J. Meinen

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (16)27.59 Total impact

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    ABSTRACT: The detection of atmospheric NO3 radicals is still challenging owing to its low mixing ratios (�1 to 300 pptv) in the troposphere. While long-path differential optical absorption spectroscopy (DOAS) is a well established NO3 detection approach for over 25 yr, 5 newly sensitive techniques have been developed in the past decade. This publication outlines the results of the first comprehensive intercomparison of seven instruments developed for the spectroscopic detection of tropospheric NO3. Four instruments were based on cavity ring-down spectroscopy (CRDS), two utilised open-path cavity enhanced absorption spectroscopy (CEAS), and one applied “classical” long-path DOAS. 10 The intercomparison campaign “NO3Comp” was held at the atmosphere simulation chamber SAPHIR in J¨ ulich (Germany) in June 2007. Twelve experiments were performed in the well mixed chamber for variable concentrations of NO3, N2O5, NO2, hydrocarbons, and water vapour, in the absence and in the presence of inorganic or organic aerosol. The overall precision of the cavity instruments varied between 0.5 and 15 5 pptv for integration times of 1 s to 5min; that of the DOAS instrument was 9 pptv for an acquisition time of 1 min. The NO3 data of all instruments correlated excellently with the NOAA-CRDS instrument, which was selected as the common reference because of its superb sensitivity, high time resolution, and most comprehensive data coverage. The median of the coefficient of determination (r2) over all experiments of the campaign (60 20 correlations) is r2 =0.981 (25th/75th percentiles: 0.949/0.994; min/max: 0.540/0.999). The linear regression analysis of the campaign data set yielded very small intercepts (1.2±5.3 pptv) and the average slope of the regression lines was close to unity (1.02, min: 0.72, max: 1.36). The deviation of individual regression slopes from unity was always within the combined accuracies of each instrument pair. The very good cor- respondence between the NO3 measurements by all instruments for aerosol-free experiments indicates that the losses of NO3 in the inlet of the instruments were determined reliably by the participants for the corresponding conditions. In the presence of inorganic or organic aerosol, however, differences in the measured NO3 mixing ratios were detectable among the instruments. In individual experiments the discrepancies increased with time, pointing to additional NO3 radical losses by aerosol deposited onto the inlet walls of the instruments. Instruments using DOAS analyses showed no significant effect of aerosol on the detection of NO3. No hint of a cross interference of NO2 5 was found. The effect of non-Lambert–Beer behaviour of water vapour absorption lines on the accuracy of the NO3 detection by broadband techniques was small and well controlled. The NO3Comp campaign demonstrated the high quality, reliability and robustness of performance of current state-of-the-art instrumentation for NO3 detection.
    Atmospheric Measurement Techniques 01/2013; 6:1111-1140. · 3.21 Impact Factor
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    ABSTRACT: We present direct optical extinction measurements on free size filtered iron oxide nanoparticles in the size range between 3 nm and 10 nm diameter. The high number density of nanoparticles required for the cavity enhanced absorption spectroscopy (CEAS) measurements was achieved by combining a high intensity plasma synthesis source of iron oxide particles with an aerodynamic lens inlet into the vacuum system and radiofrequency particle guiding and storage devices. The extinction cross sections can be quantitatively explained using the bulk optical constants of hematite, which may exist in the form of nanoparticles in the mesosphere.
    Applied Physics B 09/2012; 108(3). · 1.63 Impact Factor
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    ABSTRACT: We have explored the spatial distribution of an ion cloud trapped in a linear octopole radio-frequency (rf) ion trap. The two-dimensional distribution of the column density of stored silver dimer cations was measured via photofragment-ion yields as a function of the position of the incident laser beam over the transverse cross section of the trap. The profile of the ion distribution was found to be dependent on the number of loaded ions. Under high ion-loading conditions with a significant space-charge effect, ions form a ring profile with a maximum at the outer region of the trap, whereas they are localized near the center axis region at low loading of the ions. These results are explained quantitatively by a model calculation based on equilibrium between the space-charge-induced potential and the effective potential of the multipole rf field. The maximum adiabaticity parameter \eta_max is estimated to be about 0.13 for the high ion-density condition in the present octopole ion trap, which is lower than typical values reported for low ion densities; this is probably due to additional instability caused by the space charge.
    Physical Review A 03/2012; 85(5). · 2.99 Impact Factor
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    ABSTRACT: Optical-feedback cavity enhanced absorption spectroscopy (OF-CEAS) is a very sensitive technique for the detection of trace amounts of gaseous absorbers. The most crucial parameter in an OF-CEAS setup is the optical phase of the light fed back into the laser source, which is usually controlled by the position of a piezo driven mirror. Various approaches for the analysis of the cavity transmitted light with respect to feedback-phase are presented, and tested on simulated phase and frequency dependent cavity transmission. Finally, we present the performance of a digital signal processor based regulator—employing one of these approaches—in a real OF-CEAS experiment. The results of the simulation show that several algorithms are well suited for the task of control signal generation. They confirm also that with the presented approach, a mode by mode correction of the feedback-phase is possible. Consequently, a regulatory bandwidth of 37 Hz was achieved. This maximum control frequency was limited by the piezo system.
    Applied Physics B 02/2011; 106(2). · 1.63 Impact Factor
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    ABSTRACT: A novel instrument is presented, which permits studies on singly charged free nanoparticles in the diameter range from 1 to 30 nm using synchrotron radiation in the soft x-ray regime. It consists of a high pressure nanoparticle source, a high efficiency nanoparticle beam inlet, and an electron time-of-flight spectrometer suitable for probing surface and bulk properties of free, levitated nanoparticles. We show results from x-ray photoelectron spectroscopy study near the Si L(3,2)-edge on 8.2 nm SiO(2) particles prepared in a nanoparticle beam. The possible use of this apparatus regarding chemical reactions on the surface of nanometer-sized particles is highlighted. This approach has the potential to be exploited for process studies on heterogeneous atmospheric chemistry.
    The Review of scientific instruments 08/2010; 81(8):085107. · 1.58 Impact Factor
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    ABSTRACT: We present an experimental setup that allows the injection of charged nanoparticles in a diameter range of 3–15 nm into a vacuum chamber and their storage there in an electrodynamic cage. The nanoparticle density in the trap is limited by space charge and can be several orders of magnitude higher than in a free nanoparticle beam. The setup provides for the first time a tool for the application of advanced techniques of spectroscopy to free nanoparticles in this size range. It consists of a combination of (1) a plasma discharge nanoparticle source that generates a high density of nanoparticles of various composition suspended in helium carrier gas at a pressure of about 10–150 mbar, (2) an aerodynamic lens optimized for small particles (diameter 3–15 nm) that forms a well-collimated beam of charged nanoparticles and focuses it into (3) an octopole ion trap operated at low frequencies and filled with helium buffer gas at 10−2 mbar in order to moderate and store the nanoparticles at densities of more than 107 cm−3.
    Aerosol Science and Technology 04/2010; 44(4):316-328. · 3.16 Impact Factor
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    ABSTRACT: No abstract available.
    Atmospheric Measurement Techniques. 01/2010;
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    ABSTRACT: Cavity enhanced methods in absorption spectroscopy have seen a considerable increase in popularity during the past decade. Especially Cavity Enhanced Absorption Spectroscopy (CEAS) established itself in atmospheric trace gas detection by providing tens of kilometers of effective light path length using a cavity as short as 1 m. In this paper we report on the construction and testing of a compact and power efficient light emitting diode based broadband Cavity Enhanced Differential Optical Absorption Spectrometer (CE-DOAS) for in situ observation of atmospheric NO3. This device combines the small size of the cavity with the advantages of the DOAS approach in terms of sensitivity, specificity and insensivity to intensity fluctuations of the light source. In particular, no selective removal of the analyte (here NO3) is necessary for calibration of the instrument if appropriate corrections are applied to the CEAS theory. Therefore the CE-DOAS technique can – in principle – measure any gas detectable by DOAS. We will discuss the advantages of using a light emitting diode (LED) as light source particularly the precautions which have to be considered for the use of LEDs with a broad wavelength range. The instrument was tested in the lab by detecting NO3 formed by mixing of NO2 and O3 in air. It was then compared to other trace gas detection techniques in an intercomparison campaign in the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich at NO3 concentrations as low as 6.3 ppt.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2010; · 5.30 Impact Factor
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    Atmospheric Measurement Techniques 01/2010; 3(1):127-128. · 3.21 Impact Factor
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    ABSTRACT: The IPCC AR4 points out the important role of aerosol in the radiation budget of the earth. In the model prediction, direct and indirect contribution of the atmospheric aerosol causes a net cooling of the earth. Understanding the fundamental physical and chemical processes of heterogeneous nucleation of water on nanoparticles could help improving the models. On our poster we present the first stage of the TRAPS apparatus (Trapped Reactive Atmospheric Particle Spectrometer). The apparatus comprises as nanoparticle sources atomizers, electrospray and plasma reactors in order to produce nanoparticle sizes from 20-50nm, 10-20nm and 5-10nm respectively. The nanoparticles are dispersed in helium as carrier gas at high pressure. After passing a critical orifice into rough vacuum a tunable aerodynamic lens is used to focus the particles into a differential pumping stage. We put high effort in optimizing the aerodynamic lens for particle beams close to the diffusion limit by CFD calculations. Downstream the differential pumping the particle beam is used to continuously refill a linear ion trap. For the trapping of particles in the size range of several kDa to MDa, a radio frequency from 10-150 kHz is. In contrast to the work of other groups, which are using digital ion traps, we developed an amplifier capable to provide an appropriate sinusoidal voltage with amplitude up to 3kV. This assembly is capable to inject nanoparticles into vacuum chambers in a highly efficient way. The dilution of the particle number concentration arising from the gas expansion from room pressure into vacuum is compensated by concentrating the particles in a small cylindrical volume by electrodynamic trapping. The enlargement of the target density compared to a free molecular beam provides a tool for various techniques of spectroscopy used on smaller ions by routine.
    04/2009;
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    ABSTRACT: Cavity enhanced methods in absorption spectroscopy have seen a considerable increase in popularity during the past decade. Especially Cavity Enhanced Absorption Spectroscopy (CEAS) established itself in atmospheric trace gas detection by providing tens of kilometers of effective light path length using a cavity as short as 1 m. In our poster we present a compact and power efficient light emitting diode based broadband Cavity Enhanced Differential Optical Absorption Spectrometer (CE-DOAS) for in situ field observation of atmospheric NO3. This device combines the small size of the cavity with the enormous advantages of the DOAS approach in terms of sensitivity and specificity. In particular, no selective removal of the analyte (here NO3) is necessary. The instrument was compared to other trace gas detection techniques in an intercomparison campaign in the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich at NO3 concentrations as low as 6.3 ppt.
    04/2009;
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    ABSTRACT: Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. Initial approaches made use of monochromatic cavity ring-down (CRD) devices, while more recently steady state approaches became known as cavity enhanced absorption spectroscopy (CEAS) technologies. An interesting approach is the combination of CEAS with broad band light sources. Broad-band CEAS (BB-CEAS) has several enormous advantages over CRD. For instance LED's can be used instead of pulsed lasers, significant simplifying the instrumental set-up. Furthermore, BB-CEAS absorption spectra can be analysed using the DOAS technique realising all advantages of DOAS. This cavity enhanced DOAS (CE-DOAS) technique offers e.g. sensitive detection of very small differential absorption structures (usually vibrational molecular bands), quantitative detection of a particular molecule, simultaneous measurement of several molecular species with overlapping spectra and even determination of the aerosol extinction. In contrast to the CRD technique, where the shortening (compared to the "empty" cavity) of the ring-down time is always proportional to the additional absorbance, an important problem associated with BB-CEAS is the reduction of the light path by the trace gas absorption. In extreme, but not unrealistic cases the optical density of an absorption structure can become nearly independent of the trace gas concentration in the cavity, thus the CEAS Method would almost completely loose its sensitivity to trace gas absorptions. In typical applications the optimum sensitivity is reached in situations where the light path reduction effect is neither negligible nor dominating, thus correction of this effect is required. We present a detailed, theoretical investigation of these relationships, present several methods to correct for the cases between the two above extremes, and demonstrate the usefulness of our new approach with experimental data.
    03/2009; 11:6367.
  • European Aerosol ConferenceEuropean Aerosol Conference; 01/2009
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    ABSTRACT: Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broad band light sources, the broad-band CEAS (BB-CEAS). BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality ( Q ) of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (esp. at very high mirror reflectivity), the light path will vary inversely with the trace gas concentration and the strength of the band will become nearly independent of the trace gas concentration c in the cavity, rendering the CEAS Method useless for trace gas measurements. Only in the limiting case where the mirror reflectivity determines Q at all wavelength, the strength of the band as seen by the BB-CEAS instrument becomes proportional to the concentration c . We investigate these relationships in detail and present methods to correct for the cases between the two above extremes, which are of course the important ones in practice.
    Atmospheric Measurement Techniques Discussions. 01/2008;
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    ABSTRACT: Cavity enhanced methods in absorption spectroscopy have seen a considerable increase in popularity during the past decade. Especially Cavity Enhanced Absorption Spectroscopy (CEAS) established itself in atmospheric trace gas detection by providing tens of kilometers of effective light path length using a cavity as short as 1 m. In this paper we report on the construction and testing of a compact and power efficient light emitting diode based broadband Cavity Enhanced Differential Optical Absorption Spectrometer (CE-DOAS) for in situ field observation of atmospheric NO3. This device combines the small size of the cavity with the enormous advantages of the DOAS approach in terms of sensitivity and specificity. In particular, no selective removal of the analyte (here NO3) is necessary, thus the CE-DOAS technique can – in principle – measure any gas detectable by DOAS. We will discuss the advantages of using a light emitting diode (LED) as light source particularly the precautions which have to be satisfied for the use of LEDs. The instrument was tested in the lab by detecting NO3 in a mixture of NO2 and O3 in air. It was then compared to other trace gas detection techniques in an intercomparison campaign in the atmosphere simulation chamber SAPHIR at NO3 concentrations as low as 6.3 ppt.
    Atmospheric Chemistry and Physics 01/2008; · 4.88 Impact Factor
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Publication Stats

43 Citations
27.59 Total Impact Points

Institutions

  • 2010–2012
    • Karlsruhe Institute of Technology
      • Institute of Meteorology and Climate Research
      Carlsruhe, Baden-Württemberg, Germany
  • 2009–2010
    • Universität Heidelberg
      • Institute of Environmental Physics
      Heidelberg, Baden-Wuerttemberg, Germany
    • Klinikum Karlsruhe
      Carlsruhe, Baden-Württemberg, Germany