Air quality assessment and the health effects of air pollution in Dhaka city through impact-pathway model

Abstract

Dhaka, the capital city of Bangladesh, with a population density of around 20,000 per square kilometer is at the risk of experiencing significant health impacts from poor air quality, especially during the dry season. The economic cost associated with urban air pollution is estimated to be around 1.1% of national GDP. Recently, the Government introduced a number of initiatives such as banning of twostroke engine vehicles, promoting the use of alternative fuels like CNG, banning of old vehicles from plying on streets, in order to curb the growing air pollution problem. Though some improvements have been observed, such policy decisions are taken on adhoc basis and there is a lack of benefit modeling to support these decisions due to limited monitoring and limited analysis of the options. Currently, the institutions lack an integrated policy analysis tool to help the decision makers evaluate alternate air pollution management strategies and analyze costs and benefits. This research aims to fill this gap, by developing a policy analysis tool for Dhaka to better understand the impact of various abatement measures and potential for environmental benefits. The tool is designed to follow the impact pathway approach linking the changes in emissions with changes in ambient concentration, especially particulate matter (PM) and related health impacts - mortality effects and the associated monetized benefits. A grid based source-receptor matrix over Dhaka has been developed using an atmospheric dispersion model, considering temporal variations in emissions and weather parameters round the year. The contributions from major sources (vehicles, and brick kilns) have been considered in determining the ambient PM concentrations; both spatial and temporal variations of PM have been estimated. In the Dhaka city the PM10 concentrations in dry season has been estimated to be less than 50 μg/m3 to about 150 μg/m3. The range of PM2.5 concentration in the city has been estimated in between 25 μg/m3 and about 65 μg/m3. Near the National Parliament Building, where CAMS (air quality monitoring station) is located, brick kiln has been found to be the major source of particulate pollution with 43% contribution to PM10 concentration and 21% contribution to PM2.5 concentration. Traffic pollution contributes 10% to PM10 concentration and 13% to PM2.5 concentration at that specific site. However, the sourcereceptor matrix could be easily utilized to obtain ambient concentrations as new sources are added/removed from the domain. Particulate related health impacts have been evaluated utilizing established concentration-response functions for mortality due to pollution exposure. Moreover, the monetary value of these health impacts due to traffic and brick kiln emissions are estimated. Finally, the study presents case studies under “what-if” scenarios for multiple policy alternatives using the developed policy assessment tool for Dhaka. It has been found that significant health and economic benefits could be achieved with policy interventions aimed at improving air quality.