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Because of increasing use of vehicles and other human activities in metropolitan Colombo, Sri Lanka, a study of long– term airborne particulate monitoring at two fixed sites was initiated. The specific objectives were to measure the elemental composition of the coarse and fine air particles, to identify the trends in pollution, to identify the main pollutant sources, and to quantify the source contributions. Samples of airborne particulate matter (PM) in the < 2.5 and 2.5–10 µm size ranges (PM2.5 and PM10–2.5) were collected using “Gent” stacked filter samplers at two urban sites in Colombo. The Air Quality Monitoring Station (AQM) of the Central Environmental Authority (CEA) operated during the period of May 2000 to December 2005. The second site at Atomic Energy Authority (AEA) operated from May 2003 to December 2008. Twenty–four hour samples were collected on weekdays. The fine filter samples were analyzed for 18 elements by ED–XRF. The annual averages for PM10, PM2.5, and black carbon (BC) at the AQM station during 2000 – 2005 ranged from 50 to 100, 16 to 32, and 8 to 15 µg/m3, respectively. The fine fraction data set including BC and major elements (Na, Mg, Al, Si, Cl, Fe, Zn, Ni, Cu, V, S, Br, Pb, Cr, K, Ca and Ti) was analyzed using EPA–PMF (Positive Matrix Factorization) to explore the possible sources of the PM at the two study sites. Four factors were found at both sites. The common sources are motor vehicles, road dust, biomass and sea salt. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPILT) back–trajectory model was used to explore possible long range transport of pollution. Smoke and soil dust transboundary events were identified based on fine Si and K in the data base in 2003 and 2004.