Narrow Results

It is demonstrated in this work, that PIXE is a good mass indicator for suspended particles in urban environments. Results are presented for several samplings performed in urban and other environments in Chile and other countries. Aerosols were collected on filters operated by a Stacked Filter Unit (SFU) in the range of particles < 15 µm (PM₁₅) and < 10 µm (PM₁₀), mainly the respirable fraction. For samplings performed in downtown Santiago, the sum of the concentrations of the elements detected by PIXE correlated well with the indices of respirable suspended particles (RSP) measured by gravimetry. There was no high correlation for other samplings, near a crushing plant and near mineral storage. On the average, the sum of the PIXE results for Santiago’s aerosols represents about the 15% of the total mass collected in the respirable fraction. A measurement of collection efficiency for the 0.4 µm Nuclepore filter was performed by means of PIXE and gravimetry. These results were η_PIXE=0.98 and η_balance=0.96, for the PIXE and the gravimetric method.

Nuclepore filters have been widely used for collecting atmospheric aerosols and such samples are quite convenient for PIXE since they can be analyzed without any treatment. However, some special methods, (which is somewhat different from existing standard methods for general samples), must be applied in order to perform quantitative analysis. We have developed a method of quantitative analysis for all elements making use of bromine, which is almost uniformly contained in general Nuclepore filters, as an internal standard. Then, for quantitative analysis of light elements, the standard-free method, which makes use of total yield of continuous x-rays, has been applied and it is found that this method can be successfully applied to practical aerosol samples. Moreover, the method was applied to bio-samples prepared by cutting frozen samples with a microtome, and the result is almost satisfactory. It is found that the present method can be successfully applied to any sample which can be made uniform.