A single-beam photothermal interferometer for in situ measurements of aerosol light absorption

• Published in: Atmospheric measurement techniques Vol. 13; no. 12; pp. 7097 - 7111
• Main Authors: Visser, Bradley, Röhrbein, Jannis, Steigmeier, Peter, Drinovec, Luka, Mocnik, GriÅ¡a, Weingartner, Ernest
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 23.12.2020; Copernicus Publications
• Subjects: Absorption; Absorption cross sections; Aerosol absorption; Aerosol light absorption; Aerosols; Air pollution; Black carbon; Calibration; Carbon; Carbon content; Comparative analysis; Detection; Detection limits; Electromagnetic absorption; Endangered & extinct species; Extinction; Gases; In situ measurement; Information processing; Instruments; Interferometry; Laser beams; Lasers; Light; Light absorption; Measurement; Measurement techniques; Nitrogen dioxide; Noise; Optical instruments; Outdoor air quality; Signal detection; Signal processing
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-13-7097-2020

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.