Assessment of trends and present ambient concentrations of PM2.2 and PM10 in Dhaka, Bangladesh

The present air quality has been studied at two air quality monitoring stations in Dhaka, the capital of Bangladesh. One site at the Farm Gate area is a particulate matter (PM) hot spot (HSD) with very high pollutant concentrations because of its proximity to major roadways. The other site is in a semi-residential area (SR) located at the Atomic Energy Centre, Dhaka Campus with relatively less traffic. The samples were collected using a 'Gent' stacked filter unit in two fractions of 0-2.2 and 10-2.2 mu m sizes. Samples of fine (PM2.2) and coarse (PM10-2.2) airborne particulate matter collected between 2000 and 2005 were studied. It has been observed that fine particulate matter concentrations at the HSD have decreased from over this period to less than half of the initial value even with an increasing number of vehicles. This decrease is likely the result of governmental policy interventions such as the requirement of vehicle maintenance, training of repair workers, and phase-wise removal of two-stroke three wheelers from the roads in Dhaka with a complete ban of their commercial use beginning on January 1, 2003. Other policy interventions were banning of old buses and trucks from operating in Dhaka, promotion of the compressed natural gas, introduction of pollution control devices on vehicles, control of emissions from industries, etc. It was found that both local (mostly from vehicular emissions and seasonal brick kilns) are responsible for the high PM2.2 and black carbon concentrations in Dhaka. PM2.2, PM10-2.2, and black carbon concentration levels depend on the season, wind direction, and wind speed. PM10-2.2 has not been the focus of policy decisions, and the decrease in concentrations has been much smaller than were observed for the PM2.2. There is also some indication of the role of transport of PM2.2 from regional sources.