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Particulate matter (PM) diameter and shape are the most discussed physical properties considering behaviour characterisation, source identification, and possible effects on human health. Some groups of particles not only have a typical chemical composition but also a specific shape reflecting the method of their formation, so it is possible to deduce the source. A scanning electron microscope VEGA TS 5136 LSU (Tescan, s.r.o., Czech Republic) was used for PM imaging. PM air samples were captured on Millipore special filters made of polycarbonate membrane (Isopore) with a 0.6 µm size of pores. PM samples were taken both from near the exhaust of gasoline and diesel engines to define PM shapes emitted from combustion processes in vehicles, and also from chosen localities that represent urban sites with different traffic intensity and with different possible PM sources (transportation, industry). Samples of street dust were also collected by sweeping with a broom and with a vacuum cleaner to identify PM generated by resuspension. Separate spherical particles were observed on exposed filters near a gasoline vehicle's exhaust pipe and their aggregates near a diesel vehicle's exhaust. Spherical particles aggregates were also observed on filters exposed at a locality with a high traffic intensity where road traffic is considered to be the dominant source of air pollution. Larger spherical particles that represent the products of coal combustion were found at a locality near an industrial area. Other particle shapes, excluding spherical particles, were often observed at the localities that represent a more open area with more trees. Sharp-edged particles of geological origin (soils) and larger spherical or elongated particles of biological origin (spores) were also often observed on the filters from these localities which is evidence of a significant contribution of other processes to the overall PM air pollution, namely resuspension.

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