Airborne lead-210 is a useful tracer for studying air mass origin and transport. ²¹⁰Pb is produced in the atmosphere by the decay of the radioactive noble gas ²²²Rn, emanating after ²²⁶Ra decay from the earth crust. The results obtained for ²¹⁰Pb concentration in total suspended particulate (TSP) display seasonal pattern with maximum in the summer-autumn period. The TSP filters are collected within the scope of atmospheric radioactivity monitoring in NIMH, Bulgaria and were measured initially for short and long lived beta radionuclides. The methodology developed in FMI, Finland, based on gross alpha counting of ²¹⁰Po- the daughter of the combined aerosol filters samples collected in Sofia during the period 2001 – 2003 and 2006-2007, is applied. The first results for ²¹⁰Pb in particulate matter, fraction below 10 μm (PM₁₀), in February 2012 in Sofia are presented. The alpha counting methodology was successfully applied for daily PM10 quartz filters with the counting uncertainty value of ≤20%. Lead-210 daily concentration is compared to the PM₁₀ mass concentration and elemental lead concentration, determined by EDXRF technique. The comparison between ²¹⁰Pb, elemental lead and PM₁₀ mass concentration reveals a different time variation for days with cyclonic weather and mass transport from south-west and an anticyclone episode with increasing PM₁₀, lead-210 and lead concentrations from day to day. An increase in the PM₁₀/²¹⁰Pb ratio indicates local sources of the particulate mass.

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