A new sample preparation protocol for SEM and TEM particulate matter analysis

Highlights: • A new sample preparation methodology was developed for SEM and TEM analysis of PM. • The methodology favoured efficient transfer of PM from sampling substrates onto acetate film. • Through this methodology, SEM specimens could retain their original spatial distribution. • TEM specimens composed of sub-micron particles could also yield crystallographic information. • The methodology could be used even when collected particles were extremely limited in the amount. A new methodology has been developed to prepare electron microscopy, both SEM and TEM, specimens starting from particulate matter collected using environmental sampling systems. The approach is based on the extraction of the particles to be analyzed from the harvesting substrates. The extracted particles can be directly observed in an SEM, possibly in low-vacuum mode to prevent electrical charging. In order to prepare electron transparent samples, TEM observations require a further step, consisting in embedding the particles in an electron transparent carbon film deposited before dissolving the acetate extracting substrate. The protocol has been tested by analyzing particles collected during bench tests on brake pads and discs, carried out on a dynamometer equipped with a particulate matter sampling apparatus. The main advantages of the approach are: the complete extraction of the particulate matter specimens from the original substrates, that in this way do not interfere with the analyses; the extracted samples retain the topological information of the collection in the specimens prepared for SEM; possibility to be applied to any kind of particulate matter harvesting substrates.