A novel single-cavity multi-wavelength photoacoustic spectrometer for atmospheric aerosol research

Abstract

Abstract. The spectral light absorbing behavior of carbonaceous aerosols varies depending on the chemical composition and structure of the particles. A new single-cavity multi-wavelength photoacoustic spectrometer was developed and characterized for measuring absorption coefficients at three wavelengths across the visible spectral range. In laboratory studies, several types of soot with different organic content were generated by a diffusion flame burner and were investigated for changes in mass-specific absorption cross sections (MAC), absorption and scattering Ångström exponents (αabs and αsca), and single scattering albedo (ω). By increasing the organic carbonaceous (OC) content of the aerosol from 50 % to 90 % of the total carbonaceous mass, for 660 nm nearly no change of MAC was found with increasing OC content. In contrast, for 532 nm a significant, and for 445 nm a strong increase of MAC was found with increasing OC content of the aerosol. Depending on the OC content, the Ångström exponents of absorption and scattering as well as the single scattering albedo increased. These laboratory results were compared to a field study at a traffic dominated urban site, which was also influenced by residential wood combustion. For this site a daily average value of αabs(445–660) of 1.9 was found.

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

“…Recently, this artefact was studied for single micrometer-sized particles of tetraethylene glycol and a significant size dependence of the magnitude and sign of the artefact was observed (Diveky et al, 2019). Some photoacoustic instruments can achieve detection limits of ≈ 0.1 Mm -1 (with 60 s averaging) (Lack et al, 2006), though most instruments have considerably higher 85 detection limits (Linke et al, 2016).…”