tg yr E-1 for 1979 conditions, indicating a secular trend of the CH4 emission by rice paddies of about 1,6% per year during the last 35 years. (IFU)
  • Publication
    Influence of temperature, moisture, and organic on the flux of H2 and CO between soil and atmosphere - field studies in subtropical regions
    ( 1985)
    Conrad, R.
    ;
    Seiler, W.
    Production and deposition rates of atmospheric hydrogen and carbon monoxide were studied during field measurements in subtropical regions, i.e., Transvaal (South Africa), Andalusia (Spain), and the Karoo (South Africa). Measurements were carried out by applying static and equilibrium box techniques. The equilibrium technique has been introduced as a novel method to measure production and destruction rates simultaneously even when soil conditions (e.g., temperature) change during the course of the measurements. Deposition velocities of H2 and CO were virtually independent of the soil temperature measured in 3- to 10-mm depths and agreed with those measured in the temperate regions. H2 production by soil was not observed. By contrast, CO was produced by soil in a dark chemical reaction. Production rates increased exponentially with soil temperatures, giving activation energies of 57-110 kJ mol E-1 and increased linearly with soil organic carbon content. CO production rates followed a die l rhythm parallel to soil surface temperatures. Production generally exceeded CO deposition during the hot hours of the day, so that arid subtropical soils act as a net source of atmospheric CO during this time. On a global basis, CO production by soil may reach source strengths of 30 Tg yr E-1, which is considerably less than the global deposition of CO estimated to be 190-580 Tg yr E-1. Global H2 deposition rates were estimated to 70-110 Tg yr E-1. (IFU)
  • Publication
    Contribution of CH4 produced in rice paddies to the global CH4 budget
    ( 1984)
    Holzapfel-Pschorn, A.
    ;
    Seiler, W.
    CH4 release rates from rice paddies have been measured at several paddy fields in Spain, USA and Italy. The results show strong seasonal variations of the CH4 release rates with maximum values at the end of the flowering stage. The CH4 release rates averaged over the total vegetation period range between 4 and 17 mg CH4/qm h resulting in a worldwide CH4 emission by rice paddies of 33-83x10 E12 g/yr or 10-20% of the global atmospheric CH4 budget in 1979. Because of the smaller harvest area of rice paddies, the CH4 emission in 1950 accounts for about 20-51x10 E12 g/yr indicating an increase of the CH4 emission rates by rice paddies of about 1-2% per year. The CH4 release rates from rice paddies show daily variations with maximum values in the afternoon correlating with the soil temperatures. Most of the CH4 produced in the rice paddy soil is emitted into the atmosphere due to diffusion through the rice plant. Transport by bubbles seems to be of minor importance. (IFU)