Articles | Volume 9, issue 11
Atmos. Meas. Tech., 9, 5331–5346, 2016
Atmos. Meas. Tech., 9, 5331–5346, 2016

Research article 07 Nov 2016

Research article | 07 Nov 2016

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

Claudia Linke1, Inas Ibrahim1, Nina Schleicher2, Regina Hitzenberger3, Meinrat O. Andreae4, Thomas Leisner1, and Martin Schnaiter1 Claudia Linke et al.
  • 1Institute of Meteorology and Climate Research, Atmospheric Aerosol Research, KIT, Karlsruhe, Germany
  • 2Institute of Geography and Geoecology, KIT, Karlsruhe, Germany
  • 3University of Vienna, Faculty of Physics, Vienna, Austria
  • 4Biogeochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. The spectral light-absorbing behavior of carbonaceous aerosols varies depending on the chemical composition and structure of the particles. A new single-cavity three-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 section (MAC) values, 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 increase, 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.

Short summary
Various carbonaceous materials are present in the atmosphere. Besides gaseous organic compounds, carbonaceous particles like soot are emitted into the air from traffic sources, residential wood combustion, or wildfires. Variable chemical compositions of such materials, which often result from incomplete combustion processes, show differences in the absorption behavior at visible wavelengths. Our instrument is able to measure the absorption at three visible wavelengths.