Electron microscopic evaluation of atmospheric dust.

For the determination of the health hazards to humans of inhaled dust particles, precise collection and evaluation techniques are needed. The sampling system has to be designed in order to obtain representative samples and has also to take into consideration the type of electron microscopy evaluation which will be applied. A convenient method is the collection of dust particles on conventional membrane filters (MF) or on Nuclepore polycarbonate filters (NPF); their characteristics are outlined. The preparation of filters is a decisive procedure, both for SEM (low magnification) and for TEM evaluation. The advantages and disadvantages of the two electron microscopic techniques are described and discussed. As an example of practical application, the results of ambient air fiber measurements in the cities of Düsseldorf and Duisburg, and in an urban site 50 km away from the nearest city for the period 1981-83 are reported. From these results, it seems possible to obtain useful and realistic informations on particulate air pollutants when using both electron microscopy techniques.