Abstract
Fine and coarse PM10 samples collected in Hanoi in 1999-2001 were analysed for black carbon (BC) and water soluble ions (WSI) and measured data were disaggregated according to three types of back trajectories, namely 1) northerly, over inland China, 2) northeasterly, over East China Sea and, 3) southwesterly over Indochina peninsula. Types 1, 2 and 3 trajectories prevail in September/October-December, January-March/April and May-August, respectively. Source – receptor modelling was performed for each type of trajectories individually using the Positive Matrix Factorization (PMF) technique. Six or seven sources were extracted for each trajectory type including soil dust, primary and secondary emissions from local burning (LB), vehicle/road dust, sea salt, Cl-depleted marine aerosols and long range transport (LRT). LRT contributes little to the coarse mass, but accounts for 50%, 34% and 33% of the fine mass in trajectory types 1, 2 and 3, respectively. More than two-thirds of the fine mode sulphate are attributed to LRT and associated with ammonium. Major contributors to the coarse mass are soil dust and LB primary emissions. Coarse mode sulphate was found mainly in soil dust and LB emissions. The comparison of LRT and LB source profiles suggests that air masses arriving from north-northeasterly trajectories are more polluted than those coming from the southwest. Also, LRT aerosols originate from coal and biomass burning, while LB emissions are dominated by coal burning. Various mechanisms of sulphate formation in LRT and LB were suggested based on the concentration ratios of [S O4 2- ]/[K + ], [S O4 2- ]/[BC] and [N H4 + ]/[S O4 2- ] for the two sources.
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