Concentrations and source apportionment of PM(2.5) monitored at an urban residential site in Karachi Metropolitan, Pakistan have been reported in this paper. PM(2.5) aerosol samples were collected on alternative days (three times per week) for 24-hrs duration on Zefluor(TM) filter papers using Thermo-Electron Corporation Reference Ambient Air Sampler (RAAS). A total of 402 samples were collected from January 2006 to January 2008. According to results high PM(2.5) loads were observed in post monsoon months that is about 2 times than those observed in the summer and monsoon seasons in the yearlong measurements. The collected samples were analyzed using ICP-MS for trace metal concentration. Source apportionment was performed on PM samples using Positive Matrix Factorization (PMF) model. The results derived from PMF model indicated five (05) major contributors to PM(2.5) in Karachi which were: soil/road dust, industrial emissions, vehicular emissions, sea salt originated from Arabian Sea and secondary aerosols.
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