GAW Report No. 205 - IGAC Project

CHAPTER 3 - ASIAParticulate matter (PM) is the main pollutant of concern in Dhaka, Bangladesh, especiallyduring the winter months. There have been several studies to characterize atmospheric pollution inDhaka. Data are available for particulate matter, heavy metals, and trace gases [Salam et al., 2008and 2003; Mahmud, 2008; Bilkis et al., 2008 and 2004; Nasiruddin, 2006 - DoE, Government ofRepublic of Bangladesh].Salam et al. [2008] studied aerosol particulate matter (SPM, PM 10 and PM 2.5 ) and tracegases (SO 2 , NO 2 , CO and O 3 ) in Dhaka between January and April 2006. The total averageconcentrations of SPM, PM 10 and PM 2.5 were 263, 75.5, and 66.2 µgm –3 , respectively. The mass ofPM 2.5 is approximately 88% of the PM 10 mass, indicating fossil fuels as the main source ofparticulate matter in Dhaka. The total average concentrations of SO 2 , NO 2 , CO, and O 3 were 48.3,21.0, 166.0 and 28 µgm –3 , respectively. The total average concentrations of As, Cd, Cu, Fe, Pb, andZn in PM 2.5 were 6.3, 13, 94, 433, 204, and 381 ngm –3 , respectively. The measuredconcentrations for trace gases and metals were much lower than the ambient standard values forBangladesh.Begum et al. [2008] measured particulate matter (PM) in Dhaka (Farmgate), which is a hotspot (HSD) with very high pollutant concentrations due to its proximity to major roadways. Fineparticulate matter concentrations at HSD have decreased over this period (from January 2000 toMarch 2006) to less than half of the initial value, even with an increasing number of vehicles. Thisdecrease is likely the result of governmental policy interventions such as the requirement of vehiclemaintenance, training of repair workers, and phase-wise removal of two-stroke three wheelers fromthe roads in Dhaka. Other policy interventions include the banning of old buses and trucks fromoperating in Dhaka, promotion of the compressed natural gas, introduction of pollution controldevices on vehicles, control of emissions from industries, etc.Salam et al. [2003] studied aerosol chemical composition of atmospheric aerosol particles inDhaka under pre-monsoon conditions (March–April 2001). The elemental carbon (EC), organiccarbon (OC), organic acids, major inorganic ions, and trace elements were measured in TSP. Thereconstructed average particulate mass (TSP) was 516 µgm –3 . On average about 76% of theaerosol is from soil-type materials, around 18% from carbonaceous material, and around 6% aresoluble ions, and trace elements (without iron) are about 0.3%. Coal fly ash is likely a main sourcefor Cd, Pb, and Zn in Dhaka aerosol, while as appears to be of geogenic origin. High concentrationof elemental carbon and organic carbon concentrations were observed in Dhaka, e.g. about 22µgm –3 of EC and 45 µgm –3 of OC. The correlation between EC and OC was quite high (0.81)indicating a potential joint source of emission for carbonaceous aerosols. The EC/total carbon (TC)and K/EC ratios indicated that biomass combustion was not a main contributor to EC in Dhaka,which implicates that the fossil fuel combustion is the major contributor to EC levels in Dhakaaerosol.Nasiruddin [2006] reported the variation of the particulate matter (TSP, PM 10 , PM 2.5 ), andtrace gases (SO 2 and NO 2 ) from a continuous monitoring station on the premises of the nationalParliament Building, Dhaka. Annual average PM concentrations (PM 10 and PM 2.5 ) in the city ofDhaka showed a slight increasing tendency from April 2002 to July 2006 (2002 data is average ofconcentrations from April to December and 2006 data is average of concentrations from January toJuly 2006). Both PM 10 and PM 2.5 concentrations exhibit more than twice the national standards ofannual PM 10 (50 µg m -3 ) and PM 2.5 (15 µg m -3 ). Annual average concentration of SO 2 in 2003 (6.67ppb) is within the national ambient air quality standard of 30 ppbv. The annual averageconcentration of NO 2 in 2003 was 27.6 ppb, which is also bellow the annual ambient standardsvalue of Bangladesh of 53ppb. Khaliquzzaman [1998] reported the SO 2 concentrations were from64 to 143 µg m –3 at Dhaka (Tezgaon), where as NO 2 concentrations were between 25 and 32 µgm –3 at Dhaka (Farmgate) in 1996.The status and trend of the pollutionThe overall air quality situation in Dhaka, Bangladesh is improving day by day due to theawareness among the city dwellers and also due to control measures implemented by thegovernment of Bangladesh. The major achievements in improving air quality in Dhaka, Bangladesh87