Measurement of fine particulate matter using electron microscopy techniques

Ambient fine particulate matter, defined as material with an aerodynamic diameter less than or equal to 2.5 mum (PM2.5), comprises a broad range of primary and secondary particles that are dispersed through the atmosphere from a variety of sources. Attention has recently shifted to investigating ambient PM2.5 because fine particles are thought to have a greater influence on health effects. Of particular interest are sources of fossil fuel combustion because they have been hypothesized as potentially contributing to the observed link between atmospheric particulate matter and health effects. Current studies are focused on the use of multiple analytical techniques to assist in the characterization of particulate matter to gain a better understanding of the relationship between anthropogenic emission sources and ambient PM2.5. Electron microscopy techniques are being employed to provide information on the size, morphology, and elemental composition of individual particles. Individual particle data offers the potential to more specifically identify and quantify sources of particulate matter contributing to ambient air quality. However, electron microscopy has not been widely utilized in air quality studies because of the difficulties associated with collecting a sample that is well suited for individual particle analysis. Recent improvements in sampling technology, specifically the speciation sampler, permit collection of samples that are more amenable for electron microscopy analysis. This paper discusses the application of electron microscopy in environmental studies for individual particle analysis using scanning electron microscopy (SEM), computer-controlled scanning electron microscopy (CCSEM), and transmission electron microscopy (TEM) techniques. The paper also addresses managing the difficulties associated with the characterization of fine particulate matter using electron microscopy due to substrate interference and describes the benefits of sample collection with speciation samplers. (C) 2004 Published by Elsevier B.V