Chemical composition of atmospheric aerosol particles

Effects of the atmospheric aerosol depend not only on the concentration and size but also on the chemical composition of particles. For this reason the study of the chemical nature of particulate matter in the atmosphere is of crucial importance. This study is rather complicated because of the small mass and concentration of the particles. Furthermore, due to coagulation, condensation and gas adsorption processes, one particle can contain several different materials, that is, the aerosol is internally mixed9. 

9 By contrast, an external mixture contains particles, each of which is composed of a pure substance. 

Modern bulk analysis methods make possible non-destructive chemical identification, which means that the sample remains intact after the analysis. Such a procedure is provided by electron microprobe or X-ray fluorescence analyses, in which the sample is irradiated by electron beams or X-rays and the elemental composition is determined on the basis of induced characteristic X-ray emissions. These methods have been successfully employed to study both stratospheric (Junge, 1963) and tropospheric (Gillette and Blifford, 1971) aerosol particles. Neutron activation analysis is also widely used to identify the chemical composition of atmospheric particulate matter (e.g. Duceef ai, 1966 Rahn etal., 1971) this is also a non-destructive procedure. 

The third major class of analytical techniques may be called morphological methods. This identification consists of comparing the form of particles captured with the morphology of particles of known composition. It goes without saying that morphological similarity is a necessary but not always sufficient condition for compositional identity. In spite of this problem this procedure is widely employed mainly in clean atmosphere, since even Aitken size particles can be identified morphologically (A. Meszaros and Vissy, 1974 Butor, 1976). 

In the fourth type of identification the chemical composition of particles is studied in situ. By suitable chemical aerosol instruments the concentration and the size distribution of certain elements can be continuously monitored. The flame photometry of sodium containing particles (e.g. Hobbs, 1971) is a good example for such a method. Recently flame photometric detectors have also been developed to measure aerosol sulfur in the atmosphere (e.g. Kittelson et at., 1978). 

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Chemical composition of atmospheric aerosol particles expressed in percentage of the number of particles with radius larger than 0.03 pm (A. Meszaros and Vissy, 1974)... 

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