Characteristics of atmospheric trace gases, particulate matter, and heavy metal pollution in Dhaka, Bangladesh

Abstract

Aerosol particulate matter (PM10 and PM2.5) and trace gases (SO2, NO2, CO and O3) were sampled at five locations in greater Dhaka, Bangladesh, between January and April 2006. Particulate matter was collected on micro-fiber filters with a low-volume sampler, and trace gases (SO2, NO2, and O3) were collected with an impinger equipped with PM samplers. Carbon monoxide was determined using the Indicator Tube method. The total average concentrations of SO2, NO2, CO, and O3 were 48.3, 21.0, 166.0 and 28 μg m–3, respectively. The total average concentrations of SO2 and NO2 were much lower than the annual average guideline values of the World Health Organization (WHO). The total average O3 concentration was also much lower than the daily maximum values established by WHO (average of 100 μg m–3 for an 8-h sample). The total average concentrations of five sites were 263, 75.5 and 66.2 μg m–3 for SPM, PM10 and PM2.5, respectively. The mass of PM2.5 is approximately 88% of the PM10 mass, indicating that fossil fuel is the main source of PM in Dhaka. An atomic absorption spectrophotometer was used to determine the heavy metal concentrations in the PM2.5 size fraction. The total average concentrations of As, Cd, Cu, Fe, Pb, and Zn in PM2.5 were 6.3, 13, 94, 433, 204, and 381 ng m–3, respectively. The Pb concentration in Dhaka shows a decreasing tendency, presumably due to the ban on the use of leaded fuel. The overall trace metal concentrations in Dhaka are higher than those in European (e.g., Spain, Norway) and East Asian (e.g., Taiwan) locations, but lower than those measured in Southeast Asian (Kanpur, Delhi, Mumbai, India; Lahore, Pakistan) cities.