Preliminary evaluation of micro-Raman spectrometry for the characterization of individual aerosol particles.

Raman spectrometry has been used to determine the graphitic C content and to estimate particle size and disordered character of the C in aerosol particulate matter collected on filters, with sample spot sizes on the order of 100 microm being analyzed. Individual analysis of particulate matter with aerodynamic diameters less than 10 microm has therefore not been considered. In this investigation, various size fractions of aerosol particulate matter originating from both indoor and outdoor sources were collected by means of impactors or passive dry deposition on different types of substrate and analyzed by means of micro-Raman spectrometry with spot sizes ranging from 1-5 microm. The aim was to investigate the possible application of micro-Raman spectrometry to the molecular characterization of individual aerosol particles and to assess the applicability of the various substrates in such an analysis. It was demonstrated that the molecular characterization of most inorganic particles is trivial, but organic and heterogeneous conglomerates proved to be more challenging. Spectral contributions of the substrates, currently favored for individual particle analysis, were significant. Results obtained from micro Raman spectrometry can certainly add valuable molecular information on individual aerosol particles as small as 1 microm aerodynamic diameter.