Raman scattering and the characterisation of atmospheric aerosol particles

Abstract

AIRBORNE particulates have a major role in the air pollution problem. They are responsible for acid rain, reduced visibility, and, in certain size ranges, are deposited in the lungs where they can cause various disorders. Considerable effort has been expended in the analysis of these particulates using techniques such as wet chemistry, X-ray fluorescence, infrared spectroscopy and ESCA. Yet there are still great uncertainties as to the chemical form and origin of many of the particulate species. We describe here preliminary studies of the feasibility of characterising particulate pollutants by means of Raman spectroscopy. We believe that this is the first attempt to apply this spectroscopic technique in this area of research. The samples studied included diesel exhaust particles, automobile exhaust particles (unleaded fuel, no catalytic converter) and several ambient air samples. The spectra from these samples were compared with those of polycrystalline graphite and activated carbon which were used as references. Our results indicate that physical structures similar to activated carbon are at least a major species and may be the dominant species in both source-enriched and ambient samples. The implications of this observation could be quite important in terms of atmospheric chemistry, health effects, weather modifications and the effects of aerosols on the albedo.