Air Pollution contamination of the atmosphere caused by the discharge, accidental or deliberate of a wide range of toxic substances. Often the amount of the released substance is relatively high in a certain locality, so the harmful effects are more noticeable. The major sources of air pollution are transportation engines, power and heat generation, industrial processes and the burning of solid waste. A new source of air pollution is an increasing 'hole' in the ozone layer in the atmosphere above Antarctica, coupled with growing evidence of global ozone depletion. Air pollution has also long been known to have an adverse effect on human beings, plants, livestock and aquatic ecosystem through acid rain.
Recently as in other parts of the world air pollution has received priority among environmental issues in Asia. This problem is acute in dhaka, the capital of Bangladesh and also the hub of commercial activity. The other urban areas like chittagong, khulna, bogra and rajshahi have much lesser health problem related to air pollution. In urban areas sometimes the houses are built on rocks and soils, which radiate radioactive gas from their basement. If this gas is inhaled for a long time it may cause lung cancer. In the rural areas of Bangladesh, the air pollution problems have not yet become a point of concern. This is due to fewer motorised vehicles and industries there. However, brick kilns and cooking stoves are the principal sources of emission in rural areas. In villages wood, coal, and biomass are used as sources of energy. Thus, it is likely that in those areas the principal air contaminants are particulate matter and volatile organic compounds (VOCs).
Basically, there are two major sources of air pollution in Bangladesh industrial emissions and vehicular emissions. The industrial sources include brick kilns, fertiliser factories, sugar, paper, jute and textile mills, spinning mills, tanneries, garment, bread and biscuit factories, chemical and pharmaceutical industries, cement production and processing factories, metal workshops, wooden dust from saw mills and dusts from ploughed land, and salt particles from ocean waves near the offshore islands and coastal lands. These sources produce enormous amount of smokes, fumes, gases and dusts, which create the condition for the formation of fog and smog. Certain industries in Bangladesh, such as tanneries at Hazaribag in Dhaka City, emit hydrogen sulphide, ammonia, chlorine, and some other odorous chemicals that are poisonous and cause irritation and public complaints. This may cause headache and other health problems.
With increased rate of urbanisation in the country, the number of vehicles is also increasing rapidly, and contributing to more and more air pollution. The Department of Environment (DOE), and other related organisations, have identified the two-stroke engines used in autorickshaws (baby-taxies), tempos, mini-trucks, and motorcycles as major polluters. At present, there are about 65,000 baby-taxies among them more than 296,000 motor vehicles ply in Dhaka City alone. Moreover, overloaded, poorly maintained and very old trucks and mini-buses are also plying the city streets emitting smokes and gases. In fact about 90% of the vehicles that ply Dhaka's streets daily are faulty, and emit smoke far exceeding the prescribed limit. Diesel vehicles emit black smoke, which contain unburned fine carbon particles.
The two-stroke engines are now discouraged in Bangladesh because of their pollution hazard. In view of the serious automobile pollution faced in the metropolis, an initiative was taken with World Bank support to introduce big buses in the city and discourage the ply' ing of small automobiles, including baby-taxis. The introduction of air-conditioned city bus service is an outcome of that initiative.
Sophisticated equipment is now being used to detect air polluters in Bangladesh. As such, four monitoring stations are set up at four divisional towns, namely, Dhaka, Chittagong, Khulna, and Bogra. In Dhaka the locations of vehicular emission test are at Tejgaon, Farmgate, Manik Mia Avenue, Gulshan, Lalmatia, and Agargaon. bangladesh university of engineering and technology (BUET) has also been conducting ambient air quality surveys since 1995.
The air quality standards are different for residential, industrial, commercial, and sensitive areas. The worst affected areas in Dhaka city include: Hatkhola, Manik Mia Avenue, Tejgaon, Farmgate, Motijheel, Lalmatia, and Mohakhali. Surveys conducted between January 1990 and December 1999 showed that the concentration of suspended particles goes up to as high as 3,000 micrograms per cubic meter (Police Box, Farmgate, December 1999), although the allowable limit is 400 micrograms per cubic meter. The sulphur dioxide in the air near Farmgate was found to be 385 micrograms per cubic meter, where as the maximum permissible limit is 100 micrograms per cubic meter. Similarly, in the Tejgaon Industrial Area the maximum concentration of suspended particles was 1,849 micrograms per cubic meter (January 1997), as opposed to the allowable limit of 500 micrograms per cubic meter. Usually the maximum concentration of air pollution in Dhaka is during the dry months of December to March.
The bangladesh atomic energy commission (BAEC) and the Bangladesh Council of Scientific and Industrial Research (BCSIR), in collaboration with the DOE, recently assessed the concentration of lead in the ambient air. The dhaka shishu hospital in association with the BAEC also estimated the level of lead in the blood of children of Dhaka City and the possible impact of leaded gasoline on them. The Bangladesh Road Transport Authority (BRTA) is also setting up a vehicle emission monitoring station at Mirpur, Dhaka.
Prior to introduction of unleaded gasoline, BAEC reported that the air that city dwellers breathe on the roads contains lead in concentrations almost ten times above the government safety standard set by the DOE. The air of Dhaka City holds 463 nanograms per cubic meter of lead - the highest in the world. From November 96 to March 97 the lead levels in three different areas of Dhaka City were 123-252 nanograms per cubic meter at Farmgate area and 61 to 76 nanograms per cubic meter in Tejgaon Industrial area.
The lead poisoning produces neuro-developmental disorders in children. About 50 tons of lead is emitted in the Dhaka air annually and the emission reaches its highest level in the dry season from November to January. Lead poisoning has been detected recently in children at the Shishu Bikash Kendro (Child Development Centre) of Dhaka Shishu Hospital. Lead concentrations, measured around 80-micrograms/dl-to180 micrograms/dl in the tested children's blood, is 7-16 times more than the acceptable limit. The safe concentration advocated by the US Centre for Disease Control and Prevention is 10 micrograms/dl. People living in urban slums have a significant rise in mean blood lead levels, compared to those living in urban middle-income or rural areas. The development of lead pollution could also affect the central nervous system, cause renal damage and hypertension. Excessive lead in the blood of children could damage-their brain and kidney. Children are three times more at risk than adults are by exposure to lead poisoning.
In Dhaka city the mean blood lead level of rickshaw pullers is 248 micrograms/dl (range 154-344 micrograms/dl), baby-taxi drivers 287 micrograms/dl, traffic police 272 micrograms/dl (range 152-32 micrograms/dl), tempo assistants 255 micrograms/dl, and petrol pump operators 249 micrograms/dl (range 207-342 micrograms/dl). The mean blood lead level among these risk groups is found to be higher than the acceptable value, with traffic police being the worst affected group. The blood lead levels usually increased with duration of exposure.
During July 1999 the Government of Bangladesh (GOB) executed the decision to provide only unleaded gasoline in the country. According to recent measurements between late 1999 and 2000 by BAEC and eastern refinery limited (ERL) the gasoline dispensed at pumps in Bangladesh is now totally free of lead.
It has been found that Dhaka city has VOC beyond tolerable limits, some of which cause cancer. Emissions from two-stroke auto-rickshaws in Dhaka were found to contain 4 to 7 times the maximum permissible level of VOC.
Dust pollution is causing many respiratory diseases, including asthma. Recently, 200 organic compounds are detected by analysing four air samples collected from the Shewrapara area of the city. As far as the VOC is concerned the following worst affected areas are identified: Hatkhola, Manik Mian Avenue, Tejgaon, Farm Gate, Motijheel, Lalmatia, and the inter-district bus terminals. Surveys conducted between December 1996 and June 1997 showed that the concentration of suspended particles goes up to as high as 2,465' micrograms per cubic metre as against the allowable limit of 400 micrograms per cubic metre at Farm Gate. In Tejgaon Industrial Area, on the other hand, the maximum con centration of suspended particles was 630 micrograms as against the allowable limit of 500 micrograms per cubic metre.
Mine air pollution a major issue of concern in Bangladesh. Dust and mine gases create problems for coalmine. Fortunately barapukuria coal of dinajpur district has insignificant gas content, therefore, in the process of mining of coal the danger of methane emission and methane gas related hazards are considered to be insignificant. As the Barapukuria coal will be mined mechanically, huge coal dusts would be generated but proper mitigation measures if taken coal dust could be controlled. Huge dusts will also be generated in the Maddhyapara hardrock mine in Dinajpur district, due to frequent movements of heavy vehicles together with required loading and unloading operations. The gases formed by the combustion of coal, fuel and lubricants in the mine both at the surface and underground pollute the ambient air. Dusts generated from coal and hardrocks especially during cutting, blasting, crashing and transportation in the mines are generally the cause of concern for the miners and for the surrounding localities.
Government decisions recently the Ministry of Energy and Mineral Resources (MEMR) has taken important decisions, which are as follows (i) the minimum standard of lubricating oil for two- stroke engine should be APITC or JASOEB and (ii) marketing of straight mineral oil should stop immediately.
In 1985-86 the bangladesh petroleum corporation started a project to use compressed natural gas (CNG) in vehicles instead of gasoline. The primary objective was to reduce vehicular emissions, as combustion of CNG produces less pollution than gasoline. The World Bank donated Taka 225 million to initiate the project. So far data on the number of vehicles converted to CNG from 1985 to 1997 are as follows: 1985-86 converted vehicles 2; 1988-89 converted vehicles 19; 1989-90 converted vehicles 9; 1990-91 converted vehicles 6; 1991-92 converted vehicles 10; 1992-93 converted vehicles 16; 1993-94 converted vehicles 3; 1995-96 converted vehicles 13 and 1996-97 converted vehicles 86. Private sector participation in using CNG for taxicabs is significant. At the beginning of 2002 the Government has started promotional campaign and appropriate push to the owners of autorickshaws to use CNG in order to reduce vehicular emissions.
Pollution policy the first regulation related to environment in Bangladesh was the Factory Act of 1965, which was followed by the earliest recorded environmental protection act, known as the 'Water Pollution Control Ordinance, 1970'. However, these ordinances do not include air pollution problems. Gradually these ordinances were modified and the Environmental Pollution Control Ordinance (EPC), 1977, was promulgated. It dealt with pollution of air, surface water and groundwater, and soil by discharge of liquid, gaseous, solid, radioactive, or other substances. Although the order passed under the EPC 1977 was legally in place, implementation of environmental laws never took place.
Following rapid industrialisation the environmental scenario in Bangladesh changed dramatically. The Ministry of Environment and Forest and the Department of Environment were created in 1989 and the Environment Policy of 1992 was introduced. Further, the Environmental Conservation Act, 1995, and the Environment Conservation Rules, 1997, were approved by the Bangladesh National Assembly to restrict and mitigate ever-growing environmental problems in the country. [Sifatul Quader Chowdhury]
Bibliography United Nations Environment Programme, State of the Environment: Bangladesh, United Nations Environment Programme, 2001.