Pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere.
Indoor air pollution and urban air quality are listed as two of the world's worst pollution problems in the 2008 Blacksmith Institute World's WorstPolluted Places report.
Pollutants
A substance in the air that can cause harm 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.
Classification
Primary pollutants are directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas froma 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.
Major primary pollutants produced by human activity include:
* sulfur dioxide, a chemical compound produced by volcanoes and in variousindustrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
* nitrogen dioxide are emitted from high temperature combustion, and are also produced naturally during thunderstorms by electrical discharge. Can be seen as thebrown haze dome above or plume downwind of cities.
* Carbon monoxide is a colourless, odorless, 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 a colourless, odorless, non-toxic greenhouse gas also associated with ocean acidification, emittedfrom sources such as combustion, cement production, and respiration
* Toxic metals, such as lead, cadmium and copper.
* Chlorofluorocarbons harmful to the ozone layer emitted from products currently banned from use.
* Odors — such as from garbage, sewage, and industrial processes
* Radioactive pollutants - produced by nuclear explosions, nuclear events, war explosives, and naturalprocesses such as the radioactive decay of radon.

Secondary pollutants include:
* 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 theatmosphere by ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
* Ground level ozone 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 chemicalprocesses 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.
Sources
Anthropogenic sources (human activity) mostly related to burning different kinds of fuel
* smoke stacks of power plants, manufacturing facilities and waste incinerators,as well as furnaces and other types of fuel-burning heating devices. motor vehicles, marine vessels, aircraft and the effect of sound etc.
* Chemicals, dust and controlled burn practices in agriculture and forestry management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. Fire is a natural part...