W. Behnke

University of Lyon, Lyons, Rhône-Alpes, France

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Publications (36)37.71 Total impact

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    ChemPhysChem 10/2010; 11(14):3059-62. · 3.35 Impact Factor
  • Wolfgang Behnke, Cornelius Zetzsch
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    ABSTRACT: We observed bromine explosions (a fast production of atomic Br and Cl under tropospheric conditions) in various smog chamber experiments in Teflon bags at room temperature at a relative humidity of about 80% in the presence of NaCl/NaBr-aerosol, simulated sunlight and ozone (200 - 400 ppb). Time profiles of ozone and hydrocarbons (HCs: n-butane, 2,2-dimethylbutane, tetramethylbutane and toluene, initially about 2 ppb each) were monitored to determine concentrations and source strengths of OH radicals, atomic Cl and Br and the corresponding time profiles of BrCl and Br2 as their photolytic precursors. The number and size of aerosols are measured as well as their chemical composition (Br-, Cl- and oxalic acid). Full records of raw data from the smog chamber runs are available at www.eurochamp.org for potential users. Chemical box model calculations deliver concentrations of various intermediates, such as aldehydes, HO2 and RO2 radicals and the inorganic halogen compounds ClO, BrO, HOCl and HOBr, where HOBr from O3 + Br- => BrO- + O2 in the aqueous/adsorbed phase induces the following gas-phase/ heterogeneous chain reaction Br + O3 => BrO + O2(1) BrO + HO2 => HOBr + O2(2a) HOBr + (Aerosol) => HOBrad(3) Surface-adsorbed HOBr reacts with Br- or Cl- to produce Br2 or BrCl, both of which are released and photolysed. Formation of Br2 should prevail up to Cl-/Br- -ratios of about 104 (Fickert, S., J.W. Adams, J.N. Crowley, J. Geophys. Res., D104, 23719-23727, 1999). A maximum of this ratio is reached about 30 minutes after the beginning and decreases during the next hours - probably by reaction of Br2 with oxalate and absorption of HBr, formed from the reaction of Br with aldehydes. Parallel to chain reaction (1)-(3) a chain reaction replacing Br by Cl seems possible but can not be realized, since the main sink of atomic Cl is its reaction with hydrocarbons - leading to chain termination - in contrast to atomic Br (ratio of rates: kCl[O3]/kCl[HC] ~ 0.1; kBr[O3]/kBr[toluene] ~ 100). Formation of aldehydes (R-CHO) interferes with the chain reaction (1) - (3) markedly, since kBr[O3] ≈kBr[R-CHO]. The chain reaction is limited by availability of ozone (degradation of HCs by atomic Cl stops completely with vanishing ozone), of HO2 (HCs are required to form HO2) and of aerosol. The central question is: will sufficient HO2 be formed from degradation of HCs to explain the magnitude of the formed Br2 and BrCl in our experiments? We found that the formation of HO2 should be by a factor of 2-4 larger to explain the formation of Br2 and BrCl. Which other sources for the formation of HOBr besides reaction (2a) are then available? The rate of CH3O2with BrO is 25% of that with HO2 (Enami, S.; Yamanaka, T.; Nakayama, T.; Hashimoto, S.; Kawasaki, M.; Shallcross, D.E.; Nakano, Y.; Ishiwata, T., J. Phys. Chem. A, 11, 3342 - 3348, 2007), suggesting that other RO2 radicals must contribute. In our model calculations we use this rate constant for all RO2 radicals to obtain reasonable agreement between the produced HOBr and the formed BrCl and Br2 necessary for our experimental degradation results. So reaction scheme (1) - (3) should be completed by: BrO + RO2 => HOBr + products (2b) The German Science Foundation (DFG) supported this research in unit 783 (HALOPROC).
    05/2010;
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 29(20).
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 29(12).
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    ABSTRACT: Experiments to investigate the release of reactive halogen species from sea-salt aerosol and the influence of organic matter were performed in an aerosol smog-chamber (3500 l), made of Teflon film (FEP 200A, Dupont). Smog chamber facilities at lowered temperature (coolable down to -25°C) enable us to simulate these reactions under polar, tropospheric conditions. First experiments were performed to investigate the production of atomic Br and Cl without the impact of organic aerosol. Br and Cl play an important role in atmospheric ozone depletion, particularly regarding ozone depletion events (bromine explosion) during polar spring. In these studies, the aerosol was generated by atomizing salt solutions containing the typical Br/Cl ratio of 1/660 in seawater by an ultrasonic nebulizer and increasing the Br content up to sixfold. To ensure the aqueous surface of the aerosol, the experiments were performed at relative humidities above 76%. We determined the atomic Cl and OH-radical concentrations from the simultaneous consumption of four reference hydrocarbons. The Br-radical concentration was calculated on the basis of ozone depletion. Organic aerosol may take part in these reaction cycles by halogenation and production of volatile organic halogens. Further experiments are planned to add organic aerosol for mechanistic and kinetic studies on the influence of secondary organic aerosols (SOA) and humic-like substances (HULIS) on bromine explosion. The formation of the secondary organic aerosol and the determination of possible halogenated gaseous and solid organic products will be studied using longpath-FTIR, DRIFTS, ATR-FTIR, GC-FID, GC-ECD, GC-MS, TPD-MS and DMA-CNC.
    AGU Fall Meeting Abstracts. 12/2008;
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    ABSTRACT: This work presents the heterogeneous kinetics of the reaction of CH3SCH3 (dimethyl sulphide, DMS) with O3 (ozone) in aqueous solutions of different ionic strengths (0, 0.1 and 1.0M NaCl) using the wetted-wall flowtube (WWFT) technique. Henry's law coefficients of DMS on pure water and on different concentrations of NaCl (0.1M - 4.0M) in the WWFT from UV spectrophotometric measurements of DMS in the gas phase, using a numerical transport model of phase exchange, were determined to be H ±s (M atm-1) = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4 K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 291 K, showing a significant effect of ionic strength, m, on the solubility of DMS according to the equation ln (H/M atm-1) = 4061 T-1 - 0.052 m2 - 50.9 m T-1 - 14.0. At concentrations of DMS(liq) above 50 mM, UV spectrophotometry of both O3(gas) and DMS(gas) enables us to observe simultaneously the reactive uptake of O3 on DMS solution and the gas-liquid equilibration of DMS along the WWFT. The uptake coefficient, g (gamma), of O3 on aqueous solutions of DMS, varying between 1 and 15·10-6, showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution). The uptake coefficient was smaller on NaCl solution in accord with the lower solubility of O3. The heterogeneous reaction of O3(gas) with DMS(liq) was evaluated from the observations of the second order rate constant (kII) for the homogeneous aqueous reaction O3(liq) + DMS(liq) using a numerical model of radial diffusion and reactive penetration, leading to kII ± D kII (in units of 108 M-1 s-1) = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on kII, that was determined for 0.1M NaCl, leading to kII ± D kII (108 M-1 s-1) = 3.2±1.0 at 288 K, 1.7±0.5 at 282 K and 1.3±0.4 at 276 K, and for 1.0M NaCl, leading to 3.2±1.0 at 288 K, 1.3±0.4 at 282 K and 1.2±0.4 at 276 K, where the error limits are estimated from the output of the model calculations, taking the variability of individual runs at various DMS levels into account.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2003; · 5.51 Impact Factor
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    ABSTRACT: This work presents the heterogeneous kinetics of the reaction of CH<sub>3</sub>SCH<sub>3</sub> (dimethyl sulphide, DMS) with O<sub>3</sub> (ozone) in aqueous solutions of different ionic strengths (0, 0.1 and 1.0M NaCl) using the wetted-wall flowtube (WWFT) technique. Henry's law coefficients of DMS on pure water and on different concentrations of NaCl (0.1M - 4.0M) in the WWFT from UV spectrophotometric measurements of DMS in the gas phase, using a numerical transport model of phase exchange, were determined to be H ± s (M atm<sup>-1</sup>) = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4 K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 291 K, showing a significant effect of ionic strength, m , on the solubility of DMS according to the equation ln (H/M atm<sup>-1</sup>) = 4061 T<sup>-1</sup> - 0.052 m <sup>2</sup> - 50.9 m T<sup>-1</sup> - 14.0. At concentrations of DMS<sub>(liq)</sub> above 50 m M, UV spectrophotometry of both O<sub>3(gas)</sub> and DMS<sub>(gas)</sub> enables us to observe simultaneously the reactive uptake of O<sub>3</sub> on DMS solution and the gas-liquid equilibration of DMS along the WWFT. The uptake coefficient, g (gamma), of O<sub>3</sub> on aqueous solutions of DMS, varying between 1 and 15·10<sup>-6</sup>, showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution). The uptake coefficient was smaller on NaCl solution in accord with the lower solubility of O<sub>3</sub>. The heterogeneous reaction of O<sub>3(gas)</sub> with DMS<sub>(liq)</sub> was evaluated from the observations of the second order rate constant (k<sup>II</sup>) for the homogeneous aqueous reaction O<sub>3(liq) </sub> + DMS<sub>(liq)</sub> using a numerical model of radial diffusion and reactive penetration, leading to k<sup>II</sup> ± D k<sup>II</sup> (in units of 10<sup>8</sup> M<sup>-1</sup> s<sup>-1</sup>) = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on k<sup>II</sup>, that was determined for 0.1M NaCl, leading to k<sup>II </sup>± D k<sup>II</sup> (10<sup>8</sup> M<sup>-1</sup> s<sup>-1</sup>) = 3.2±1.0 at 288 K, 1.7±0.5 at 282 K and 1.3±0.4 at 276 K, and for 1.0M NaCl, leading to 3.2±1.0 at 288 K, 1.3±0.4 at 282 K and 1.2±0.4 at 276 K, where the error limits are estimated from the output of the model calculations, taking the variability of individual runs at various DMS levels into account.
    Atmospheric Chemistry and Physics. 01/2003;
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    Wolfgang Behnke, Manfred Elend, Cornelius Zetzsch
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    ABSTRACT: 1. Summary The effeciency of halogen activation from artificial sea -spray aerosol (NaBr/NaCl) was investigated in smog-chamber experiments and by model calculations. The uptake coefficient γ of HOBr on wet NaCl/NaBr aerosol at pH 3.5 - 4 was found to be (3±1.5) · 10-3.
    01/2002;
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    ABSTRACT: The activation of Br- and Cl- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O3, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br- to the aerosol, the chain reaction: Br + O3 BrO, BrO + HO2 HOBr, HOBr HOBr(aq), HOBr(aq) + H+ + Br- Br2 (6), HOBr(aq) + H+ + Cl- BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br-/Cl- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NOx or SO2). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br2 by oxalic acid was observed to occur through a two-step mechanism: HC2O4 - + Br2 Br- + BrC2O4H (k22, k-22), BrC2O4H Br- + H+ + 2 CO2 (23) with the following rate constants and ratios of rate constants, k 2: k22k-23 / k-22 = (2.9 0.3) 10-4 s-1, k-22 / k-23 = 7000 3000 13000 M-1, k22 = 2 -1 4 M-1 s-1, and k-23 > 0.1 s-1, k-22 > 600 M-1 s-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.
    Journal of Atmospheric Chemistry 01/1999; 34(1):87-99. · 1.33 Impact Factor
  • EC/DG XII Cluster 4, Copenhaben, Denmark; 08/1998
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    ABSTRACT: The heterogeneous reactions leading to formation and loss of BrNO2 on salt solutions as a model substrate for atmospheric sea salt aerosol are investigated. Further to the reaction of ClNO2 with bromide solutions, the reaction of Br2 with nitrite solution was found to be a convenient method for the synthesis of BrNO2. We measured the temperature-dependent lifetime of BrNO2 in a quartz cell and obtained the activation energy EA = 89 ± 9 kJ/mol for the unimolecular decay at atmospheric pressure. The reactive uptake of BrNO2 and ClNO2 on water and aqueous solutions was determined using a wetted-wall flow tube technique. We observed the reactions Br2 + NO2- ↔ BrNO2 + Br-, Cl2 + NO2- → ClNO2 + Cl-, and the net reaction ClNO2 + Br- ↔ BrNO2 + Cl-. BrNO2 and ClNO2 both react with NO2- to release NO2 into the gas phase. Observed concentration profiles in the gas phase and in solution can be described qualitatively by a numerical model of the diffusion and reaction processes in the experimental setup.
    The Journal of Physical Chemistry A 02/1998; 102(8). · 2.77 Impact Factor
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    Environmental Science and Pollution Research 02/1998; 5(3):119-96. · 2.76 Impact Factor
  • Journal of Physical Chemistry A - J PHYS CHEM A. 01/1998; 102(8):1329-1337.
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    ABSTRACT: The uptake kinetics of nitrosyl chloride (NOCl) by aqueous solutions has been measured as a function of temperature, using two different techniques, i.e., the wetted-wall at atmospheric and reduced pressure and the droplet train flow tubes, both techniques being combined with FTIR and HPLC detection. Uptake coefficients, which were shown to be slightly temperature dependent, range from 0.012 to 0.0058 for temperatures between 273 and 293 K. The production of HONO was observed from the hydrolysis of NOCl, and its yield in the gas phase is in agreement with the Henry's law constant of nitrous acid. The uptake of NOCl was also studied on solutions containing HCl, NaCl, and NaOH. Only the latter affected the uptake kinetics, probably through a nucleophilic reaction with OH-. The observed kinetics are shown to be consistent with a lower limit of 0.03 for the mass accommodation coefficient. These results suggest that heterogeneous removal of NOCl is very efficient, meaning that this compound is not expected to be a significant precursor of atomic Cl in the atmosphere. The Henry's law constant for NOCl was observed to be greater than 0.05 mol L-1 atm-1.
    The Journal of Physical Chemistry A 12/1997; 101(49). · 2.77 Impact Factor
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    ABSTRACT: The chemistry of N2O5 on liquid NaCl aerosols or bulk NaCl solutions was studied at 291 K by aerosol smog chamber and wetted-wall flow tube experiments. The uptake of N2O5 on deliquescent aerosol was obtained to be (3.2+/-0.2)×10-2 (1sigma error) from the aerosol experiments. In the wetted-wall flow tube we observed that nitryl chloride (ClNO2) is the main product of the reaction at NaCl concentrations larger than approximately 0.5M and almost the only product at concentrations larger than 1M. The ClNO2 yield does not depend linearly on the NaCl concentration, especially at small sodium chloride concentrations (i.e., smaller than 1M). It appeared that a simple mechanism where N2O5 undergoes two reaction channels (hydrolysis and reaction with Cl-) is unable to explain the observed concentration dependence of the product yield. We propose that N2O5 dissociates to NO2+ and NO3- (rate constant k1>104s-1) mainly. The directly hydrolysis of N2O5 (k3[H2O]) is less than 20% of the total reaction. NO2+ reacts with water to form 2H+ and NO3- (k5) or with Cl- to form ClNO2 (k4). Neglecting the influence of ionic strength we evaluate k4/k5 to be 836+/-32 (1sigma error). Using the wetted-wall flow tube technique, we studied the uptake of nitryl chloride by aqueous solutions containing NaCl. We observed that the uptake coefficient gamma decreased from (4.84+/-0.13)×10-6 on pure water to (0.27+/-0.02)×10-6 on a 4.6M NaCl solution. The sharp decrease of gamma with increasing salt concentrations is evidence of reversible hydrolysis. ClNO2 dissociates to Cl-+NO2+ (k6). In the absence of Cl- we evaluate H.k61/2 to be 0.44+/-0.01molL-1atm-1s-1/2. Finally, we discuss that atomic Cl from photolysis of ClNO2 may play a role in the marine boundary layer at high northern latitudes.
    Journal of Geophysical Research 01/1997; 102:3795-3804. · 3.17 Impact Factor
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    ABSTRACT: A method for the synthesis of gaseous BrNO2 at concentrations of the order of 10-9 mol/cm3 at atmospheric pressure is described, based on the heterogeneous reaction of ClNO2 with aqueous bromide solutions. We measured the gas-phase infrared absorption cross sections in the range 700−1800 cm-1. The matrix isolation spectrum was recorded for identification by comparison with literature data.
    The Journal of Physical Chemistry. 01/1996; 100(41):16447-16450.
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    ABSTRACT: The uptake of nitryl chloride ClNO2 by pure water and NaI solutions was studied as a function of temperature in the range from 268 to 279 K with the droplet train technique. An upper limit of 10−5 was derived for the uptake on pure water, while the uptake rate was observed to be greatly enhanced in the presence of 10−3–10−2 M iodide, yielding uptake coefficients in the range from 1.1 × 10−3 to 6.6 × 10−3. This enhancement is a consequence of a reaction between I− and ClNO2 where we suggest that a transfer of Cl+ to iodide is involved. We also suggest that bulk kinetics alone is unable to describe the measured uptake rate which is influenced by surface reactions. These results show that heterogeneous chemistry in concentrated aerosols may play an important role for the fate of ClNO2, and may affect the concentration of atomic chlorine in the marine boundary layer.
    Geophysical Research Letters 01/1995; 22(12):1505-1508. · 3.98 Impact Factor
  • Journal of Aerosol Science 01/1995; 26. · 2.69 Impact Factor
  • W BEHNKE, V SCHEER, C ZETZSCH
    Journal of Aerosol Science - J AEROSOL SCI. 01/1994; 25:277-278.
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    ABSTRACT: Using the droplet train technique, the uptake of NâOâ by NaCl solution and pure water was studied as a function of temperature in the 262-278 K range. The NâOâ uptake coefficients on pure water decrease from 0.03 to 0.013 with increasing temperature. With the NaCl solution, there was a lower nitrate yield, indicating that nitrogen compounds are formed after the NâOâ uptake by reactions with NaCl. The NaCl uptake coefficient is greater than pure water, so NâOâ may be reaction-controlled. 38 refs., 7 figs., 1 tab.
    The Journal of Physical Chemistry. 01/1994; 98(35):8780-8784.