Key Issues for Control of Air Pollutants in Dhaka Bangladesh

Bilkis A. Begum (1), Swapan K. Biswas (1), Philip K. Hopke (2)

(1) Chemistry Division, Atomic Energy Centre, Dhaka, Bangladesh (2) Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY

     Abstract Number: 23
     Last modified: September 29, 2009

Abstract
Air pollution in Dhaka, Bangladesh, like other mega cities in Asia, has drawn the attention of Government and the public over last few decades. Policy interventions have been initiated to improve the air quality. Recent studies show that particulate air pollution is a major problem, and thus, it is necessary to understand the characteristics of the pollutant and the sources to permit further improvements in air quality. Particulate matter (PM) (both coarse and fine fraction) sampling was performed in a semi-residential site (AECD) in Dhaka from February 2005 to December 2006. The samples were analyzed for mass, black carbon (BC) and elemental composition. This data set was analyzed for sources using EPA-PMF. Previous work had shown that particulate matter concentrations become worse during the wintertime than the rainy season. Therefore, to determine the seasonal source contributions, EPA-PMF modeling was also applied to seasonally segregated data. The coarse PM mass is about four times higher in wintertime than during the rainy season. It is also observed that during the wintertime, soil dust together with road dust contributes 60% of total coarse PM mass and these contributions are cut in half in the rainy season. Brick kilns contribute only in the dry season and account for about 25% of the coarse mass and 30% of the fine mass. Because of the brick production technology used in Bangladesh, brick kilns are operated only in wintertime. In the winter, the contribution from motor vehicle emissions is about 34% fine mass whereas in rainy season this contribution reduces to about one-fourth. Thus, the high contributions in dry season from fossil fuel combustion and brick kiln operation in Dhaka are enhanced by the seasonal meteorology since winter is relatively dry and wind speeds are minimal. To explore long range contributions, the source contributions for brick kilns and fossil fuel combustion were evaluated. The highest fine fraction PM contributions were was identified be examining the values above the 95th percentile. Transboundary events were observed on December 14 2005 and January 16 2006. Satellite images showed that a haze consisting of mixed pollution and fog was at the base of the Himalayas in India in late December 2005. High air pollution is common in this region between December and February and it often accumulates at the base of the mountains. These pollutants may be then transported over long distances contributing to local air pollution.
From the source apportionment results, it is observed that vehicular emissions and emission from brick kiln are the major contributors to air pollution in Dhaka especially in the dry seasons. The Government of Bangladesh is trying to reduce the emission from both the sources by encouraging the conversion of diesel/petrol vehicles to CNG and by introducing green technologies for brick production. However, the transboundary impacts will require international action.