Mössbauer Spectroscopy and Scanning Electron Microscopy Studies of Road Dust Sediments in Urban Environment of Sofia – The Bulgaria’s Capital City

The annual and daily maximum permissible values applicable to the concentrations of fine particles with diameter up to ten micrometers (Particles Micrometers 10, PM10) in the city of Sofia as well as in several other Bulgarian cities and regions have been found to exceed the limit values more than 2.5 times for 90 days per year. Air quality is one of the main factors determining the quality of life. According to the European Commission, air pollution is still the most serious environmental and health problem in the EU, with annual deaths estimated at around 400 000 people. Two methods have been chosen for the study of road dust deposits containing fine iron-containing particles in the city of Sofia: Mössbauer spectroscopy and scanning electron microscopy with the possibility of X-ray fluorescence analysis and determination of the chemical elemental composition of the objects, as well as their size and shape. The Mössbauer spectroscopy studies at liquid nitrogen temperature allow making at least semi-quantitative estimates of the content of ultrafine iron-containing particles with superparamagnetic properties. Iron is included mostly in the form of oxides and hydroxides. The presence of a large amount of fine dust particles of metallic iron, α-Fe, is clear evidence of a significant technogenic contribution to the pollution of Sofia’s air. The finest dust component with concentrations between 10 and 20% is in a superparamagnetic state and is observed as fine incrustations on the surface of silicates. In places with intense traffic and large-scale construction activities, an increased concentration of man-made dust sediments is noticed.