Air Pollution



An air pollutant is known as a substance in the air that can cause harm to humans and the environment. 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 either primary or secondary. Usually, primary pollutants are substances directly emitted 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.


Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants in the atmosphere. These sources can be classified into two major categories which are:
Anthropogenic sources (human activity) mostly 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.
??? Marine vessels, such as container ships or cruise ships, and related port air pollution.
??? Burning wood, fireplaces, stoves, furnaces and incinerators .
??? Oil refining, and industrial activity in general.
??? Chemicals, dust and controlled burn practices in agriculture and forestry management, (see Dust Bowl).
??? Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.
??? Waste deposition in landfills, which generate methane.
??? Military, 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 Earths crust.
??? Smoke and carbon monoxide from wildfires.
??? Volcanic activity, which produce sulfur, chlorine, and ash particulates.
Major pollutants produced by human activity include:
??? Sulfur oxides (SOx) especially sulfur dioxide are emitted from burning of coal and oil.
??? Nitrogen oxides (NOx) especially nitrogen dioxide are emitted from high temperature combustion. Can be seen as the brown haze dome above or plume downwind of cities.
??? Carbon monoxide is 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.
??? Carbon dioxide (CO2), a greenhouse gas emitted from combustion.
??? Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.
??? Particulate matter (PM), measured as smoke and dust. PM10 is the fraction of suspended particles 10 micrometers in diameter and smaller that will enter the nasal cavity. PM2.5 has a maximum particle size of 2.5 ?ยตm and will enter the bronchies and lungs.
??? Chlorofluorocarbons (CFCs), harmful to the ozone layer emitted from products currently banned from use.
??? Ammonia (NH3) emitted from agricultural processes.
??? Odors, such as from garbage, sewage, and industrial processes
??? Radioactive pollutants produced by nuclear explosions, war explosives, and natural processes such as the radioactive decay of radon.
Health effects
The World Health Organization states that 2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution. Epidemiological studies suggest that more than 500,000 Americans die each year from cardiopulmonary disease linked to breathing fine particle air pollution. Worldwide more deaths per year are linked to air pollution than to automobile accidents. The health effects caused by air pollutants may range from subtle biochemical and physiological changes to difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions. The human health effects of poor air quality are far reaching, but principally affect the bodys respiratory system and the cardiovascular system.
Environmental impacts
The greenhouse effect is a phenomenon whereby greenhouse gases create a condition in the upper atmosphere causing a trapping of heat and leading to increased surface and lower tropospheric temperatures . A number of studies have also investigated the potential for long-term rising levels of atmospheric carbon dioxide to cause slight increases in the acidity of ocean waters and the possible effects of this on marine ecosystems.
Reduction efforts
There are various air pollution control technologies and urban planning strategies available to reduce air pollution.
Efforts to reduce pollution from mobile sources includes primary regulation. Many developing countries have permissive regulations, expanding regulation to new sources (such as cruise and transport ships, farm equipment, and small gas-powered equipment such as lawn trimmers, chainsaws, and snowmobiles), increased fuel efficiency (such as through the use of hybrid vehicles), conversion to cleaner fuels (such as bioethanol, biodiesel, or conversion to electric vehicles).
Control devices
The particulate controller, scrubber, Nox Controller and Acid Gas/So2 Controller are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.
Air pollution is usually concentrated in densely populated metropolitan areas, especially in developing countries where environmental regulations are generally relatively lax or nonexistent. Hence enforcing strict laws and abiding the same by the citizens can only control and reduce air pollution to a great extent.