Now showing 1 - 10 of 72
  • 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
    Ground-based measurements of ozone and related precursors at 47 deg N 11 deg E
    ( 1997)
    Scheel, H.E.
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    Sladkovic, R.
    ;
    Seiler, W.
  • Publication
    Ozone formation, destruction and exposure in Europe and the United States
    ( 1997)
    Stockwell, W.R.
    ;
    Kramm, G.
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    Scheel, H.E.
    ;
    Mohnen, V.A.
    ;
    Seiler, W.
  • Publication
    Spatial and seasonal distribution of organic amendments affecting methane emission from Chinese rice fields
    ( 1996)
    Wassmann, R.
    ;
    Shangguan, X.J.
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    Tölg, M.
    ;
    Cheng, D.X.
    ;
    Wang, M.X.
    ;
    Papen, H.
    ;
    Rennenberg, H.
    ;
    Seiler, W.
    The effect of fertilizers on methane emission rates was investigated using an automated closed chamber system in Chinese rice fields (Hunan Province). Each of three experiments compared two fields treated with a first uniform fertilizer dose and a second fertilizer dose which was different for each of the two fields. The uniform fertilizer doses for both fields in each experiment comprised mineral (experiment 1), organic (experiment 2) and combined mineral plus organic components (experiment 3). In all three experiments the second fertilizer dose comprised organic amendments for field 1 and no organic amendments for field 2. The rate of increase in methane emission with a given amount of organic manure was found to depend on the total amount of organic manure applied. A single dose of organic manure increased the emission rates by factors of 2.7 to 4.1 as compared to fields without organic manure (experiment 1). In rice fields that had already been treated with organic manure, the appl ication of a second dose of organic manure only slightly enhanced the emission rates in experiment 2 by factors of 1.1 to 1.5 and showed no detectable increase in experiment 3. The net reduction achieved by separation of organic and mineral fertilizers was maximized by concentrating the organic amendments in the season with low emission rates, i.e. early rice, and using exclusively mineral fertilizers on late rice when emission rates were generally higher. This distribution pattern, which was not associated with significant yield losses, resulted in an annual methane emission corresponding to only 56 per cent of the methane emitted from fields treated with blended fertilizers.
  • 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
    Fluxes and pools of methane in wetland rice soils with varying organic inputs
    ( 1996)
    Wassmann, R.
    ;
    Neue, H.U.
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    Alberto, M.C.R.
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    Lantin, R.S.
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    Bueno, C.
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    Llenaresas, D.
    ;
    Arah, J.R.M.
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    Papen, H.
    ;
    Seiler, W.
    ;
    Rennenberg, H.
    Measurements of methane emission rates and concentrations in the soil were made during four growing seasons at the International Rice Research Institute in the Philippines, on plots receiving different levels of organic input. Fluxes were measured using the automated closed chambers system (total emission) and small chambers installed between plants (water surface flux). Concentrations of methane in the soil were measured by collecting soil cores including the gas phase (soil-entrapped methane) and by sampling soil solution in situ (dissolved methane). There was much variability between seasons, but total fluxes from plots receiving high organic inputs (16-24 g CH4 m(- 2)) always exceeded those from the low input plots (3-9 g CH4 m(-2) ). The fraction of the total emission emerging from the surface water (presumably dominated by ebullition) was greater during the first part of the season, and greater from the high organic input plots (35-62 per cent) than from the low input plots (15-2 3 per cent). Concentrations of dissolved and entrapped methane in the low organic input plots increased gradually throughout the season; in the high input plots there was an early-season peak which was also seen in emissions. On both treatments, periods of high methane concentrations in the soil coincided with high rates of water surface flux whereas low concentrations of methane were generally associated with low flux rates.
  • Publication
    Modeled vertical profiles of fluxes and concentrations of atmospheric trace constituents and their modification by chemical reactions
    ( 1995)
    Kramm, G.
    ;
    Müller, H.
    ;
    Schröder, P.
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    Seiler, W.
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    Dlugi, R.
    ;
    Seiler, T.
    ;
    Foken, T.
    ;
    Mölders, N.
    ;
    Sievering, H.
    Dry deposition of ozone and reactive nitrogen compounds, such as NO, NO2, HNO3, NH3, and NH4NO3, is examined in the context of numerical methods. These methods are based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat, and matter near the Earth's surface, where chemical reactions among these trace species are taken into consideration. The fluxes in the turbulent region of the atmospheric surface layer are parameterized by first-order closure principles. The uptake processes by vegetation and the soil are described by a Deardorff-typee soil-vegetation-atmosphere transfer scheme. The model results show that especially the dry deposition fluxes of the reactive nitrogen compounds are not only influenced by micrometeorological and plant-physiological parameters, but also strongly affected by chemical reactions. In most cases, the fluxes of these trace constituents vary strongly with height and often show a change of direction. These flux result s differ considerably from those derived with the constant flux approximation, sometimes by up to several hundred percent. Thus, in such cases the most widely used "big leaf" multiple resistance approach which is based on the constant flux approximation seems to be inappropriate for deriving dry deposition fluxes and deposition velocities of reactive nitrogen compounds.
  • Publication
    On the dry deposition of ozone and reactive nitrogen species
    ( 1995)
    Kramm, G.
    ;
    Dlugi, R.
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    Dollard, G.J.
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    Foken, T.
    ;
    Mölders, N.
    ;
    Müller, H.
    ;
    Seiler, W.
    ;
    Sievering, H.
    Dry deposition of ozone and reactive nitrogen species, such as NO, NO2, NO3, N2O5, HNO3, NH3 and NH4NO3, is examined in the context of numerical methods. These methods are based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat, and matter near the Earth's surface, where chemical reactions among these trace species are considered. The fluxes in the turbulent region of the atmospheric surface layer are parameterized by first-order closure principles. The uptake processes by vegetation and the soil are described by a Deardorff-type soil-vegetation-atmosphere transfer scheme. As in the case of HNO3 and NH3 the resistance of the system vegetation-soil against uptake of matter seems to be of minor importance, parameterization approaches for the more important transfer resistances of the interfacial sublayer adjacent to the surface are evaluated. The model results show that especially the dry deposition fluxes of reactive nitrogen species are not only influenced by micrometeorological and plant-physiological parameters, but also strongly affected by chemical reactions. In most cases, the fluxes of these trace constituents vary strongly with height and often show a change of direction. These flux results differ considerably from those derived with the constant flux approximation, sometimes up to several hundred percent. Thus, in such cases the most widely used "big leaf" multiple resistance approach which is based on the constant flux approximation seems to be inappropriate for deriving dry deposition fluxes and deposition velocities of reactive nitrogen species.
  • Publication
    Role of methane and nitrous oxide in climate change
    ( 1995)
    Rennenberg, H.
    ;
    Wassmann, R.
    ;
    Papen, H.
    ;
    Seiler, W.