Combining Raman Chemical Imaging and Scanning Electron Microscopy to Characterize Ambient Fine Particulate Matter

Raman chemical imaging and scanning electron microscopy (Raman/SEM) have been used in a preliminary study to determine the size, morphology, elemental and molecular composition, and molecular structure of fine particulate matter in several test samples and one ambient air sample. Raman chemical imaging and SEM, respectively, provide a way to spatially characterize a sample based on its molecular and elemental makeup. When combined, Raman chemical imaging and SEM provide detailed spatial, elemental, and molecular information for particulate matter as small as 250 nm. Initial studies demonstrate the potential of Raman/SEM for molecular and elemental determination of organic and inorganic fine particulate matter. This has been accomplished by analyzing samples with fine particulate matter using each method independently. Since both techniques are nondestructive, particles of interest can be relocated between instruments. Practical issues such as filter substrate compatibility and instrumentation compatibility are addressed. In addition, first results showing Raman/SEM chemical images from several standard materials, as well as ambient PM_2.5 samples, are reported.