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Chemical Speciation of Particulate Matter Pollution in Urban Dhaka City
Mahbubul Islam; p.51-58, Bangladesh Environment 2000, A compilation of Papers of the International Conference on Bangladesh Environment –2000 (ICBEN-2000), BAPA.

Abstract

Dhaka, the capital and largest city of Bangladesh, lacks a regular air pollution monitoring network to measure and assess ambient air pollution level. Several academic and research projects attempted to measure a limited number of air pollutants near roadways in the central business district. These studies revealed that ambient concentrations of lead, benzene, particulate matter, carbon monoxide, oxides of sulfur, and nitrogen in the air of Dhaka have exceeded health based standards set by both the World Health Organization (WHO) and United States Environmental Protection Agency (US EPA). The measured peak concentrations for some pollutants were found to be several folds higher than the international standards. In one instance, a study conducted by the Bangladesh Atomic Energy Commission showed that Dhaka's ambient lead level was highest in the world for a part of the year 1996.

With the assistance of World Bank, Bangladesh Department of Environment (DOE) recently began an air quality management project in the Dhaka City. An international consultant helped the DOE personnel to setup an air-monitoring network in selected locations of Dhaka City to collect and measure particulate emissions. This paper presents results of the chemical analysis conducted on the ambient filters collected by the World Bank and DOE monitoring effort. Due to financial constraint, the World Bank and DOE limited their objective to only measurement of the level of ambient particulate concentrations. However, without a detailed chemical speciation of the collected filter, it is not possible to identify pollution sources and their relative contributions. Furthermore; in order to understand public health implications and asses exposure risks, chemical components of the particulate pollution must be known. In a joint effort, the Bangladesh Environment Network (BEN) and the international consultant for the Dhaka air quality management project arranged for the laboratory analysis of the collected filters. The world renowned Desert Research Institute (DRI), Reno, Nevada, conducted chemical analysis of the filters. Dr. Judith Chow of DRI, who pioneered many chemical techniques for analysis of particulate pollution, graciously offered the service to analyze these filters at no cost.

Among the sampling sites, the Farmgate site has shown the maximum ambient level, as high as 526 microgram of PM2.5 per cubic meter of air volume. This level is more than eight folds higher than the US EPA standard of 65 microgram per cubic meter. The fine PM2.5 size pollutants are primarily emitted by combustion processes and automobile emissions. As Farmgate is considered one of the most congested traffic intersections in Dhaka, such an extremely high PM2.5 level is the direct result of vehicular emissions.

The chemical analysis of the filters at DRI laboratory identified presence of the following chemical species in the Dhaka’s particulate air pollution: elements of sodium (Na) to lead (Pb), chloride (Cl-), nitrite (NO2-), nitrate (NO3-), sulfate (SO4-2), ammonium (NH4+), organic carbon (OC), elemental carbon (EC), etc. Very high concentrations of sulfate, organic carbon, led, nitrate, etc. suggest that particulate emissions are predominately formed by the combustion products of dirty fuels (i.e., high sulfur diesel and leaded petrol) used in automotive engines.

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