Abstract:
Dhaka, the capital city of Bangladesh, the ninth largest and seven most densely populated city with a population of about 21 million people, is exposed to extremely unhealthy levels of ambient air pollution. Recent insights in the field of air quality of Dhaka city reveals that transboundary pollution contributes significantly to the concentration of fine particulate matters during dry season. Additionally, contribution from local emissions i.e. brick kilns, vehicular sources, re-suspended road dust etc. also plays a crucial role. A fully calibrated air dispersion model assessing the effect of present pollutants and quantifying mitigation benefits, can be an effective impact prediction and policy analysis tool for air quality management. The central focus of this study was to assess how well AERMOD (American Meteorological Society (AMS)/EPA Regulatory Model), the USEPA preferred regulatory model perform in modelling the air quality of Dhaka city considering Brick Kilns and vehicular sources, identifying vulnerable zones in terms of air pollution and quantifying impact of different mitigation strategies like conversion of existing brick kilns to Zigzag or Improved Zigzag Kilns on the air quality of Dhaka City.
To establish an air quality model of Dhaka city, Brick kilns and traffic emissions were considered to calculate the concentrations of particulate matters for various averaging periods. Modelled data was validated via comparing with measured concentrations from three Continuous Air Quality Monitoring Stations (CAMS) located inside the city. Letter, different scenarios were generated to predict the maximum concentration contour Map outputs using Uniform Cartesian Grid Receptors option for PM2.5 and PM10. The two scenarios considered were as follows: Scenario I: Models considering Birck Kilns from different districts near Dhaka City and identifying the major contributing district, and Scenario II: Impact assessment if all the FCK Kilns are converted to TZK and IZK Kilns considering greater Dhaka extent.
Contribution of brick kilns showed an average contribution of 44% and 34.1% of the total ambient concentrations for PM10 and PM2.5 respectively, while traffic contributions were found much less contributing compared to brick kiln contributions for both the pollutants
Brick kilns situated in the Dhaka district significantly contribute to PM10 pollution followed by Narayanganj, Gazipur and Munshiganj district.
The conversion of all existing brick kilns to Zigzag technology showed a satisfactory reduction (almost halve) in emissions, while the transition to Improved Zigzag Kiln (IZK) technology promises to be even more beneficial, further reducing the highest concentration to a minimal value.
Modelled results for fine particulate matters would meet the measured concentrations approximately if multiplied with a factor of three, suggesting significant contribution from transboundary sources. While the conversion to Zigzag and IZK technologies can significantly reduce local emissions from brick kilns, a substantial proportion of the emissions in Dhaka city originate from neighboring countries and other districts of Bangladesh. Therefore, a comprehensive and coordinated local and regional approach will be essential to effectively mitigate air pollution in Dhaka city.