A NOVEL SINGLE - CAVITY MULTI - WAVELENGTH PHOTOACOUSTIC SPECTR OMETER FOR ATMOSPHERIC AEROSOL RESEARCH

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 pho toacoustic spectrometer was developed and characterized for measuring absorption coefficients at three wavelengths across the visible spectral range. In laboratory 15 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 A ngstrom exponents ( α abs and α sca ), 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 20 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 aero sol. Depending on the OC content, the Angstrom 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 25 site a daily average value of α abs (445 - 660) of 1.9 was found .