The four-wavelength Photoacoustic Aerosol Absorption Spectrometer (PAAS-4 λ )

• Main Authors: Schnaiter, Franz Martin, Linke, Claudia, Asmi, Eija, Servomaa, Henri, Hyvärinen, Antti-Pekka, Ohata, Sho, Kondo, Yutaka, Järvinen, Emma
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: ddc:550; Earth sciences; info:eu-repo/classification/ddc/550; Arctic
• Online Access: https://publikationen.bibliothek.kit.edu/1000160687; https://publikationen.bibliothek.kit.edu/1000160687/151027898; https://doi.org/10.5445/IR/1000160687

In this paper, the Photoacoustic Aerosol Absorption Spectrometer (PAAS-4λ) is introduced. PAAS-4λ was specifically developed for long-term monitoring tasks in (unattended) air quality stations. It uses four wavelengths coupled to a single acoustic resonator in a compact and robust set-up. The instrument has been thoroughly characterized and carefully calibrated in the laboratory using NO$_2$/air mixtures and Nigrosin aerosol. It has an ultimate 1σ detection limit below 0.1 Mm$^{−1}$, at a measurement precision and accuracy of 3 % and 10 %, respectively. In order to demonstrate the PAAS-4λ suitability for long-term monitoring tasks, the instrument is currently validated at the air quality monitoring station Pallas in Finland, about 140 km north of the Arctic circle. A total of 11 months of PAAS-4λ data from this deployment are presented and discussed in terms of instrument performance. Intercomparisons with the filter-based photometers of a continuous soot monitoring system (COSMOS), the Multi-Angle Absorption Photometer (MAAP), and Aethalometer (AE33) demonstrate the capabilities and value of PAAS-4λ, as well as for the validation of the widely used filter-based instruments.