Air pollution in Dhaka City

Problems and Remedies

 Dr. Jamal Anwar


Dhaka Statistical Metropolitan Area has now extended to more than double the area of what existed in 1981, and by the end of the century, with a population of 11.2 million, it will rank seventeenth among the mega cities of the world. Unplanned growth of Dhaka city has already created adverse ecological effects. According to Asian Development Report 1998, Dhaka is the most polluted city of the world. 

There is no quantitative air monitoring station in Dhaka but a few scattered studies show the alarming situation. The Environmental Pollution report ’98 of the Department of Environment (DoE) describes that Suspended particulate Matter (SPM) in the air is between 1000 and 2000 microgram, four to five hundred percent higher than the acceptable level. The size, shape, and density of an airborne particle determine how long a particle will remain in the atmosphere, whether or not it will be inhaled, and where it may be deposited in the respiratory tract. The solubility of a gas determines (in part) whether it will cause upper airway irritation or pulmonary edema. The particulate material can also absorb gases (including sulphur dioxide and formaldehyde) on surface. 

The highest acceptable level of sulphur dioxide (SO2) is 60 microgram per cubic meter of air. But it has been recorded at 300 to 500 microgram in Dhaka. The amount of nitrogen is also three times higher than that of normal. Bangladesh Atomic Energy Commission reports that automobiles in Dhaka emit 100 kg lead, 3.5 tonnes SPM, 1.5 tonnes sulphur dioxide, 14 tonnes hydrocarbon and 60 tonnes carbon monoxide. 

Concentration of lead in ambient air of Dhaka city has been marked as world’s record of 463 nanogram (ng-one part per billion) per cubic metre offsetting earlier record of Mexico city (383 ng) and other cities like Kyoto (49 ng) and Los Angles (70 ng). Gaseous and particulate emissions moved downwind either by direct absorption on precipitation or by deposition on surfaces. Many of the pollutants deposited dry on the surface return to hydrological cycle during the next rainfall as they are washed from the surface. A local Bangla daily on its March 10, 1997 issue reports a very high content of lead in fish at Dhanmondi Lake and advices to stop consuming fish. The University of Engineering (BUET) found 151 to 210 mg lead per liter in Dhanmondi Lake. It is most likely that most of the wetlands surrounding Dhaka city are extremely polluted. 

The average suspended particle leads to particulate matter (PM) rises as high as 227 mg per cubic metre, whereas, according to WHO, annual maximum average value should range between 60-90 mg per cubic metre. 

Monitoring air pollution is inadequately carried out in Bangladesh due to the absence of trained personnel and modern laboratory equipment. There is a great concern about the role of air quality in cancer mortality incidence. 

Multiple chemical interactions of air pollutants 

The pollutants are complex mixtures of chemicals solubilised in air, chemicals solubilised in aerosols and chemical particulate. The general consensus unscientific literature is that health decreases with increasing air pollution. Increased human moralities have been associated with the elevated air pollution, elevating total suspended particles and SO2 by 10 ug/m3 increased mortality by 7 and 5 per cent respectively. High level concentrations both SO2 and SPM is particularly hazardous to health giving rise to increase mortality and morbidity. 

In air pollution, air is the vehicle that conveys pollutants to biota. The chemistry of the pollutants in air is a dynamic process. For example, SO2 emissions are converted to sulphate, sulphuric acids, ammonium sulphate, ammonium bisulphate, and when inhaled, these compounds have properties of particulate. Hydrocarbon pollutants are oxidised and the oxidation products are important in the production of troposphere ozone. 

Photochemical are produced by ultraviolet light-activated reactions ultraviolet light activated reactions of atmospheric pollutants. Briefly, nitrogen dioxide (NO2) when activated by ultraviolet light, undergoes photo oxidation to produce nitric oxide (NO) and atomic oxygen (O-1). The O-1 combines with diatomic oxygen (O2) to form (NO2). The O3 is used up by the reaction with nitric oxide to form nitrogen dioxide. Hydrocarbon pollutants especially olefins and substituted aromatics, react with oxygen to form free radicals. The free radicals reacts with nitric oxide to form nitrogen dioxide. 

Low level exposure effects have been done in humans on photochemical products. Concentrations of 100 ug of photochemical products/m3 causes headaches, 300 ug/m3 is irritating to the eyes, 510 ug/m3 is irritating to the respiratory tract and produces cough, and 580 ug/m3 produces chest pain. Moralities in Los Angeles area increase when atmospheric increase when atmospheric photochemical products reached levels ranging from 0.5 to 0.9 ppm. 


Ozone is generally short-lived at ground level. But once formed, the reservoir can replenish O3 at ground level for 2 or 3 days. The toxic effects of O3 in the lower regions of the respiratory tract increase with increased minute respiratory volume. Animal and human test exposed to O3 shows pulmonary injury and pulmonary function decreases ranging from 12.6 to 20.7 per cent. Ozone comprises the native resistance of the lungs to disease. 

Acidification of soil and water 

Soils around Dhaka is deficient in lime and acidification of soils and water has crated diverse damage to ecological system. Acidification causes: 

·        Diminish in organic (humus) content in soil;

·        Greater solubility of many metals including aluminum;

·        Elimination of fish;

·        Essential metals and nutrients are leached out to ground water,

·        Loss of vegetation. 

Sources of Emission 

About 200,000 motor vehicles ply in Dhaka. In industrial countries lead added gasoline driven cars are almost disappearing and at the same time these harmful automobiles are exported to the developing countries in the name of “reconditioned cars”. In recent years due to reduced tax these cars have conquered Bangladesh market. 

Three wheelers or two-stroke engine (auto-rickshaws) driven vehicles emit poisonous gases as these engines have very low efficiency to burn hydrocarbon. Hydrocarbon  such as benzo (a) pyrene are produced by incomplete combustion. bezo (q) pyrene is classified as a  proven carcinogen which in process encompassing the conversion of normal cells to neoplastic cells into a tumour. Auto richshaws are also using “processed burn-mobil oil” in their engines. It is known in industrial countries that recycled old oils may contain many extremely carcinogen constituents like Polycyclic Aromatic Hydrocarbon (PAH), Dioxins etc. Besides “local mixtures” with many cheaper varieties practised in Bangladesh may crate more serous health hazards. 

More than 80 per cent of the vehicles of the city are totally unfit to run on the streets. (Department of Environment, 1988). More than 50 per cent of the vehicles, moving in the city under the shadow of invisible power, have no authorised papers and they never  bother to have any (a comment of an official of the Bangladesh Road and Transport Authority, 1988). 

Brick-producing plants in and around Dhaka are producing one of the worst hazardous emissions of this planet. Apart from the destruction of valuable topsoil and palm and bamboo trees of the country, a highly poisonous mixing procedure has been developed by the brick-manufactures for the furnace at the cheapest  cost. They use trees, coal of very low quality (more than 10 per cent sulphur, very high ash content etc.), used types (contain PCB), and used tyres (contain PCB), and used oil to obtain optimal temperature for burning bricks. 

The “used oil” is one of the most hazardous wastes that costs million of dollars for disposal in the industrial countries  The present writer visited (January, 1987) the ship-breaking sites at Patenga, Chittagong, electrical transformer repairing workshops and old oil selling centres where a huge amount of old oil of different sources are collected and sold to brick-manufactures and local grocery shops. Along with old ocean going vessels a huge amount of hazardous oil is imported from the industrial countries. The old-oils extracted from transformer oils, hydraulic fluids, automobiles and the like are sold locally named “Maita Tel” or “soil-oil” and used in households as insecticide for protecting wood or metal from rust. Among other hazardous chemicals PCBs are synthesised derivatives of the compound bi-phenyl, and complex mistures of various isomers and they are very resistant and stable in environment and do not breakdown over time when exposed to heat, sunlight, water, and or biological/chemical reactions. Especially dangerous is PCBs biological persistence. PCBs may remain in the fat cells of organisms (including man) for the life of the organisms. PCBs related hazard are: 

·        PCB’s contain, furans, dioxins, napthalenes (carchinogen)

·        Absorbed by skin, respiratory tract and alimentary tract

·        Concentrated in lipids

·        Concentrated in food chains Chlorine – severe and persistent acne-like rash. Liver damage

·        Suppress immune system and nervous system

·        Increased growth of cancer

·        Birds reduced hatchability and toxicity of the embryo.

Ambient air of Dhaka has become a deadly pollutant reaching a level of all times and it can be declared as one of the worst polluted cities of the world. Eight million vehicles runs in Los Angeles show lead content between 0-70 nanogram (part ber billion) lead content in cubic metre, whereas Dhaka with 200,000 vehicles has been marked as world record of 463 nanogram (one part of a billion). Environmental researchers attribute the pollution to vanishing green trees making way for concrete structures, unabated growth of industries and brick fields in city are, two-stroke engine vehicles and dumping of garbage on roadside.

 Immediate actions for better air in Dhaka requires: 

·        Prevention of emission at source

·        Use of compressed natural gas (CNG) instead of petrol or diesel

·        Motorise vehicle free areas in the city

·        Improve mass transport service ban two-stroke engine

·        Use of natural gas for burning in the brick-fields.

  Source: Observer Magazine, February 9, 2001