The presence of materials in the air in such a concentration, which are harmful to man and the environment is called air pollution.
About 1×10^12 tons of emission enter air annually, of which 5×10^8 tons are emitted by man and the remaining by natural air pollution. Many pollutants do not rise above 600 meters of earth’s surface or they are diluted. So, air pollution affects locally than globally. All living organisms inhale a large quantity of air. An average human being breaths 22,000 times a day, inhaling 16kg of oxygen. About 98% of the total air pollution is accounted by the following pollutants globally. CO-52%, SO2-18%, Hydro carbons-12%, Particulars-10% and oxides of Nitrogen-6%. These pollutants are derived from natural sources and human activity. The surface of our planet consists of 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.03% CO2, water vapours and other gases. In addition, to these gases, particular matter such as pollen grains , dust algae, bacteria and spores of fungi causing different odours, vapours and fumes prevail in the air. Some of the substances are harmful to living organisms. The atmosphere is being continuously polluted with harmful materials by the activity of man.
TYPES OF AIR POLLUTION:
There are two basic types of pollutants in the air. They are known as primary pollutants and secondary pollutants.
Primary pollutants enter the air directly. Some are released by natural processes, like ash from volcanoes. Most are released by human activities.
Carbon oxides are released when fossil fuels burn.
Nitrogen oxides form when nitrogen and oxygen combine at high temperatures. This occurs in hot exhausts from vehicles, factories, and power plants.
Sulfur oxides are produced when sulfur and oxygen combine. This happens when coal that contains sulfur burns.
Toxic heavy metals include mercury and lead. Mercury comes from smokestacks. Both metals have industrial uses.
Volatile organic compounds (VOCs) are carbon compounds, such as methane. VOCs are released by many human activities. Raising livestock, for example, produces a lot of methane.
Particulates are solid particles. These particles may be ash, dust, or even animal wastes. Many are released when fossil fuels burn.
Secondary pollutants form from primary pollutants. Many occur as part of photochemical smog. This type of smog is seen as a brown haze in the air. Photochemical smog forms when certain pollutants have a chemical reaction in the presence of sunlight. Photochemical smog consists mainly of ozone (O3). Ozone near the ground is a pollutant (Figure below). This ozone is harmful to humans and other living things. However, ozone in the stratosphere protects Earth from the Sun’s harmful ultraviolet radiation.
SOURCES OF AIR POLLUTION:
“Most air pollution comes from energy use and production,” says John Walke, director of the Clean Air Project, part of the Climate and Clean Energy program at NRDC. “Burning fossil fuels releases gases and chemicals into the air.” And in an especially destructive feedback loop, air pollution not only contributes to climate change but is also exacerbated by it. “Air pollution in the form of carbon dioxide and methane raises the earth’s temperature,” Walke says. “Another type of air pollution, smog, is then worsened by that increased heat, forming when the weather is warmer and there’s more ultraviolet radiation.” Climate change also increases the production of allergenic air pollutants, including mold (thanks to damp conditions caused by extreme weather and increased flooding) and pollen (due to a longer pollen season).