Usage of Scanning Electron Microscopy for Particulate Matter Sources Identification

Abstract

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 have except typical chemical composition also the specific shape reflecting the way of formation, so it is possible to conclude the source. Scanning electron microscope VEGA TS 5136 LSU (Tescan, s.r.o., Czech Republic) was used for PM imaging. PM air samples were captured on the special filters Millipore made of polycarbonate membrane (Isopore) with the 0.6 µm size of pores. PM samples were taken both near the exhaust of gasoline and diesel engine to define PM shapes emitted from combustion processes in vehicles and also on 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 broom and by vacuum cleaner to identify PM generated by resuspension. Separate spherical particles were observed on filter exposed near gasoline vehicle exhaust pipe and their aggregates near diesel vehicle exhaust. Spherical particles aggregates were also observed on filters exposed on locality with high traffic intensity where road traffic is considered to be the dominant source of air pollution. Larger spherical particles that represent products of coal combustion were found on locality near industrial area. The other particle shapes except the spherical particles were often observed on the localities that represent more opened 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 that evidence significant contribution of other processes to overall PM air pollution namely resuspension.