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A single-beam photothermal interferometer for in situ measurements of aerosol light absorption
Bradley Visser, Jannis Röhrbein, Peter Steigmeier, Luka Drinovec, Griša Močnik, Ernest Weingartner, 2020, original scientific article

Abstract: 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.
Found in: osebi
Keywords: aerosol, aerosol absorption, black carbon, photo-thermal interferometer, climate change
Published: 29.12.2020; Views: 1311; Downloads: 36
.pdf Fulltext (2,44 MB)

Comparing black-carbon- and aerosol-absorption-measuring instruments – a new system using lab-generated soot coated with controlled amounts of secondary organic matter
Antti-Pekka Hyvärinen, Konstantina Vasilatou, Matthias Oscity, Ernest Weingartner, Bradley Visser, Jannis Röhrbein, Luka Drinovec, Daniel M. Kalbermatter, Griša Močnik, 2022, original scientific article

Abstract: 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.
Found in: osebi
Keywords: black carbon, aerosol absorption, secondary organic aerosol, coating
Published: 01.02.2022; Views: 309; Downloads: 7
.pdf Fulltext (752,94 KB)

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