Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    NOx or VOC limitation in East German ozone Plumes?
    ( 2000)
    Klemm, O.
    ;
    Stockwell, W.R.
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    Schlager, H.
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    Krautstrunk, M.
    The ozone forming potential of VOCs and NO sub x for plumes observed from several cities and a power plant in eastern Germany was investigated. A closed box model with a gas phase photochemical reaction mechanism was employed to simulate several scenarios based upon aircraft observations. In several of the scenarios, the initial concentrations of NO sub x VOCs, and SO2, were reduced to study the factors limiting the O3 production. Ozone production was limited by the initial VOC concentrations for all of the simulated plumes. Higher O3 concentrations were produced with reduced initial NO sub x. In one sample with high SO2 mixing ratios (> 100 ppb), SO2 was also identified as a significant contributor to the production of O3.
  • Publication
    Temporal and spatial variation of sulfur-gas-transfer between coastal marine sediments and the atmosphere
    ( 1999)
    Bodenbender, J.
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    Wassmann, R.
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    Papen, H.
    ;
    Rennenberg, H.
    The spatial and temporal variability of sulfur gas fluxes (H2S, COS, CH3SH, DMS, and CS2) at the sediment-air interface were studied in the intertidal Wadden Sea area of Sylt-Roemoe (Germany/Denmark) during eight measuring campaigns between June 1991 and September 1994. Measurements were performed mainly at four sites in a sheltered intertidal bay of approximately 6 km2 (Königshafen) and discontinuously in a wider range of the 400 km2 Sylt-Roemoe tidal flat area. In situ fluxes of the S-gases were determined by a dynamic chamber technique focusing on dry sediment periods. Additional experiments were conducted in order to determine changes in S-gas concentrations in the sediment between the surface and 70 cm depth. In most cases H2S was the dominant S-gas emitted from the sediment to the atmosphere, contributing up to 70% of the total S-emission at this interface. Mean H2S emission rates ranged between 0.07 and 9.95 mu g S m(exp -2) h(exp -1). Both emission rates and relative contribution of H, S were lowest from fine sand and highest from muddy sites. Diurnal variation of H2S emission was evident in summer and fall with up to 10-fold higher rates during night than during the day. Distinct seasonal variation of H2S-transfer between the sediment and the atmosphere was observed with higher emission rates in the summer than in spring or fall. The emission of H2S to the atmosphere was smaller by a factor of 1600-26 000 than the H2S produced from sulfate reduction. Apparently, the efficiency by which H2S produced in the sediment is retained and reoxidized by biogeochemical sediment processes is extremely high. Carbonyl sulfide (COS) was emitted with relatively constant rates in space and time with mean flux rates ranging between 0.24 and 2.0 mu g S m(exp -2) h(exp -1). Carbon disulfide emission rates were comparable to those of COS and varied between 0.3 and 2.23 mu g S m(exp - 2) h(exp -1). DMS played a minor role in the S-gas transfer from uncovered sediment areas contributing between 3.1 and 23% to total S-emission from the sediment to the atmosphere.
  • Publication
    On the spatial distribution and seasonal variation of lower-troposphere ozone over Europe
    ( 1997)
    Scheel, H.E.
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    Areskoug, H.
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    Geiß, H.
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    Gomiscek, B.
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    Granby, K.
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    Haszpra, L.
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    Klasinc, L.
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    Kley, D.
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    Laurila, T.
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    Lindskog, A.
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    Roemer, M.
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    Schmitt, R.
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    Simmonds, P.
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    Solberg, S.
    ;
    Toupance, G.
    Surface ozone data from 25 European low-altitude sites and mountain sites located between 79 deg N and 28 deg N were studied. The analysis covered the time period March 1989-February 1993. Average summer and winter O3 concentrations in the boundary layer over the continent gave rise to gradients that were strongest in the north-west to south-east direction and west-east direction, respectively. Wintertime O3 ranged from 19 to 27 ppb over the continent, compared to about 32 ppb at the western border, while for summer the continental O3 values ranged between 39 and 56 ppb and the oceanic mixing ratios were around 37 ppb. In the lower free troposphere average wintertime O3 mixing ratios were around 38 ppb, with only an 8 ppb difference between 28 deg N and 79 deg N. For summer the average O3 levels decreased from about 55 ppb over Central Europe to 32 ppb at 79 deg N. In addition, O3 and Ox (= O3 + NO2) in polluted and clean air were compared. The amplitudes of the seasonal ozone variatio ns increased in the north-west to south-east direction, while the time of the annual maximum was shifted from spring (at the northerly sites) to late summer (at sites in Austria and Hungary), which reflected the contribution of photochemical ozone production in the lower parts of the troposphere.
  • Publication
    Regional and global tropopause fold occurence and related ozone flux across the tropopause
    ( 1997)
    Beekmann, M.
    ;
    Ancellet, G.
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    Blonsky, S.
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    Muer, D. de
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    Ebel, A.
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    Elbern, H.
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    Hendricks, J.
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    Kowol, J.
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    Mancier, C.
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    Sladkovic, R.
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    Smit, H.G.J.
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    Speth, P.
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    Trickl, T.
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    Haver, P. van
    This paper gives a synthesis of three algorithms to detect the presence of tropopause folds from vertical ozone/radio-sounding profiles and from meteorological analysis. Also an algorithm to identify injection of stratospheric air into the lower troposphere from ozone/7 beryllium time series is presented. Differences in the results obtained from the algorithms are observed and discussed with respect to the criteria for fold detection and input data used. Spatial gradients in the obtained folding frequencies are made evident on a global scale from the algorithm based on meteorological analysis (Q-vector/potential vorticity) and probably also on a regional European scale from algorithms both based meteorological analyses and on ozone/PTU soundings. The observed seasonal variation of folding occurrence is rather flat except during summer when also some differences appear between the algorithms. By combining the folding frequencies with literature estimates of the cross-tropopause ozone tr ansfer in single folding events, an average stratospheric ozone influx into the troposphere of 5.7 ¤ 1.3 x 10(exp 10) mol. cm(-2) s(-1) is obtained for the Northern hemisphere and 12 ¤ 2.7 x 10(exp 10) mol. cm(-2) s(-1) for Western Europe. Potential additional contributions due to other stratospheretroposphere exchange processes than folds are not yet included in these estimates. Finally, the link between statistics from ozone/7 beryllium data and folding statistics is briefly discussed.
  • Publication
    Structures of UV-B induced sunscreen pigments of the Scots Pine (Pinus sylvestris L.)
    ( 1995)
    Jungblut, T.P.
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    Schnitzler, J.-P.
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    Heller, W.
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    Hertkorn, N.
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    Metzger, J.W.
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    Szymaczak, W.
    ;
    Sandermann, H.
  • Publication
    Modelling of the vertical fluxes of nitric acid, ammonia, and ammonium nitrate
    ( 1994)
    Kramm, G.
    ;
    Dlugi, R.
    Results from numerical investigations regarding the exchange of HNO3, NH3, and NH4NO3 between the atmosphere and the biosphere are presented. The investigations were performed with a modified inferential method which is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these nitrogen compounds. This modified inferential method calculates the micrometeorological quantities (such as the friction velocity and the fluxes of sensible and latent heat), the height-invariant fluxes of the composed chemically conservative trace species with 'group' concentrations c(1)= (HNO3) + (NH4NO3) (total nitrate), c(2)=(NH3) + (NH4NO3) (total ammonia), and c(3) = (HNO3) - (NH3) as well as the fluxes of the 'individual' nitrogen compounds. The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The modified i nferential method requires only the data of wind velocity, temperature, humidity and concentrations (HNO3, NH3, and NH4NO3) measured at a reference height by stations of a monitoring network.
  • Publication
    Replacing gram-equivalents and normalities
    ( 1994)
    Mills, I.
    ;
    Cvitas, T.
    The article shows that the equiv., equiv. wt., and the normality of a soln. as a measure of concn., are ambiguous and out-dated concepts, which are displaced in the language of modern chem. by the mole, the mol. wt., and the concn. in mole/L.
  • Publication
    Hydroperoxides in the Marine Troposphere over the Atlantic Ocean
    ( 1994)
    Slemr, F.
    ;
    Tremmel, H.G.
    Hydrogen peroxide (H2O2) and organic hydroperoxides (ROOH) were measured on board of the RV Polarstern during its cruise across the Atlantic Ocean from 20 October to 12 November 1990 (54 deg N to 51 deg S latitude) by the enzyme fluorometric method. The H2O2 mixing ratio varied from below the detection limit of about 0.12 ppbv up to 3.89 ppbv, showing a latitudinal dependence with generally higher values around the equator and decreasing values poleward. The shape of the latitudinal H2O2 distribution agrees well with an analytical steady state expression for H2O2 using the measured H2O and O3 distribution and a wind dependent H2O2 deposition rate. The ROOH mixing ratio varied from below the detection limit of about 0.08 ppbv up to 1.25 ppbv with qualitatively the same latitudinal dependence as H2O2. The observed ratio ROOH/(ROOH + H2O2) varied between 0.17 and 0.98 showing higher values at the lowest H2O2 mixing ratios at high latitudes. The measured H2O2 mixing ratio shows a significa nt diurnal variation with a maximum around 14:00 local time, explicable by a superposition of the photochemical H2O2 production with a constant H2O2 deposition rate. Four independent estimations of the average effective H2O2 deposition rate inferred from the H2O2 decrease in the night, from the midday H2O2 production deficit (as derived from comparison with a photochemical model and from the daily ozone loss), and from the offset in the latitudinal H2O2 distribution, were consistent. An episode of maximum H2O2 concentration suggests the possibility of its formation in clouds.
  • Publication
    The effect of gas-phase chemistry on aqueous-phase sulfur dioxide oxidation rates
    ( 1994)
    Stockwell, W.R.
    The rates and mechanisms of both gas and liquid phase reactions for the oxidation of sulfur dioxide play an important role in the production of atmospheric acids and aerosol particles. Rhode et al. (198 1) concluded that sulfate production rates were highly non-linear functions of sulfur dioxide emission rates. Their modelling study used an HO(x) termination mechanism for the HO-SO2 reaction in the gas-phase. Stockwell and Calvert (1983) determined that one of the products of the overall reaction of HO with sulfur dioxide was an HO2 radical. The National Research Council (1983) using a version of the Rhode et al. (1981) model modified to include HO2 production from the HO-SO2 reaction concluded that sulfate production becomes much more linear with respect to reductions in sulfur dioxide emissions. However, the cause of this increased linearity was not explained by the National Research Council report. It is demonstrated that the increased linearity is due to the coupling of gas-phase a nd aqueous-phase chemistry. The gas-phase sulfur dioxide oxidation mechanism has a very significant effect on hydrogen perodide production rates.