Identification of Sources of Fine and Coarse Particulate Matter in Dhaka, Bangladesh

Abstract

In Bangladesh, the ambient air within Dhaka city is highly polluted by motor vehicle and brick kiln emissions. In addition, meteorological conditions during the winter cause increases in the fine particulate matter concentrations by factors of 4 to 5 fold compared to the rainy season. To understand the contribution of possible pollution sources, compositional data for both the coarse and fine fractions samples collected between May 2001 and March 2005 have been analyzed using Positive Matrix Factorization (PMF). The results were compared with the previous source apportionment results. Conditional Probability Function (CPF) plots were developed for each source using local wind data to explore the directionality of local sources. Back trajectory ensemble methods were used to identify potential source regions and pathways of transboundary transport of PM2.2 apportioned sources. The Potential Source Contribution Function (PSCF) domain extended around the receptor site in Dhaka (23.77°N, 90.38°E) over the range from 1.5° to 42.5°N and 56.5° to 110.5°E. The PSCF results are compared to the conditional probability function (CPF) analyses that use 3 hour average local wind directional data to determine the likely directions for the sources. Both PSCF and CPF help to identify the potential source locations, but on different distance scales. These analyses demonstrate that coarse particles are dominated by local sources. However, local and regional source contributed to the elevated fine PM levels in Dhaka. Thus, regional control efforts will be required in addition to local initiatives to improve the air quality in mega cities in this region like Dhaka.