The use of computer controlled scanning electron microscopy in environmental studies

Abstract

The microscope has long been used to identify the chemical and morphological characteristics of features too small to be detected with the naked eye. The ability to analyze individual microscopic features provides a resolution of sample constituents and their associations unobtainable by most gross or bulk analysis methods. Because of this increased resolution, both light (optical) and electron microscopy have often been employed in the analysis of particulate matter. However, manual microscopic analysis is both tedious and time consuming. Therefore, the results obtained from manual microscopic analysis have usually been only qualitative because of the relatively small number of particles characterized. A quantitative analysis requires reproducible sizing and identification of individual particles in numbers sufficient to satisfy statistical counting requirements. Using automated imaging, computer controlled scanning electron microscopy (CCSEM) can provide quantitative results within a reasonable analysis time. Because of this automation, microscopy has entered a new era. CCSEM permits comparison of microscopic results with those from bulk analyses while retaining the feature specific resolution of manual microscopy. The replicability, precision, and accuracy of CCSEM were recently evaluated during a study for the Texas Air Control Board. Elemental concentrations obtained by CCSEM were compared with those from several bulk analysis methods. The CCSEM results were determined to be quantitative. The environmental applications of CCSEM described in this paper are: a determination of equivalent aerodynamic diameters, b air particulate sampler inlet modeling, c source emission characterization, and d receptor modeling. © 1983 Air & Waste Management Association.