Auflistung nach Autor:in "Visser, Bradley"

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  • Vorschaubild
    Publikation
    A dual-wavelength photothermal aerosol absorption monitor. Design, calibration and performance
    (Copernicus, 2022) Drinovec, Luka; Jagodič, Uroš; Pirker, Luka; Škarabot, Miha; Kurtjak, Mario; Vidović, Kristijan; Ferrero, Luca; Visser, Bradley; Röhrbein, Jannis; Weingartner, Ernest; Kalbermatter, Daniel M.; Vasilatou, Konstantina; Bühlmann, Tobias; Pascale, Celine; Müller, Thomas; Wiedensohler, Alfred; Močnik, Griša [in: Atmospheric Measurement Techniques]
    There exists a lack of aerosol absorption measurement techniques with low uncertainties and without artefacts. We have developed the two-wavelength Photothermal Aerosol Absorption Monitor (PTAAM-2λ), which measures the aerosol absorption coefficient at 532 and 1064 nm. Here we describe its design, calibration and mode of operation and evaluate its applicability, limits and uncertainties. The 532 nm channel was calibrated with ∼ 1 µmol mol−1 NO2, whereas the 1064 nm channel was calibrated using measured size distribution spectra of nigrosin particles and a Mie calculation. Since the aerosolized nigrosin used for calibration was dry, we determined the imaginary part of the refractive index of nigrosin from the absorbance measurements on solid thin film samples. The obtained refractive index differed considerably from the one determined using aqueous nigrosin solution. PTAAM-2λ has no scattering artefact and features very low uncertainties: 4 % and 6 % for the absorption coefficient at 532 and 1064 nm, respectively, and 9 % for the absorption Ångström exponent. The artefact-free nature of the measurement method allowed us to investigate the artefacts of filter photometers. Both the Aethalometer AE33 and CLAP suffer from cross sensitivity to scattering – this scattering artefact is most pronounced for particles smaller than 70 nm. We observed a strong dependence of the filter multiple scattering parameter on the particle size in the 100–500 nm range. The results from the winter ambient campaign in Ljubljana showed similar multiple scattering parameter values for ambient aerosols and laboratory experiments. The spectral dependence of this parameter resulted in AE33 reporting the absorption Ångström exponent for different soot samples with values biased 0.23–0.35 higher than the PTAAM-2λ measurement. Photothermal interferometry is a promising method for reference aerosol absorption measurements.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    A single-beam photothermal interferometer for in situ measurements of aerosol light absorption
    (Copernicus, 2020) Visser, Bradley; Röhrbein, Jannis; Steigmeier, Peter; Drinovec, Luka; Močnik, Griša; Weingartner, Ernest [in: Atmospheric Measurement Techniques]
    We have developed a novel single-beam photothermal interferometer and present here its application for the measurement of aerosol light absorption. The use of only a single laser beam allows for a compact optical set-up and significantly easier alignment compared to standard dual-beam photothermal interferometers, making it ideal for field measurements. Due to a unique configuration of the reference interferometer arm, light absorption by aerosols can be determined directly – even in the presence of light-absorbing gases. The instrument can be calibrated directly with light-absorbing gases, such as NO2, and can be used to calibrate other light absorption instruments. The detection limits (1σ) for absorption for 10 and 60 s averaging times were determined to be 14.6 and 7.4 Mm−1, respectively, which for a mass absorption cross section of 10 m2 g−1 leads to equivalent black carbon concentration detection limits of 1460 and 740 ng m−3, respectively. The detection limit could be reduced further by improvements to the isolation of the instrument and the signal detection and processing schemes employed.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Comparing black carbon and aerosol absorption measuring instruments – a new system using lab-generated soot coated with controlled amounts of secondary organic matter
    (Copernicus, 2022) Kalbermatter, Daniel M.; Močnik, Griša; Drinovec, Luka; Visser, Bradley; Röhrbein, Jannis; Oscity, Matthias; Weingartner, Ernest; Hyvärinen, Antti-Pekka; Vasilatou, Konstantina [in: Atmospheric Measurement Techniques]
    We report on an inter-comparison of black-carbon- and aerosol-absorption-measuring instruments with laboratory-generated soot particles coated with controlled amounts of secondary organic matter (SOM). The aerosol generation setup consisted of a miniCAST 5201 Type BC burner for the generation of soot particles and a new automated oxidation flow reactor based on the micro smog chamber (MSC) for the generation of SOM from the ozonolysis of α-pinene. A series of test aerosols was generated with elemental to total carbon (EC / TC) mass fraction ranging from about 90 % down to 10 % and single-scattering albedo (SSA at 637 nm) from almost 0 to about 0.7. A dual-spot Aethalometer AE33, a photoacoustic extinctiometer (PAX, 870 nm), a multi-angle absorption photometer (MAAP), a prototype photoacoustic instrument, and two prototype photo-thermal interferometers (PTAAM-2λ and MSPTI) were exposed to the test aerosols in parallel. Significant deviations in the response of the instruments were observed depending on the amount of secondary organic coating. We believe that the setup and methodology described in this study can easily be standardised and provide a straightforward and reproducible procedure for the inter-comparison and characterisation of both filter-based and in situ black-carbon-measuring (BC-measuring) instruments based on realistic test aerosols.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Single aerosol particle detection by acoustic impaction
    (IEEE, 2022) Karlen, Nadine; Rüggeberg, Tobias; Visser, Bradley; Hoffmann, Jana; Weiss, Daniel; Weingartner, Ernest [in: IEEE Sensors Journal]
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Vorschaubild
    Publikation
    Waveguide based passively demodulated photothermal interferometer for light absorption measurements of trace substances
    (Optica Publishing Group, 2023) Visser, Bradley; Bilal, Jonas; Flöry, Nikolaus; Wipf, Manuela; Steigmeier, Peter; Rüggeberg, Tobias; Betschon, Felix; Weingartner, Ernest [in: Applied Optics]
    01A - Beitrag in wissenschaftlicher Zeitschrift