Characterization of fine mode atmospheric aerosols by Raman microscopy and diffuse reflectance FTIR.

A combination of Raman microscopy and diffuse reflectance Fourier transform infrared spectroscopy (FTIR) has been used for the characterization of fine mode (<1 μm) tropospheric aerosols. Peak fitting was used to identify five overlapping bands in the Raman spectra. These bands have been identified as due to combustion generated carbon soot as well as large molecular organic carbon species. The fwhm of the D band at 1400 cm(-1) as well as the ratio of intensities of the D3 band at 1550 cm(-1) to the G band at 1580 cm(-1) can serve as a measure of the aerosol organic carbon content. Raman microscopy combined with spectral mapping capabilities was used to investigate the composition of the fine mode aerosols at the particle level, allowing for the direct determination of aerosol mixing state. Results showed that the fine aerosols were predominately internally mixed particles composed of carbon soot coated with molecular organic carbon species. Characterization of the aerosols by diffuse reflectance FTIR showed that the major organic carbon species were polycarboxylates and polysaccharide-like species typical of humic-like substances (HULIS).