Air pollution can be defined as any action natural or anthropogenic, which increases the concentration of air pollutants or introduce air pollutants in the atmosphere is known as air pollution, air pollutants are any solid, liquid or gaseous substance including noise present in the atmosphere in such concentration as may be or tend to be injurious to human beings or other living creatures or plants or property or environment.
Primary pollutants
The pollutants which are directly emitted from a known or identifiable source are known as primary pollutants which include gases like carbon monoxide, sulphur dioxide, hydrogen sulhpide, nitrogen oxide, ammonia, hydrocarbons and radioactive substances.
Secondary pollutants
Pollutants that are formed in the atmosphere due to chemical reactions among primary pollutants with normal atmospheric components such as ozone, nitrogen dioxide, sulphate, nitrates, sulphur trioxide,ketones and aldehydes etc the reasons for secondary pollutants are oxidation, dissociation and dissolution of primary pollutants.
Air can be polluted by natural causes like
· Eruption of volcanoes which emit gaseous pollutants like methane, sulphur dioxide, carbon dioxide, dust, ash etc,
· Forest fire which spews great amounts of carbon dioxide, carbon monoxide, ash smoke and soot.
· The dust storms also significantly add suspended particulate material in the atmosphere causing air pollution.
· Decomposition of organic matter under anaerobic conditions produces methane which on being oxidized in the atmosphere produces carbon monoxide. Decomposition of this matter also produces foul smelling gases.
· Gas emissions from the marshes and underground mines also increases the pollutant in the atmosphere
Following are the major anthropocentric activities causing air pollution
Transport: for transport we have developed so many different means like cars, buses, and trucks etc for road transport, ships and other sea vessels for waterways, airplanes and helicopters etc for air transport, majority of all them are powered by burning of fossil fuel which emit air pollutants in the atmosphere.
Power Generation : the consumption of electric power by any nation was considered as symbol of its economic development and most of the power is being generated by burning fossil fuel like coal ( bituminous and lignite), natural gas, naphtha or fuel oil like diesel etc. burning of these fossil fuels aggravate the problem of air pollution. Electricity production is the leading cause of industrial air pollution in the world, which comes in the forms of smog, soot, acid rain, mercury, particulate matter, and greenhouse gases like carbon dioxide. The Air pollution caused by power generation has drastic effects on human health, like bronchitis, asthma, emphysema, lung cancer, and cardiopulmonary disease etc.
During power generation Nitrogen oxide, sulfur dioxide, and particulate matter are released from the combustion of natural gas and coal. Nitrogen oxide reacts with sunlight to create ground level ozone and smog, which irritate the lungs and lower resistance to infections like the flu, causing significant respiratory problems per year.
Sulfur dioxide causes acid rain, and affects breathing, increases respiratory illness, and aggravates cardiovascular diseases. Particulate matter, or soot, affects the lungs and is particularly harmful to people with lung disease, like bronchitis or emphysema, and heart disease.
Coal-fired power plants also release mercury, a highly toxic metal that accumulates in the cells of fish and other animals that eventually get eaten by humans. Once consumed, mercury causes permanent damage to the liver and central nervous system; if consumed by pregnant women, it can also cause birth defects.
Nuclear energy, though lauded by some for emitting a relatively low amount of carbon dioxide and other airborne pollutants than other sources of energy, has its own set of health issues. When nuclear energy is produced and transported, there is always some amount (often a very small one) of danger of radiation and radioactive waste, which can cause cancer, sterility, immune system damage, miscarriages, genetic mutations, and death.
Finally, all of these energy sources emit greenhouse gases. Although the effects of global warming on individual health are indirect, they are significant. For example, a recent study done by Australian researchers found that during heat waves, hospital admissions increased by 7%; this does not bode well for a warmer future. More concretely, many different scientific reports have predicted that tropical and mosquito-borne diseases, such as malaria and dengue fever, will become more prevalent as global warming increases.
Indoor air pollution
Although seems very insignificant for a layman but indoor air pollution is one of the major causes of problems related to air pollution. Indoor air pollution refers to the physical, chemical, and biological characteristics of air in the indoor environment within a home, building, or an institution or commercial facility. Specially in the developed countries, where energy efficiency improvements sometimes make houses relatively airtight, reducing ventilation and raising pollutant levels. Indoor air problems can be subtle and do not always produce easily recognized impacts on health. Different conditions are responsible for indoor air pollution in the rural areas and the urban areas.
In the developing countries, it is the rural areas that face the greatest threat from indoor pollution, where some 3.5 billion people continue to rely on traditional fuels such as firewood, charcoal, and cow dung for cooking and heating. Concentrations of indoor pollutants in households that burn traditional fuels are alarming. Burning such fuels produces large amount of smoke and other air pollutants in the confined space of the home, resulting in high exposure. Women and children are the groups most vulnerable as they spend more time indoors and are exposed to the smoke. In 1992, the World Bank designated indoor air pollution in the developing countries as one of the four most critical global environmental problems. Daily averages of pollutant level emitted indoors often exceed current WHO guidelines and acceptable levels. Although many hundreds of separate chemical agents have been identified in the smoke from biofuels, the four most serious pollutants are particulates, carbon monoxide, polycyclic organic matter, and formaldehyde. Unfortunately, little monitoring has been done in rural and poor urban indoor environments in a manner that is statistically rigorous.
In urban areas, exposure to indoor air pollution has increased due to a variety of reasons, including the construction of more tightly sealed buildings, reduced ventilation, the use of synthetic materials for building and furnishing and the use of chemical products, pesticides, and household care products. Indoor air pollution can begin within the building or be drawn in from outdoors. Other than nitrogen dioxide, carbon monoxide, and lead, there are a number of other pollutants that affect the air quality in an enclosed space.
| National Ambient Air Quality Standards |
| POLLUTANTS | AVERAGE TIME | CONCENTRATION |
| Sulphur dioxide (SO2) | Annual average | 60 µg/m3 |
| | 24 hour | 80 µg/m3 |
| | | |
| Oxides of Nitrogen (NO2) | A.A | 60 µg /m3 |
| | 24H | 80 µg /m3 |
| | | |
| Suspended Particulate Matter (SPM) | A.A | 140 µg/m3 |
| | 24H | 200 µg/m3 |
| | | |
| Lead | A.A | 0.75 µg/m3 |
| | 24H | 1.0 µg/m3 |
| | | |
| Carbon Monoxide | A.A | 2.0 µg/m3 |
| | 24H | 4.0 µg/m3 |
| | | |
| Respirable Particulate Matter (RPM) | A.A | 60 µg/m3 |
| | 24H | 100 µg/m3 |
| | | |
Major air pollutants
Carbon monoxide (CO)is a colourless, odourless,tasteless and toxic gas produced by the incomplete burning of carbon-based fuels including petrol, diesel, and wood. It is also produced from the combustion of natural and synthetic products such as cigarettes.
Ill Effect of carbon monoxide
When Carbon monoxide is inhaled it combines with the oxygen carrying hemoglobin of the blood to form carboxyhemoglobin (COHb).and inhibits the blood's ability to carry oxygen to body tissues including vital organs such as the heart and brain. This severely reduces the supply of oxygen to the vital organs and may result in death in extreme cases. The symptoms include mild headache, nausea, unconsciousness and eventually death.
Carbon dioxide (CO2) carbon dioxide is a colorless and odorless gas produced when fossil fuel and biomass is burnt it is the principle greenhouse gas emitted as a result of human activities such as the burning of coal, oil, wood and natural gas etc. With increasing concentration of carbon dioxide the major problem is the global warming i.e. Increase in the average temperature of the earth resulting in to climate change. The topic of green house effect and its aftermaths is being already discussed in unit- II of the SSM. Because of the anthropocentric activities, the amount of CO2 released into the atmosphere has been rising extensively during the last 150 years.
There has been a climb in carbon dioxide concentrations in the atmosphere of about 280 ppm in 1850 to around 400 ppm in 2009 the major cause of n increasing the amount of carbon dioxide in air by burning of fossil fuels, by producing cement and by carrying out land clearing and forest combustion. About 22% of the current atmospheric CO2 concentrations exist due to these human activities, considered that there is no change in natural amounts of carbon dioxide
Chloroflorocarbons (CFC) are gases used as foaming, refrigerant and aerosol agent and when released into the air, CFCs rise to the stratosphere, where they come in contact with few other gases, which leads to a reduction of the ozone layer that protects the earth from the harmful ultraviolet rays of the sun. the topic of CFC an ODS ( ozone depleting substance) is discussed at length in the UNIT –IV of this SSM.
Lead is present in petrol, diesel as an additive it is used as an anti knocking agent which helps in reducing the noise produced by the vehicle, lead is also used in Lead acid batteries, paints and glues, hair dye products, rolled and extruded products, cable sheathing, shot and ammunition etc. the effect of lead humans depends on the concentrations and exposure of it, as compared to adult the children are more vulnerable to the effects of lead. High level lead in human body can result in problems in synthesis of hemoglobin, failure of kidney, problems in gastrointestinal tract, joints and reproductive system, and finally it also effects the central nervous system. Apart from the above mentioned effects small quantities of lead in children can lead to impairment of mental growth of children. Although we can intake lead from water, air and food, but the suspended lead in the air is one of the major causes of lead intake in our body.
Ozone occurs naturally in the upper layers of the atmosphere. This important gas shields the earth from the harmful ultraviolet rays of the sun. However, at the ground level, it is a pollutant with highly toxic effects. Ozone near lower levels of earth is highly toxic gas and is a pollutant of air. On ground ozone is formed at high temperature, where chemicals emitted from industrial processes, vehicle exhaust, and other products of fossil fuel combustion and initiate a complex series of reaction which result in the formation of ozone. As concentrations of these pollutants involved in ozone formation (precursors of ozone) increase with industrialization and vehicle traffic, ozone concentrations increase at ground level where we breathe.
When ozone is inhaled it reacts with molecules in the lining of our airways and lungs and chemical bonds break and reform in different ways with the addition of oxygen atoms (the process of oxidation) from ozone, and this cause acute inflammation. This weakens the ability of the lining of our airways to provide a protective barrier to microbes, toxic chemicals, and allergens. In reaction to it our airways respond by covering the affected areas with fluid and by contracting muscles. This results in to shortness of breath, dry cough or pain when taking a deep breath, tightness of the chest, wheezing, and sometimes even nausea are common responses to ozone. Breathing becomes more difficult.
The acute effects of short-term exposure to ozone are reversible; but human body’s response to long-term exposure may not be reversible. Ozone also triggers asthma and may aggravate other respiratory illnesses such as pneumonia and bronchitis. Ozone concentrations can make the small bands of muscles that help control breathing more sensitive to dry air, cold or dust, so ozone exposure may increase allergic responses in susceptible people. Ozone is also responsible for weakening of resistance power or immunity of humans and make us more susceptible to other diseases.
Nitrogen oxide (Nox) is produced when nitrogen reacts with oxygen at high temperature and pressure factories, motor vehicles and power plants that burn fossil fuels produce nitrogen oxides are the major sources of Nitrogen oxide( NOx) production . in comparison diesel engines produce a disproportionately large amount of NOx when compared to gasoline engines because of their high temperature combustion process. These are green house gases that contribute to the global warming of the earth. The environmental effects of nitrogen oxides include formation of smog, reduction of visibility, act as catalyst in formation of ground level ozone, leads to oxygen depletion in water bodies and upsets chemical balance of aquatic wildlife, contribute in the formation of acid in the atmosphere causing acid rain etc which also leads to acidification of water resources like lakes and stream etc it is also related to biological mutations as well. The effects of humans include respiratory problems such as asthma, emphysema and bronchitis, can damage lung tissues, aggravates cardiac diseases and can also become the cause of premature death.
Suspended particulate matter (SPM) are the solid substances which can remain suspended in the air, in the form of dust, smoke and vapour mixture, for extended periods and is also the main source of haze which reduces visibility. These particles, when breathed in can accumulate in our lungs and cause lung damage and respiratory problems. A similar substance known as Particulate matter or PM consists of soot and dust particles that are smaller than the diameter of a human hair. There are two classifications for particulate matter. The suspended particles, smaller than 10 microns in diameter are classified as PM10 or coarse size particles. The fine size particles, of size less than or equal to 2.5 microns in diameter is classified as PM 2.5. Sources of PM include diesel exhaust, soil dust, tire wear, and soot. These particles penetrate deeply into the lungs and are captured by lung tissue. A major contributor to the PM pollution problem is exhaust from diesel vehicles, which produce 79% of the particulate emissions from mobile sources. The most dangerous aspect of PM pollution from diesel vehicles is the hundreds of different chemicals that are adsorbed to the particle. Exposure to PM pollution has been associated with respiratory and cardiac problems, infections, asthma attacks, lung cancer and decreased life expectancy. According to one estimate of World Health Organization it has been stated that 500,000 premature deaths each year may be associated with PM pollution. Fine particulate air pollution (<2.5 microns) is thought to be more dangerous because of its ability to penetrate deeper into lung tissue. A recent study found that even a small increase in PM2.5 can result in a significant increase in mortality. In fact, The American Lung Association believes that PM2.5 represents the most serious threat to our health. Segments of the population that are more susceptible to PM pollution include children, athletes, senior citizens, and people with pre-existing respiratory problems.
Sulfur dioxide is a colorless, highly reactive gas; it is majorly produced by power plants, motor vehicles, refineries that burn fossil fuels. It is also produced from manufacturing of paper and smelting of metals. Fossil fuels like coal and oil vary in sulfur concentrations and as a result the amount of sulfur dioxide they produce when burned. A high level of sulfur dioxide in exhaust gas can interfere with emission control mechanisms for other pollutants, as presence of sulphur dioxide helps in formation of other pollutants like nitrogen oxide, ozone etc. SOx can react with other compounds in the atmosphere to form small particles. These particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory diseases like emphysema and bronchitis, and can aggravate existing cardiac disease, leading to increased hospital admissions and premature death. Sulfur dioxide also reduces respiratory volume, and increases breathing resistance in those exposed, especially asthmatics. Studies have also shown that sulfur dioxide increases nasal airway resistance. Sulphur dioxide also contribute in the formation of acid rain and smog.
Hydrocarbons are a class of reactive organic gases or ROG, which are formed solely of hydrogen and carbon chain. The emission of Hydrocarbon gases results from the incomplete burning of any organic matter such as oil, wood, or rubber. Emissions from generators, vehicles etc, exhausts from oil refineries, and oil-fueled power plants are the primary sources of hydrocarbons. The evaporation from petroleum products, solvents, dry cleaning solution, paints and dyes etc while distribution or use also contribute to the hydrocarbon in the atmosphere.
The environmental impact of hydrocarbons includes the formation of ozone and the resulting smog problem. Carcinogenic forms of hydrocarbons are considered hazardous air pollutants, or air toxics. The primary health effect of hydrocarbons results from the formation of ozone and its related health effects. High levels of hydrocarbons in the atmosphere can interfere with oxygen intake by reducing the amount of available oxygen through displacement.
Air Toxics
Benzene, formaldehyde, acetaldehyde, 1,3-butadiene, and acrolein are typical examples of air toxics, air toxics are known as hazardous air pollutants, more than 180 toxic and potentially toxic compounds are termed as air toxics.
Air toxics are generally organic chemicals, including some hydrocarbons that are highly evaporative in nature. Vehicular emissions, chemical manufacturing units, paint and dye industries, and other operation that uses organic compounds are the major source of air toxic.
Air toxics are pollutants that cause or are suspected as carcinogenic substance causing cancer. Cancer is the primary health effect studied due to the low exposure concentrations of these air toxics such as benzene and formaldehyde. Benzene has been shown to cause aplastic anemia and acute myelogenous leukemia in occupational studies of workers exposed to it. Known health concerns related to aldehydes include cancer, asthma, and respiratory tract irritation. It is also believed that these air toxics have impacts on the reproductive system by causing chromosomal aberrations or mutations. The nature of air toxics still poses many uncertainties about their true health effects. These chemical compounds have many different forms and metabolites as they are broken down, and little is known about how they interact with the body. The health effects of particulate matter from diesel exhaust are thought to be attributable to the many air toxics that are adsorbed to the particles. These small particles penetrate deeply into the lungs, and are the perfect vehicle for delivering air toxics into the body.
Some environmental problems created by air pollution
Acid rain
When sulphur dioxide and nitrogen oxides in the air combine with water vapour in the atmosphere they react to form sulfuric acid and nitric acid, it is mixed with the rain, snow or fog and fall on earth is known as acid rain or acid desposition. Acid rain causes extensive damage to water resources, forest, soil resources and other living creatures on the earth. Due to increase in acidity in water resources many species has disappeared from some parts of the world, like USA, Europe etc. Acid rains are also corrosive in nature and can damage buildings and other such construction, the best example is the yellowing of Taj Mahal due to Mathura refinery in India. When acid rain is absorbed by soil the soil is acidified, tree roots are damaged, leaving them not able to draw in enough nutrients to support the tree. When acid rain falls on trees, it makes their leaves turn brownish-yellow and the tree can no longer carry out photosynthesis properly. Another problem is it will harm people when they breathe in smog, acid rain in one of its many forms. Acid rain can also harm people indirectly. This happens when people eat fish caught in affected lakes or rivers. Also, if the water source is acidic enough, it will react with copper or lead pipes to harm humans. It also washes aluminum into the water supply. Birds can be harmed if they live in affected waters or feed on fish living in affected waters
Smog
Smog is the product of secondary air pollution, when the pollutants like nitrogen oxide, sulfur dioxide, hydro carbons, smoke and soot etc mix with the water vapour and dust and react in the presence of sunlight and heat it forms particulate matters which result in the formation of dense and hazy gaseous cover known as smog, the word smog is the combination of smoke and fog, the term was first used in 1905 by Dr H A Des Voeux to describe the conditions of fog that had soot or smoke in it.
Smog is usually formed when the temperature is low and wind is calm, due to slow speed of wind and low temperature the gaseus emissions are not able to move up and remain at relatively low levels near the ground, the fog and these gases combine together to form smog, which has various effects like the following,
It hampers visibility of the area causing disruption of road, rail and air traffic. Heavy smog also decreases ultraviolet radiation reaching earth leading to decrease in formation of vitamin D in body. The most harmful components of smog are ground-level ozone and fine airborne particles. Ground-level ozone forms when pollutants released from gasoline and diesel-powered vehicles and oil-based solvents react with heat and sunlight. It is harmful to humans, animals, and plants. Smog can irritate and inflame pulmonary membranes, causing chest pains, coughing, and throat irritation. Other illnesses such as colds and pneumonia can also be brought on by exposure to smog. Prolonged exposure to smog may result in to respiratory problems and ultimately death. The first smog-related deaths were recorded in London in 1873, when it killed 500 people. In 1880, the toll was 2000.
The origin of formation of smog can be traced to the industrial revolution of the 19th century when the industries and the households relied heavily on coal for heating and cooking. Due to the burning of coal for heat during the winter months, emissions of smoke and sulphur dioxide were much greater in urban areas than they were during the summer months. Smoke particles trapped in the fog gave it a yellow/black color and this smog often settled over cities for many days.
Flyash
The burning of coal for various purpose, chiefly for power generation result in to formation of residual ash known as fly ash due to its light nature and small particulate structure, fly ash consists of silica, alumina, oxides of iron, calcium and magnesium and traces of toxic heavy metals like lead, arsenic, cobalt and copper. When fly ash is disposed in the waste land it is blown away with air where it remains suspended and cause air pollution, to prevent this water is sprinkled on the disposal sites.
Fly ash being very minute tends to remain airborne for a very long period leading to serious health problems as the airborne ash can enters the human body. The effects include irritation to eyes, skin, and nose, throat, and respiratory tract. Repeated inhalation of fly ash dust containing crystalline silica can cause bronchitis and lung cancer.
Volatile organic compounds originate mainly from solvents and chemicals. The main indoor sources are perfumes, hair sprays, furniture polish, glues, air fresheners, moth repellents, wood preservatives, and many other products used in the house. 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.
Tobacco smoke generates a wide range of harmful chemicals and is known to cause cancer. 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.
Pesticides , if used carefully and the manufacturers, instructions followed carefully they do not cause too much harm to the indoor air.
Biological pollutants include pollen from plants, mite, hair from pets, fungi, parasites, and some bacteria. Most of them are allergens and can cause asthma, hay fever, and other allergic diseases.
Formaldehyde is a gas that comes mainly from carpets, particle boards, and insulation foam. It causes irritation to the eyes and nose and may cause allergies in some people.
Asbestos is mainly a concern because it is suspected to cause cancer.
Radon is a gas that is emitted naturally by the soil. Due to modern houses having poor ventilation, it is confined inside the house causing harm to the dwellers.
| Common atmospheric pollution sources and their pollutants |
| Category | Source | Emitting pollutants |
| Agriculture | Open burning | Suspended particulate matter, carbon monoxide, volatile organic compounds |
| Mining and quarrying | Coal mining; crude oil and gas production; stone quarrying | Suspended particulate matter, sulphur dioxide, oxides of nitrogen, volatile organic compounds |
| Power generation | Electricity; gas; steam | Suspended particulate matter, sulphur dioxide, oxides of nitrogen, carbon monoxide, volatile organic compounds, sulphur trioxide, lead |
| Transport | Combustion engines | Suspended particulate matter, sulphur dioxide, oxides of nitrogen, carbon monoxide, volatile organic compounds, lead |
| Community service | Municipal incinerators | Suspended particulate matter, sulphur dioxide, oxides of nitrogen, carbon monoxide, volatile organic compounds, lead |
