Environmental Chemistry: Air Pollution, Particulate Pollutants and Hydrocarbons (For CBSE, ICSE, IAS, NET, NRA 2022)

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Air Pollution

Undesirable changes have occurred in the physical and chemical constituents of air due to human activities. Undesirable change in the atmosphere is air pollution.

Types of Air Pollution

Particulate Pollutants

  • Particulate pollutants released by various industries as by-products of industrial processes. They are blown away by wind when they come out of the chimneys and other outlets of industries and mix with air. Suspended particulate matter is also emitted by exhaust of polluting diesel vehicles and ill managed coal fired power plants.
  • Examples of particulate pollutants are soot, flash from thermal power plants, cement dust, Petro coke from petroleum refineries.

Some of the particulate pollutants are discussed in detail below:

  • Dust: Particulate matter less than 10 microns in size is dust. It reaches lungs, deposits along the respiratory tract and causes asthma or even lung cancer. Dust from stone crushers is another example of particular pollutant.
  • Sodium chloride: Sodium chloride is used to remove snow in winter and remains in the environment. Some sodium chloride is also added to the environment when waves of the sea spray it. Excess sodium chloride has been found to cause defoliation (leaf falling) , suppression of flowering and breaking of terminal shoots of apple.
  • Agricultural chemicals: Chemical insecticides, herbicides and other pesticides are known to have damaging effects on plants. They are toxic to animals and humans also. Residues of pesticides get suspended as particulate matter in air.
  • Lead: Lead particles come into air from automobile exhausts. Lead is used as an antiknock agent in automobile gasoline which contains tetraethyl lead. Paint, ceramic and pesticide industries also add lead particles to the atmosphere.

Hydrocarbons

  • Hydrocarbons which may be in the form of liquid droplets or gas pollute air. As liquid droplets they spill or are added through seepage of oil fields and natural gas leakage. Methane is emitted in the swamps and paddy fields by methanogenic bacteria. Methane is also generated in stomachs of ruminant animals.
  • Incomplete combustion of fuels release 3,4 benzopyrene which causes lung cancer.
  • Pesticides, paints and solvents also release hydrocarbons.

Gaseous Pollutants

, , nitrogen oxides are commonly added to the air by human activities. Excess of these have very serious damaging effects on the physical environment as well as on humans.

  • Nitrogen Oxides: Anaerobic breakdown of nitrogenous compounds by bacteria is the natural source of nitrogen oxides. Burning fossil fuel also releases them. Power generators, automobile exhausts, explosives and nitrogenous fertilizer industries and the other anthropogenic sources produce nitrogen oxides.
  • : causes early dropping off of leaves and fruits in plants. Nitrogen oxides are one source of photochemical smog, acid deposition and greenhouse effect.
  • Tobacco smoke: Smoke from burning cigarettes or bidis contains nicotine, aromatic hydrocarbons and tar. These cause problems of blood pressure and heart, windpipe and lungs in the smoker as well as those around the smoker. Cigarette smoke is also carcinogenic.
  • Photochemical oxidants: Primary pollutants such as nitrogen oxides and hydrocarbons mix in the atmosphere and form secondary pollutants like peroxyacetyl nitrate (PAN) and ozone, under the influence of UV radiation from the sun.

Control of Air Pollution

  • Limiting pollutants into air by using Sulphur free oil and coal, using catalytic convertors in automobiles and avoiding burning of waste material.
  • Taking stringent measures against release of emissions from industries.
  • The other approach is to use sources of energy other than fossil fuels such as wind, water, solar power, etc. Use bicycles and battery powered cars rather than vehicles with internal combustion engines. Service vehicles should use lead free petrol.

Photo- Chemical Smog

  • Smog is a combination of fog, smoke and fumes released by mills and factories, homes and automobiles.
  • Pollutants like Sulphur dioxide which is released while burning Sulphur containing fuels (fossil fuels) and particulate matter like soot present in stagnant air masses, get modified in sunlight and form a sheet called photochemical smog.

Temperature Inversion

Temperature inversion causes smog to settle and remain near the ground till wind sweeps it away. Normally, warm air rises up into atmosphere. When a layer of cool air at the ground level is held there by an overlying layer of warm stagnant air. It is called temperature or thermal inversion.

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