Science & Technologies Volume V, Number 2, 2015 Nautical & Environmental studies 1 EXPERIMENTAL STUDY ON ELEMENTAL COMPOSITION OF PM 10 IN SOFIA, 2012-2014 Blagorodka Veleva * , Elena Hristova * , Emilia Nikolova ** , Maria Kolarova * , Raliza Valcheva ** * National Institute of Meteorology and Hydrology, NIMH-BAS, Tsarigradsko sh. 66, Sofia ** Institute of Nuclear Research and Nuclear Energy, INRNE-BAS, Tsarigradsko sh. 72, Sofia Corresponding author e-mail: Elena.Hristova@meteo.bg ABSTRACT Particulate matter, PM 10 and PM 2.5 is a serious problem for the urban air pollution in many Bulgarian cities. PM 10 harmful health effect is well known and depends on the concentration, size and chemical composition. The present study is focused on the elemental composition of PM 10 applying ED-XRF technique. Six experimental campaigns were organized at the NIMH, Sofia in winter and summer periods of 2012, 2013 and 2014. The results of PM 10 mass concentration and the elemental composition of more than 20 elements (P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn Br, Rb, Sr, Y, Zr, Cd, Sn, Sb, I, Ba, Pb) have shown that there are significant variations in maximum and mean concentrations. The concentrations of PM 10 and most components are lower in the summer periods. The maximum and average concentrations of Ca tended to increase from 2012 to 2014. The mean concentrations of S, K, Fe, Ti, Cu and Zn measured during the winter and summer periods of 2013 are lower than those in 2012 and 2014. Basic statistical parameters obtained for the entire data set are summarized for the winter and summer periods. Keywords: urban air pollution, PM 10 , elemental composition, X-ray fluorescence analysis, ED- XRF. Introduction The city of Sofia has the highest health risk of air pollution in comparison with other Bulgarian cities, because of the topography of the closed valley Sofiisko pole surrounded by mountains, and the presence of different industrial, traffic and domestic pollutant sources which could affect the most populated area in the country. The toxicity of particulate matter (PM) depends not only on the size but to a significant extent on the chemical composition of the aerosol particles. Therefore it is an important task to characterize the chemical composition of the particulate matter, including macro and micro elements. PM is a mixture of aerosol particles (solid and liquid) covering a wide range of sizes and chemical compositions. PM 10 (PM 2.5 ) refers to particles with a diameter of 10 (2.5) micrometers or less. Particulate matter is either directly emitted as primary particles or is formed from SO 2 , NO x , NH 3 , NMVOCs gasses as secondary aerosol. PM is emitted from many anthropogenic sources, including both combustion and non-combustion sources. Important natural sources of PM are sea salt and natural re-suspended dust (Air pollution fact sheet 2014, Bulgaria, EEA). Crustal elements like Si, Al, Fe, Ca and partly K could be mainly attributed to airborne soil and road dust. Vehicle traffic is a potential source of cadmium, lead, manganese, and nickel as a result of fuel combustion and the wearing of brakes, tires, and other components (Johansson et. al., 2009; Gao et al., 2015). Arsenic, cadmium, chromium, lead, nickel and other trace elements could be emitted from coal-burning and metal-processing facilities. Experimental Sampling and mass concentration measurements PM 10 sampling was carried out with a certified sampler at the site of NIMH Central Meteorological Observatory (CMO) in Sofia during the field campaigns: 6–25.02.2012; 2- 26.07.2012; 21.01-11.02.2013; 1-21.07.2013; 6.02-26.02.2014 and 21.07-13.08.2014. The CMO of