what is Air Pollution
According to WHO, air pollution is defined as the presence of materials in the air that are harmful to humans and their environment.
Causes and Sources of Air Pollution
Air pollution is caused by various types of pollutants released mainly from industries, thermal power plants, domestic appliances, and automobiles.
Petroleum refineries release poisonous gases like sulphur dioxide (SO2), nitrogen oxides (NO) etc. Dust is produced from cement factories as stone crushers and hot mix plants release suspended particulate matter (SPM) more than five times the safety limits by industrial standards. The thermal power plants produce deadly pollutants such as fly ash, SO2,, hydrocarbons etc. Other industries like food, fertilisers and chemical manufacturing plants also produce harmful poisonous gases.
In urban areas, automobiles are the chief sources of pollution. The ever-increasing traffic density has aggravated the existing problem of air pollution particularly in the major cities of the world. Automobiles mainly produce pollutants like unburnt hydrocarbons, CO, NO,, lead oxides, etc. Other pollutants like aldehydes, esters, ethers, ketones, and peroxides are also found in automobile emissions.
Aircraft emits carbon dioxide, water vapour, nitrogen oxide, and other substances that could be polluting. Jet aircrafts are estimated to produce 2 to 3 per cent of NOx emissions, but constitute the only source of high-level NOx (which may be implicated in global warming and ozone depletion). Aircraft also produce high-level water vapour, which forms ice particles that reflect heat back to earth, adding to the greenhouse effect. Air transport constitutes 2 to 3 per cent of carbon dioxide emissions produced by the use of fossil fuels. Carbon monoxide emissions from aircraft have decreased over time, however.
The chief pollutants derived from different sources are listed below:
Complete combustion of fossil fuels like mineral oil and coal produces Co, and Co. The major portion of CO, in the atmosphere is derived from the burning of fuels in power plants, industries, domestic cooking, heating, etc.
The principal sources of Co, apart from automobiles, are combustion processes such as stoves, forest fires and open fires.
Fossil fuels like coal release sulphur compounds like SO2, hydrogen sulphide (H2,S) and sulphuric acid (H2,SO4). Amongst all the compounds, the oxides of sulphur are considered to be the most poisonous pollutants. The other compounds include carbonyl sulphide (Cos), carbon disulphide (CS), dimethyl sulphide [(CH),S), and sulphates (XSO).
Nitrogen oxides (NO)
Nitrogen monoxide (NO), nitric acid (HNO3) and nitrogen dioxide (NO) are released by automobiles, industries, power plants etc. NO is the chief pollutant produced naturally as a result of combustion of oxygen and nitrogen at the time of lightning discharges and also due to bacterial oxidation of ammonia (NH), a variety of nucleophile molecule.
NO leads to the formation of several secondary pollutants like PAN, ozone (O3), carbonyl compounds, etc.
It is released from home appliances like refrigerators, air conditioners etc. in the process of the release of harmful chlorofluorocarbons (CFCs). O, is also formed in the atmosphere as a result of chemical reactions involving pollutants like SO, NO,, aldehydes, etc.
Fluorocarbons– These pollutants are released from industries, insecticides, etc.
Hydrocarbons – These are released mainly by automobiles and industries. The chief varieties are benzene and methane.
These pollutants are found in solid, liquid, and gaseous forms. Metals such as lead, nickel, arsenic, beryllium, tin, vanadium, titanium, and cadmium are released as pollutants by automobiles, metallurgical processes, etc.
Automobiles mostly release these to create photochemical smog. In the presence of solar rays, NO, O,, and hydrocarbons react with each other and are transformed into secondary pollutants which are toxic in nature.
Power plants, stone crushers in industries, etc. release fly ash, dust, and grit as suspended matter. Suspended particulate matter (SPM) like fine dust particles and soot emitted by industrial units. Biological particulate pollutants such as bacterial cells, fungal spores, and pollens are also found in the air.
(heavy metals excluded) These complex chemical substances are released by industries
Scientists have brought out the health hazards caused by dioxin, a toxic chemical that is released into the environment mainly through combustion process. Dioxins were first discovered in the flue gas and flyash of municipal waste incinerators in 1977. Since then, it has been shown worldwide that all municipal and hospital waste incinerators produce dioxins. The term dioxin refers to a class of chlorinated tricyclic ethers that exhibit similar physical and chemical characteristics.
The emissions from incinerators include carbon dioxide, water vapour and particulate matter in the form of fly ash and bottom ash, and process water. Fly and bottom ash contain a number of organic compounds which include polychlorinated aromatic compounds (PAC) such as dioxin and furans. This is due to inefficient combustion of volatile matter, varying contents of chlorinated plastic materials, and the lack of gascleaning systems of small combustion units. Since it is soluble in fat, dioxin invades the food chain and is mainly found (97.5 per cent) in meat, fish and dairy products.
Impact of Co,), it also causes global by contributing to the greenhouse effect. Unde normal conditions, the energy balance is maintained in the earth’s atmosphere as the solar heat received by the earth gets radiated back to space. But the concentration of CO2, in the atmosphere prevents heat from escaping. As a result, atmospheric temperature increases. It is called the greenhouse effect because the thick layers of CO2, act as glas blankets of a greenhouse which allow solar ray to penetrate but prevent the solar heat from escaping
Some scientists think that global warming caused by Co, emission may lead to a rise in global mean temperature even up to 4.5°C by the year 2050. This may cause the melting of polar ice caps and a rise in sea level. So, vast sections of coastal areas and islands may be submerged causing displacement of people and a tremendous loss of property. It is also being predicted that the increasing global temperature may accelerate the rate of evaporation from the earth’s surface, and this may adversely affect crop yield.
CO is poisonous when it reaches a level of 100 parts per million (ppm). It causes breathing problems, headache, irritation of the mucous membranes, etc. If the concentration of this gas reaches 1000 ppm, it causes loss of consciousness within an hour and death within four hours. If CO2 is inhaled for a few hours at a concentration of 200 ppm, it combines with blood haemoglobin and forms carboxyhaemoglobin leading to a decrease in the oxygen-carrying capacity of blood-the condition is called hypoxia.
Even the plants are affected by higher concentration of CO2 (100 to 10,000 ppm): they suffer excess shedding of leaves, leaf curling, reduction in the size of leaves, premature ageing, etc.
SO2, and hydrogen sulphide (H2,S) are the major pollutants among sulphur compounds. SO2, is released by the burning of coal in smelting industries and thermal power plants. Exposure to SO2, causes problems like irritation of eyes and swelling of the respiratory tract. In most plants, SO2, causes bleaching of leaf pigments.
Hydrogen Sulphide (H2,S) when concentrated in low amounts produces nausea, headache, collapse, even coma and death. Conjunctivitis and
The concentration of Co, in the atmosphere accelerates the rate of photosynthesis in plants. Thus tree growth, particularly in equatorial regions, increases. Studies reveal that the rate of tree growth in the Amazon river basin in South America has increased during the past 100 years due to greater supply of CO, in the atmosphere. Although CO2, acts as a fertiliser (due to rapid growth of trees and their decomposition in the
Irrigation Nucous membranes produced when H2, S concentration is around 150 ppm. Colic diarrhoea and bronchial pneumonia are produced when people are exposed for 15 to 30 minutes to around 500 ppm concentration of H,S.
Nitrogen Oxides include nitrous oxide, nitrogen oxide, nitric oxide, etc. (Nitrous oxide has world average level of about 0.25 ppm. The gas does not cause any serious hazard at such low levels.)
to 0.5 Nitrogen dioxide (N2O) is the prime constituent of photochemical smog in urban areas. It causes diseases like irritation of the alveoli in the lungs if a person has prolonged exposure to 1 ppm level. It may be followed by edema and death. It causes retarded growth in the case of plants if plants are exposed to 0.3 ppm ppm for 10 to 20 days. Exposure to 4 ppm to 8 ppm for 1 to 4 hours may cause leaf injury in plants.
Ozone is beneficial due to two factors. One, it absorbs ultraviolet (UV) rays; thus UV rays are prevented from reaching the earth’s surface. Two, by absorbing UV rays the stratosphere is heated up causing an inversion of temperature; as an immediate effect of this phenomenon the vertical mixing of pollutants in urban industrialised areas is restricted and the pollutants start spreading horizontally in low altitudes. However, as a result of 0, concentration near the earth’s surface, the health of living animals is seriously affected. In the case of plants, leaves are damaged. At 0.02 ppm concentration, 0, may cause damage to tobacco, tomato, bean and grape plants. Ozone at ground level is part of smog and can irritate our eyes.
Although fluorides can prevent tooth-decay at low levels, these are toxic when they reach higher levels. Fluorides are released from phosphate fertilisers, ceramics, fluorinated plastics, fluorinated hydrocarbons, etc. In plants fluorides cause tip burn of leaves. Hydrocarbons have a high carcinogenic effect on lungs, and they also cause irritation to the eye. nose and throat.
Among metals, mercury causes damage to the nervous system, liver and eyes. Symptoms like headache, fatigue, anxiety and loss of appetite are seen if a person suffers mercury contamination Long contact with or inhalation of lead dus may cause anaemia and damage to liver and kidneys.
Photochemical products such as olefins cause the removal of sepals in orchids and shedding of petals in carnations. Aldehydes cause irritation of skin, eyes and upper part of the respiratory tract. Benzpyrene causes cancer whereas PAN causes eye irritation. Petrochemical smog may lead to emphysema, which involves a breakdown of the alveoli in the lungs.
Common diseases caused by particulate matter are tuberculosis and cancer. Dust of cotton produces a respiratory disease called byssinosis. Asbestos dust causes lung diseases, lead causes nervous disorders and brain damage.
Toxicants like arsenic, asbestos, chromium, nitrosamines cause cancer. Chloroform and carbon tetrachloride produce cancer in rats, mice and other animals. Vinyl chloride is suspected to produce brain and lung cancers. Chemicals like organochlorine pesticides, Polychlorinated biphenyls (PCBs) and dioxins act as weak oestrogens and may cause breast cancer. These chemicals, known as ‘gender benders’, reduce male sperm count, and they call for immediate attention since they are toxic in even minute quantities. The inhalation of high amounts of dioxin not only chokes the lungs but also permits its entry into the blood stream. The liver becomes directly affected, leading to increased susceptibility to cancer.
Indoor Air Pollution
The indoor environment provides an intimate field of action for a host of airborne pollutants, from the exotic chemical effluents of modern technology to the more traditional by-products of smoking, cooking, and heating. The health risks of indoor air pollution are magnified because people the world over spend 80-90 per cent of their time indoors.
Seven million people die each year because of exposure to air pollution, as per figures put out by the World Health Organisation (WHO) for 2012. That makes air pollution the single greatest environmental health risk on earth. More than half of those deaths are caused by indoor pollutants, which in the developing world largely come from indoor cooking stove fuels like wood, coal, and cow dung. The WHO report measured the global.
Impact of pollution by region, not individual countries. The western Pacific, Southeast Asian and African regions accounted for almost six million premature deaths. But there have beer fewer than 400,000 premature deaths from ai pollution in high-income countries and regions o Europe and the Americas, where laws and regulations have decreased outdoor air pollution smoking indoors has become culturally unacceptable, and almost no one cooks with coa or cow dung.
Cooking and heating with solid fuels (wood charcoal, crop waste, dung, and coal) produce high levels of smoke in and around the home tha contains a variety of health-damaging pollutants There is strong evidence that exposure to household air pollution can lead to a wide range of child and adult disease outcomes, including acute and chronic respiratory conditions (e.g pneumonia, chronic obstructive pulmonary disease) lung cancer, ischemic heart disease, stroke and cataract. There is also supporting evidence suggesting exposure to household air pollution is linked with adverse pregnancy outcomes, tuberculosis, upper aero-digestive tract, cervical and other cancers.
There is substantial evidence that exposure to smoke from the use of solid fuels in the home increases the risk of acute lower respiratory infections (ALRI) in young children, particularly pneumonia. Exposure to household air pollution accounts for more than half of deaths to childhood pneumonia in children under five years of age.
Chronic obstructive pulmonary disease (COPD) is a progressive and incompletely reversible airflow obstruction. There is a substantial body of evidence showing that household air pollution is an important risk factor for such disease (and possibly the most important cause of COPD in non-smoking populations).
Smoke from both coal and biomass contains substantial amounts of carcinogens (chemical substances known to increase the risk of cancer) A consistent body of evidence shows that individuals exposed to smoke from biomass and coal fires in the home have an elevated risk of lung cancer.
Particulate matter is a health-damaging pollutant common to air pollution from different combustion sources including ambient air pollution, second-hand smoke and active smoking. Recent
sources estimate the risk and mortality for ischaemic heart disease and stroke. These estimates have been applied to similar combustion sources from household energy use, to generate mortality estimates of ischaemic heart disease and strokes from household indoor air pollution.
Cataract is the main cause of blindness of the adult population in developing countries. An increasing number of epidemiological studies and toxicological evidence provide good evidence that household solid fuel use for cooking is associated with cataract formation, especially among women.
Fire-related burns from fuel use in low and middle income homes are an important cause of death, especially among children. Deaths are only part of the problem–for every child and adult person who dies from burns, many more are left with lifelong disabilities and disfigurements. A high proportion of these burns and scalds results from the dangers posed to children and women by solid fuel and kerosene stoves which are often located at floor level in poorly lit kitchens increasing the safety risk.
Poisoning is another previously underestimated health risk, which is posed by the unintentional ingestion of kerosene, particularly among young children. In low and middle-income countries kerosene is commonly bought and stored in soft drink or milk bottles, which explains this health risk and the need to protect children from this hazard.
There is emerging evidence which suggests that household air pollution in developing countries may also increase the risk of other important child and adult health problems, although this evidence is tentative and based on fewer studies. It includes conditions such as: low birth weight and perinatal mortality (still births and deaths in the first week of life), asthma, otitis media (middle ear infection) and other acute upper respiratory infections, tuberculosis, nasopharyngeal cancer, laryngeal cancer, and cervical cancer.
The inefficient use of energy by households has impacts beyond health. The inefficient use of solid fuels for cooking and heating is a major source of short-lived climate pollutants (e.g., black carbon) and the unsustainable harvesting of fuelwood contributes to local forest degradation.
The collection of fuel imposes a serious time burden on women and children and alleviating this drudgery is important. solid fuels constitutes one of the indicators to monitor progress towards ensuring environmental sustainability
Indoor air pollution is a concern in the developed countries also, though due to other reasons. Energy efficiency improvements sometimes make houses relatively airtight, reducing ventilation and raising pollutant levels. Exposure to indoor air pollution has increased due to the use of synthetic materials for building and furnishing and the use of chemical products.
Cigarettes, for instance, are potent emitters of carbon monoxide (CO), aldehydes, and a variety of carcinogens. It is well known that passive smoking causes a wide range of problems to the passive smoker (the person who is in the same room with a smoker and is not himself/herself a smoker) ranging from burning eyes, nose, and throat irritation to cancer, bronchitis, severe asthma, and a decrease in lung function. Gas appliances and unvented kerosene heaters are a primary source of indoor nitrogen dioxide (NO), a respiratory irritant. Building materials such as particle board, plywood, and foam insulation give off formaldehyde, a probable carcinogen. Common consumer products that give off volatile organic compounds include dry-cleaned clothing, cleaning products, carpet adhesives, moth balls, and aerosol products. The main health effect is the imitation of the eye, nose and throat. In more severe cases there may be headaches, nausea and loss of coordination. In the long term, some of the pollutants are suspected to damage to the liver and other parts of the body. Finally molds, bacteria, fungi, asbestos, and radon are also known as airborne contaminants in the home and workplace. Most of them are allergens and can cause asthma, hay fever, and other allergic diseases.
Controlling Measures of Air Pollution
For checking industrial pollution it is necessary to remove particulate matter and gaseous pollutants from the industrial wastes. The removal of particulate matter is possible by using devices such as cyclone collectors which remove about 70 per cent of the particles and electrostatic precipitators (ESPs) which can remove the particles from gas by applying electrical forces within the precipitator’s chamber, and can effectively remove 99 per cent of the particulates.
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