Air Pollution, contamination of the atmosphere by gaseous, liquid, or solid wastes or by-products that can endanger human health and the health and welfare of plants and animals, or can attack materials, reduce visibility, or produce undesirable odours.
Air Pollutant : Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. They may be in the form of solid particles, liquid droplets, gases, or in combination thereof. Generally, they fall into two main groups: (1) those emitted directly from identifiable sources and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation. Exclusive of pollen, fog, and dust, which are of natural origin, about 100 contaminants have been identified and fall into the following categories: solids, sulfur compounds, volatile organic chemicals (VOC), nitrogen compounds, oxygen compounds, halogen compounds, radioactive compounds, and odors.
Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory disease. While major stationary sources are often identified with air pollution, the greatest source of emissions is actually mobile sources, mainly automobiles. Gases such as carbon dioxide, which contribute to global warming, have recently gained recognition as pollutants by some scientists. Others recognize the gas as being essential to life, and therefore incapable of being classed as a pollutant.
Pollutants
There are many substances in the air which may impair the health of plants and animals (including humans), or reduce visibility. These arise both from natural processes and human activity. Substances not naturally found in the air or at greater concentrations or in different locations from usual are referred to as 'pollutants'.
Pollutants can be classified as either primary or secondary.
Primary pollutants are substances directly produced by a process, such as ash from a volcanic eruption or the carbon monoxide gas from a motor vehicle exhaust.
Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone - one of the many secondary pollutants that make up photochemical smog.
Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include:
Sulfur oxides (SOx) especially sulfur dioxide, Nitrogen oxides (NOx) especially nitrogen dioxide, Carbon monoxide (CO), Carbon dioxide (CO2), a greenhouse gas.
Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.
Particulate matter (PM), such as smoke and dust. PM10 is used to describe suspended particles 10 microns in diameter and smaller, and PM2.5 has a maximum particle size of 2.5 microns.
Metal oxides, especially those of lead, and to a lesser degree cadmium, copper, and iron
Chlorofluorocarbons (CFCs), harmful to the ozone layer.
Ammonia (NH3) , Odors, such as from garbage, sewage, and industrial processes.
Secondary pollutants include:
Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog, such as nitrogen dioxide, Ground level ozone (O3), Peroxyacetyl nitrate (PAN)
Anthropogenic sources (human activity) related to burning different kinds of fuel
"Stationary Sources" as smoke stacks of power plants, manufacturing facilities, municipal waste incinerators
"Mobile Sources" as motor vehicles, aircraft etc., Combustion-fired power plants
Controlled burn practices used in agriculture and forestry management, Motor vehicles generating air pollution emissions, Marine vessels, such as container ships or cruise ships, and related port air pollution, Burning wood, fireplaces, stoves, furnaces and incinerators
Other anthropogenic sources
Oil refining, power plant operation and industrial activity in general, Chemicals, dust and crop waste burning in farming, (see Dust Bowl), Fumes from paint, hair spray, varnish, aerosol sprays and other solvents, Waste deposition in landfills, which generate methane.
Military uses, such as nuclear weapons, toxic gases, germ warfare and rocketry.
Natural sources
Dust from natural sources, usually large areas of land with little or no vegetation.
Methane, emitted by the digestion of food by animals, for example cattle.
Radon gas from radioactive decay within the Earth's crust.
Smoke and carbon monoxide from wildfires.
Volcanic activity, which produce sulfur, chlorine, and ash particulates.
Pollutants
A substance in the air that can be adverse to humans and the environment is known as an air pollutant. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made. Pollutants can be classified as primary or secondary. Usually, primary pollutants are directly produced from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone — one of the many secondary pollutants that make up photochemical smog. Some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include:
Sulfur oxides (SOx) - especially sulfur dioxide, a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
Nitrogen oxides (NOx) - especially nitrogen dioxide are expelled from high temperature combustion, and are also produced naturally during thunderstorms by electric discharge. Can be seen as the brown haze dome above or plume downwind of cities. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants.
Carbon monoxide (CO)- is a colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
Volatile organic compounds - VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is another dangerous compound which is often associated with industrial uses.
Particulates, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulates can be man made or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.
Persistent free radicals connected to airborne fine particles could cause cardiopulmonary disease.
Toxic metals, such as lead and mercury, especially their compounds.
Chlorofluorocarbons (CFCs) - harmful to the ozone layer emitted from products currently banned from use.
Ammonia (NH3) - emitted from agricultural processes. Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.
Odors — such as from garbage, sewage, and industrial processes
Radioactive pollutants - produced by nuclear explosions, nuclear events, war explosives, and natural processes such as the radioactive decay of radon.
Secondary pollutants include:
Particulates created from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
Ground level ozone (O3) formed from NOx and VOCs. Ozone (O3) is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant, and a constituent of smog.
Peroxyacetyl nitrate (PAN) - similarly formed from NOx and VOCs.
Minor air pollutants include:
A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive
A variety of persistent organic pollutants, which can attach to particulates
Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment.
Major air pollutants and their associated health hazards
Air Pollutant : Any substance in air that could, in high enough concentration, harm man, other animals, vegetation, or material. Pollutants may include almost any natural or artificial composition of airborne matter capable of being airborne. They may be in the form of solid particles, liquid droplets, gases, or in combination thereof. Generally, they fall into two main groups: (1) those emitted directly from identifiable sources and (2) those produced in the air by interaction between two or more primary pollutants, or by reaction with normal atmospheric constituents, with or without photoactivation. Exclusive of pollen, fog, and dust, which are of natural origin, about 100 contaminants have been identified and fall into the following categories: solids, sulfur compounds, volatile organic chemicals (VOC), nitrogen compounds, oxygen compounds, halogen compounds, radioactive compounds, and odors.
Worldwide air pollution is responsible for large numbers of deaths and cases of respiratory disease. While major stationary sources are often identified with air pollution, the greatest source of emissions is actually mobile sources, mainly automobiles. Gases such as carbon dioxide, which contribute to global warming, have recently gained recognition as pollutants by some scientists. Others recognize the gas as being essential to life, and therefore incapable of being classed as a pollutant.
Pollutants
There are many substances in the air which may impair the health of plants and animals (including humans), or reduce visibility. These arise both from natural processes and human activity. Substances not naturally found in the air or at greater concentrations or in different locations from usual are referred to as 'pollutants'.
Pollutants can be classified as either primary or secondary.
Primary pollutants are substances directly produced by a process, such as ash from a volcanic eruption or the carbon monoxide gas from a motor vehicle exhaust.
Secondary pollutants are not emitted. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone - one of the many secondary pollutants that make up photochemical smog.
Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include:
Sulfur oxides (SOx) especially sulfur dioxide, Nitrogen oxides (NOx) especially nitrogen dioxide, Carbon monoxide (CO), Carbon dioxide (CO2), a greenhouse gas.
Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.
Particulate matter (PM), such as smoke and dust. PM10 is used to describe suspended particles 10 microns in diameter and smaller, and PM2.5 has a maximum particle size of 2.5 microns.
Metal oxides, especially those of lead, and to a lesser degree cadmium, copper, and iron
Chlorofluorocarbons (CFCs), harmful to the ozone layer.
Ammonia (NH3) , Odors, such as from garbage, sewage, and industrial processes.
Secondary pollutants include:
Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog, such as nitrogen dioxide, Ground level ozone (O3), Peroxyacetyl nitrate (PAN)
Anthropogenic sources (human activity) related to burning different kinds of fuel
"Stationary Sources" as smoke stacks of power plants, manufacturing facilities, municipal waste incinerators
"Mobile Sources" as motor vehicles, aircraft etc., Combustion-fired power plants
Controlled burn practices used in agriculture and forestry management, Motor vehicles generating air pollution emissions, Marine vessels, such as container ships or cruise ships, and related port air pollution, Burning wood, fireplaces, stoves, furnaces and incinerators
Other anthropogenic sources
Oil refining, power plant operation and industrial activity in general, Chemicals, dust and crop waste burning in farming, (see Dust Bowl), Fumes from paint, hair spray, varnish, aerosol sprays and other solvents, Waste deposition in landfills, which generate methane.
Military uses, such as nuclear weapons, toxic gases, germ warfare and rocketry.
Natural sources
Dust from natural sources, usually large areas of land with little or no vegetation.
Methane, emitted by the digestion of food by animals, for example cattle.
Radon gas from radioactive decay within the Earth's crust.
Smoke and carbon monoxide from wildfires.
Volcanic activity, which produce sulfur, chlorine, and ash particulates.
Pollutants
A substance in the air that can be adverse to humans and the environment is known as an air pollutant. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made. Pollutants can be classified as primary or secondary. Usually, primary pollutants are directly produced from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone — one of the many secondary pollutants that make up photochemical smog. Some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include:
Sulfur oxides (SOx) - especially sulfur dioxide, a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
Nitrogen oxides (NOx) - especially nitrogen dioxide are expelled from high temperature combustion, and are also produced naturally during thunderstorms by electric discharge. Can be seen as the brown haze dome above or plume downwind of cities. Nitrogen dioxide is the chemical compound with the formula NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants.
Carbon monoxide (CO)- is a colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
Volatile organic compounds - VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is another dangerous compound which is often associated with industrial uses.
Particulates, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulates can be man made or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.
Persistent free radicals connected to airborne fine particles could cause cardiopulmonary disease.
Toxic metals, such as lead and mercury, especially their compounds.
Chlorofluorocarbons (CFCs) - harmful to the ozone layer emitted from products currently banned from use.
Ammonia (NH3) - emitted from agricultural processes. Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.
Odors — such as from garbage, sewage, and industrial processes
Radioactive pollutants - produced by nuclear explosions, nuclear events, war explosives, and natural processes such as the radioactive decay of radon.
Secondary pollutants include:
Particulates created from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
Ground level ozone (O3) formed from NOx and VOCs. Ozone (O3) is a key constituent of the troposphere. It is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant, and a constituent of smog.
Peroxyacetyl nitrate (PAN) - similarly formed from NOx and VOCs.
Minor air pollutants include:
A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive
A variety of persistent organic pollutants, which can attach to particulates
Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment.
Major air pollutants and their associated health hazards
Name of pollutant
|
Health impacts
|
RSPM
(Respirable
Particulate Matter)
|
Respiratory
illness, including chronic bronchitis and asthma; heart diseases.
|
SO2
|
Heart
diseases; respiratory problems including pulmonary emphysema, cancer, eye
burning, headache, etc.
|
NO2
|
Lung
irritation, viral infection, airway resistance, chest tightness, etc.
|
SPM
(Suspended
Particulate Matter)
|
Pneumoconiosis,
restrictive lung diseases, asthma, cancer, etc.
|
Benzene
|
It
causes immunotoxicity, carcinogenicity, asthma, anemia, unconsciousness etc.
|
Ozone
|
Impaired
lung function, chest pains, coughing, irritation of eyes, nose etc.
|
CO
|
CO
poisoning cause cherry lips, unconsciousness, death by asphyxiation etc.
|
Lead
|
It
causes decreased haemoglobin synthesis, anemia, damage the nervous and renal
(kidney) systems etc.
|
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