Source Identification of Chittagong Aerosol by Receptor Modeling

Samples of fine and coarse airborne particulate matter (PM) were collected between February and July 2007 at the Continuous Air Monitoring Station (CAMS) in Chittagong, the second largest city in Bangladesh. Samples were collected using a dichotomous sampler in two fractions of < 2.5 mu m (fine) and 2.5 to 10 mu m (coarse). Samples were analyzed for elemental concentrations by proton induced X-ray emission (PIXE), hydrogen by proton elastic scattering analysis (PESA), and black carbon by reflectometry. Elemental data sets together with black carbon were analyzed by positive matrix factorization to identify the possible sources of mass for the coarse and fine PM fractions. Best solutions were found to be six and seven factors for elemental compositions for coarse and fine fractions at the CAMS at Chittagong, respectively. Sources were identified as biomass burning/brick kiln, soil dust, road dust, Zn source (including two-stroke motorcycles), motor vehicle, CNG vehicle, and sea salt. The PMF results show that about 35.5% of PM2.5 mass at this site comes from biomass burning. The second largest contribution of fine PM comes from motor vehicle including CNG vehicles. The third one is a Zn source that includes emissions from two-stroke vehicles and galvanizing factories with vehicles, probably the larger contributor of the two source types. In case of coarse PM, about 40% of PM2.5-10 mass comes from soil dust including road dust.