Not only the capital city,Dhaka is also the center point of business activities in Bangladesh. For this, people from all over this country always look forward to shift here. The population of Dhaka is increasing tremendously every year, it is recorded as one of the most populous cities in the world and therefore it is almost impossible to maintain a clean and sustainable environment.
Dhaka has positioned top several times among cities with worse air quality index (AQI) that indicating very unhealthy environment. Urbanization, industrialization, and motorization cover the significant part of the total percentage of air pollution. This paper investigates on the data of population increasement, harmful emissions from brick kilns and other industries, registered and unregistered vehicles, different significant polluting agents such as CO (Carbon Monoxide), Pb (Lead), PM2.5 (Particular Matter), PM10 (Particular Matter), CO2 (Carbon Dioxide), NOx (Nitrogen oxides), SO2 (Sulfur Dioxide), O3 (Ozone), HC (Hydrocarbon) for the last ten years. By analyzing this information the result describes how the air pollution has become a notable reason for the rising mortal rate in Bangladesh. This paper explores the existing quality of air and the effects of pollution in Dhaka city.
The current population of Bangladesh is around 160 million, equivalent to 2.11% of the total world population . Being the center of economic, cultural, and academic activities, air pollution is the greatest among all cities in this extremely populated nation. As stated in the ‘Bangladesh Bureau of Statistics 2014’, among all the densely populated cities in the world, Dhaka ranks four having a population density of about 28,000/ km². At present, it has become an unacceptable place to live in for the highest air pollution, and according to AirVisual, Dhaka has been ranked one of the leading towns owning the most polluted air in the world  Numbers of deaths in Bangladesh due to air pollution from 2000 to 2017 is shown in Fig.1.
Following Worldatlas, Bangladesh ranks 6th position for the premature pollution-related deaths per year, and 207,922 deaths take place concerning this issue . An estimation declared air pollution to be the reason for the death of seven million lives worldwide every year .
Air Quality Index delivers information on air quality daily of any city or country. How clean or polluted the air is, and the associated health concerns can be predictable from AQI data .
The report “State of Global Air 2019” states that “Air pollution is the 3rd leading risk factor for mortality in Bangladesh, accounting for approximately 14% of deaths (123,000) in 2017 alone.” Individually, household air pollution and outdoor air pollution are ranked as the 4th and 8th leading risk factors . Around 72% of national household use solid fuel, which contribute to air pollution . It is also reported there are ten major risk factors for death and disability in Bangladesh in 2017 and air pollution is one of them.
To observe major air pollutants which are Carbon Monoxide, Nitrogen Dioxide, Ozone, Sulfur Dioxide, PM10, and PM2.5 and generate real-time air quality data was the main objective of this prolonged project. The data includes air quality index by developing 11 Continuous Air Quality Monitoring Stations (CAMS) installed in Dhaka, Narayanganj, Gazipur, Chittagong, Rajshahi, Khulna, Barisal, and Sylhet . The project focused on two components-Environment by addressing emissions from brick kilns, and Transport by including traffic management and engineering issues to regulate emissions .
In a report of the ‘1st National Conference on Environmental Health’ by Akhtar Ahmed, held in Bangladesh in the year 2002, revealed that the factors behind air pollution in Bangladesh are different automobiles, industrial emissions, bad civic practices along with underprivileged government services .
According to Bangladesh Road and Transport Authority (BRTA), each year almost 37,000 cars are added in Dhaka, of which 80% are private cars. Nearly 10% of Dhaka’s commuters own one private car, which is increasing every day . There were 1 million registered motor vehicles in September 2016 in Greater Dhaka. And 400,000 unregistered motor vehicles are also running on the roads of Dhaka . In Table.1 some data of the total numbers of different types of vehicles in Dhaka from 2015 to 2019 is shown.
Traffic jam shares 58.6% and industrial sources release 15.7% of the total annual NOx emissions. And CO emissions from automobiles share 40.5% of the total CO emissions, while 27.1% from fossil fuels, 16.4% from brick kilns and other industries .
Air pollution is characterized by the presence of PM in atmospheric air. Particles float in the air, caused by dust and combustion, is known as suspended Particulate Matter (SPM), a significant reason for air pollution .
Substances of 10 micrometers in size or smaller (gas and solid) are Particulate Matters PM10. These substances are severe health hazards. Annually each brick kiln emits 83 tons, steel re-rolling mills 17 tons, cement factory 130 tons, and ceramic factory emits 20 tons of PM10 . In Fig.2, PM quantity in some countries (India, Pakistan, China, Australia and USA) are compared with that of Bangladesh showing that the PM quantity is always greater than any other country shown here.
The people should be treated as the asset of any country. But in Bangladesh, it has been considered as one of the greatest problems which is getting worsen day by day. The total population of Bangladesh is almost 160 million (160,000,000) and nearly 10 million people live only in Dhaka . In Fig.3 the increasement of population in Bangladesh from 2008 to 2019 is shown.
The area of Bangladesh is 147,570 km². It can be seen that around 6.25% of the total population are living in Dhaka. Total land area of Gazipur (1,806.36 km²) is greater than that of Dhaka (1464 km²) but the population is very much high in Dhaka district (10,356,500) in comparison with Gazipur (3809000). The population density is very much high in Dhaka than any other cities Bangladesh. Lack of awareness, illiteracy, preconception, the expectation of male child and many other reasons are behind the high growth of the population in Bangladesh.
Brick kiln industry is the biggest source of air pollution in Bangladesh. There are almost 7900+ brick kilns in Bangladesh and around 1000 kilns are only in Dhaka . Most them use coal and wood as the major sources of energy consistently producing black smoke having Particulate Matter, oxides of Carbon and Sulfur, and volatile organic compounds . Fig.4 shows that every year in Bangladesh, Carbon Doxide emission has been increasing in a linear pattern.
The energy-efficient kilns are hybrid Hoffman, and tunnel kiln should be used to reduce harmful emissions. As reported in Sustainable and Energy Efficient Brick Production Roadmap in Bangladesh, in 2019, 91% of bricks produced in Bangladesh are made using highly polluting traditional firing technology, Fixed Chimney and zig-zag . And in 2018, the overall percentage changed in 70% zig-zag kiln, 28% Fixed Chimney, and 2% modern technology . Each year around 100 million tonnes of topsoil was used to manufacture 25 billion pieces of conventional clay bricks resulting in 20 million tonnes of Carbon Dioxide annually as a byproduct. Moreover, the Brick Production and Brick Kiln Building (Control) Act 2013, was amended in 2019. The DoE says 71.64% brick kiln use technology that reduces emissions .
Various industrial processes like petroleum refineries discharge a large amount of Carbon Monoxide, nitrous oxide, hydrocarbons, organic compounds, and chemicals into the air. . Bangladeshi leather industries were set up mainly in Hazaribagh, located southwestern of the capital city Dhaka enlisted as one of the top ten most polluted places in the world . Almost every leather tannery uses metal-containing chemicals in the process of converting animal hides into leather .
The combustion of fossil fuels like coal, Petroleum and other factory combustibles results in emitting Carbon Monoxide, Carbon Dioxide, Sulfur Dioxide, Nitrogen Oxides and so on. The consumption of natural gas and primary energy is shown in Fig.5, natural gas covers the maximum percentage of the total energy consumption. The poisonous, odorless and colorless gas, Carbon Monoxide is emitted from vehicles resulting from improper combustion.
Generating electricity in power plants has a role in polluting air as mechanical power is acquired from the burning of fossil fuels to produce electrical power.
Each year, almost 3.8 million premature deaths are triggered by indoor air pollution and the vast majority of them is in the developing world . Burning of kerosene, wood, coal, and other fossil and biomass-based fuels produce Carbon Dioxide, Carbon Monoxide, polyaromatic hydrocarbons, Methane, volatile biological compounds, ash, smoke, which make breathing difficult, can stick to walls, food, clothing and contaminate air inside the house . Outdoor pollution is linked to power generation, industries, building heating systems, and vehicles. High PM10 level is one of the leading causes of respiratory diseases . Both the indoor and outdoor air pollution are responsible for deaths in Bangladesh which is shown in Fig.6.
In Bangladesh, Air Quality Standards have been set out for CO, Pb, NOX, SPM, PM10, PM2.5, O3 and SO2. In Dhaka, the concentration of Particulate Matter in the dry season has found to exceed NAAQS for more than 100 days of a year. . Continuous Air Quality Monitoring Stations (CAMS) represents that PM10 and PM2.5 are the most critical pollutants that generally exceed the National Ambient Air Quality Standard (NAAQS) during the dry season. Dhaka suffers air quality of below standard during particular days of this season, especially from November to March.
Greenhouse gases like Carbon Dioxide, Methane, nitrous oxide, and fluorinated gases are the catalysts of global warming. The concentration of these gases in the atmosphere, mainly Dioxide of Carbon, increases on average by 1% per year . Industries and factories release CFCs, Bromine, Chlorine which causes depletionof the Ozone layer, which protects of the earth from direct sunlight and Ultraviolet (UV) Rays and helps to filter the excess harmful radiation into it. Annual Greenhouse gas emission has been increased in a linear way from 2000 to 2012, which is shown in Fig.7.
Smoking releases Carbon Dioxide, Methane and other chemicals that cause air pollution. Annually around 2.6 billion kgs of Carbon Dioxide and 5.2 billion kgs of Methane are released globally . Tobacco smoke contains up to 40 carcinogens, a fatal form of air pollution . Tobacco farms also emit harmful gases from the machines used there by burning the fossil fuels. A nonsmoker can be the patient of respiratory diseases if he stays very close to a smoker for an extended period. Percentage of smokers in Bangladesh of different ages from 1990 to 2016 is shown in Fig.8.
Smoke can also be absorbed into bedding, carpet and furniture in a house leading to a variety of breathing and health concerns in the home .
Air conditioners can be a secondary reason of air pollution. There are a lot of refrigerant gases used to run refrigerators and air conditioners and some of them are CFC, HCFC, HFC and so on, some are responsible for the depletion of the Ozone layer. .
Natural events that pollute the air include volcanic eruptions, forest fires, wind erosion, evaporation of organic compounds, pollen dispersal, dust storms, and natural radioactivity, and many others.
By cutting down trees and firing wood in a large amount, the percentage of oxygen reduces and the Carbon Dioxide and Carbon Monoxide increases, eventually results in deforestation and global warming .
The minerals are extracted from the surface ground using large equipment releasing harmful substances in the air. Mercury is released from goldmines which can be the reason for lung cancer and Petroleum release a great portion of nitrous oxide and Carbon Dioxide. .
Open waste burning and organic waste in landfills release destructive dioxins, furans, Methane, and fine Particulate Matter (PM) like Black Carbon (BC) in the environment. Almost 40% of waste is openly burned all over the world.
Among the top 10 diseases which cause death in Bangladesh, it relates five to air pollution – lung cancer 13%, lower respiratory tract infections 7%, chronic obstructive pulmonary disease 7%, ischemic heart disease 6%, and stroke 5% . Both ambient and indoor air pollution alone causes about 21 percent of all deaths in Bangladesh, the highest among South Asian countries . Short-term effects like irritation of eyes, throat, or skin, allergies, coughing, sneezing, high fever, asthma, dizziness, conjunctivitis, fatigue, anxiety nausea, and headache can be seen due to dust pollution.
Dust mixed germs and metals cause diseases like lung cancer, asthma, bronchitis, dermatitis, pneumonia, tuberculosis, kidney damage, high blood pressure, nervous system damage, damage to reproductive organs, birth defects, etc. Irritating and bad smells in factories, garbage, sewer systems are also unpleasant. Skin cancers from Radon exposure, as well as secondhand and thirdhand smoke, vision problems, chronic obstructive pulmonary disease (COPD), abnormality in the mental development of the child are also seen.
Each year around 2.5 million people die globally due to air pollution. Young children, older adults, pregnant women, and the sick should avoid exposure to air pollution due to having a weaker immune system . Researchers declared relationship between the increase of polluting particles in cities and the thickening of the internal wall of the arteries or atherosclerosis . Some of them have found that long-term exposure to air pollution is associated with lower scores on tests of mental acuity as provokes modifications in brain structure that resemble those of Alzheimer’s disease. Again, PM 2.5 is associated with increased brain atrophy. 
Like other types of pollution such as water pollution and soil pollution, air pollution has also its negative consequence on environment.
Air pollution includes some microscopic particles and toxic pollutants which directly contaminate the water and soil surface damaging the sea animals, reduction in growing crops, demolition of young trees and other plants take place in great numbers, even force wildlife species to shift to a new place which disturbs the ecosystem, including photosynthesis.
The land pollution due to acid rain is a huge threat for maintaining the quality of the grown crops as it changes the soil composition; degrades water quality in rivers, lakes and streams; damages crops affecting food chains; and can cause buildings and monuments to decay .
A brief explanation of how the population, excessive vehicles in Dhaka, Brick kilns and other industries, and other sources are contributing major portion of polluting agents to the environment for the last couple of years is given in this paper. The explanation with the corresponding figures clearly shows that air pollution in Dhaka is increasing destructively every year. This is a great threat to the people of Dhaka city. This increasing air pollution results in various health effects and environment instability as well as damaged ecosystem.
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