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Air Pollution

Life on Earth is supported by the atmosphere, as it provides the necessary gases for the process of photosynthesis and respiration. The ozone layer in the atmosphere protects life on Earth from the harmful ultraviolet radiations of the sun. Waste gases and particles are also dumped in the atmosphere which causes air pollution.
 
Pollutants can be natural occ
urring materials that are present in quantities larger than the normal. They can also be human-made materials. These pollutants make the atmospheric air impure and cause changes in the natural processes of the atmosphere and also harms living things. Greenhouse gases in excess raise global temperatures. Atmosphere is a dynamic fraction of the biosphere, it continuously absorbs a wide range of substances either solids, liquids or gases, may be from natural or man-made sources. 



Clean, dry air contains nitrogen 78.09% by volume and 20.94% oxygen. The remaining 0.97% is made of gaseous mixture of carbon dioxide, helium, krypton, argon, xenon and nitrous oxide and very small amounts of other organic and inorganic gases. Contaminants continuously enter the atmosphere through natural and man-made process on earth. These contaminants in the air causes toxicity, disease, aesthetic distress, physiological effects or environmental decay.  

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What is Air Pollution

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Air pollution is the contamination of the environment that modifies the natural characteristics of the atmosphere. These contaminants or pollutants can be any chemical, physical or biological agent. The introduction of these pollutants into the atmosphere cause discomfort, disease and even death to human beings; they also cause damage to other living organisms like food crops, damage to the natural environment. 

Air pollution can also be defined as "any atmospheric condition in which specific substances present in certain concentrations can cause undesirable effects on man and his environment.

Air pollution is the excessive concentration of foreign particles in the atmosphere which affects the well being of individuals or cause damage to property. 

Air Pollutants

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Pollutant is the substance in the air that can cause adverse effects on humans and the environment. Pollutants can be either solid particles, liquid droplets or gases. They may be from a natural source of man-made. 

The major pollutants are:
  • Sulphur dioxide: It is mainly produced by valcanoes and various industrial emissions. 
  • Nitrogen oxides - Oxides of nitrogen are emitted due to high temperature combustion, thunderstorms.
  • Carbon monoxide - It is emitted due to incomplete combustion of fuel. Emission from motor vehicles are the main source of carbon monoxide.
  • Volatile organic compounds - These are emitted from methane and other industrial uses.
  • Hydrocarbons
  • Inorganic particulate matter and aerosols
  • Organic particulate matter
  • Carbon dioxide
  • Hydrocarbons Polynuclear Aromatic Compounds and Polunuclear Aromatic Hydrocarbons
  • Chlorofluoro carbons
  • Peroxylacetyl Nitrate
  • Lead halides particulate matter
  • Asbestos Particles
  • Silicon dioxide
  • Pollen grains
  • Fungal spores, bacteria, virus, etc.

Causes of Air Pollution

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Air pollution is the change in the composition of air by the introduction of harmful substances like industrial and automobile emissions. 
Sources of air pollution are the various locations, activities or factors which are responsible for contributing pollutants into the atmosphere. The causes or the sources of air pollution can be of two major categories which are anthropogenic causes (man-made sources) and natural sources.

Anthropogenic Sources

  • Anthropogenic causes of air pollution are mostly related to burning of different kinds of fuels. 
  • Smoke stacks of power plants, factories and waste incinerators, furnaces and other types of fuel burning equipments. 
  • In developing countries burning of traditional biomass like wood, crop waste and dung are the major source of air pollution.
  • Motor vehicles, marine vessels, aircraft and sound effects are major mobile sources of air pollution.
  • Fumes from plant, hair spray, aerosol sprays, varnish and other solvents.
  • Deposition of waste in landfills generates methane. 
  • Military equipments like the nuclear weapons, toxic gases. germ warfare and rocketry also contribute to air pollution.
  • Chemicals used in household and farming cause pollution like crop dusting, fumigation of homes, domestic cleaning products and painting supplies. Also insect/pest killers, dust emitted from fertilizer introduce harmful chemicals into the air and cause pollution. 

Natural Sources

  • Dust from large areas of land with a few or no vegetation.
  • Emissions of methane gas due to digested food by animals, like cattle.
  • Gases like radon that is emitted from radioactive decay in the Earth's crust.
  • Carbon monoxide and smoke from wildfires.
  • Active volcanoes produce chlorine, sulfur and ash particulates. 

Indoor Air Quality

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Indoor Air Quality it the air quality inside and around building structures, it relates tot eh the health and comfort of the occupants of the building. The indoor air quality is affected by gases like carbon monoxide, radon, particulates, volatile organic compounds microbial contaminants. Common indoor air pollutants are second-hand smoke, radon, molds and other allergens, carbon monoxide, volatile organic compounds, and other bacteria, asbestos and carbon dioxide. 

Effects of Air Pollution

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Global Warming 
  • Due to the greenhouse effect every year the temperatures are rising. 
  • Pollution causes the levels of greenhouse gases to go up. This phenomenon is known as global warming. 
  • Global warming bring about climate changes,  climatic changes causes changes in the livelihood of plants and animals, disturbance in agriculture and food production, melting of snow caps and increase in sea levels. 
Photochemical Smog 
  • Pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight and form smog. 
  • Mixture of gases and photochemical reactions is called photochemical smog. 
Acid rain 
  • Sulphur dioxide and oxides of nitrogen react with water vapors of the atmosphere to produce sulphuric acid and nitric acid. 
  • This comes down along with rain water and is called as acid rain. Acid rains can cause respiratory and skin disorders, 
  • Damages leaves
  • Affects the soil pH and other conditions.
  • Causes harm to aquatic life entering into ground and river waters. 
  • Causes damage to monumental structures. 


Aerosols 
  • Aerosols affect the weather conditions by blocking solar radiations. 
  • Deposition of aerosols on leaves affects the process of photosynthesis
  • Also disperse metallic pollutants. 
Depletion of Ozone 
  • Molecules of hydrocarbons like the chloroflurocarbons deplete the ozone layer. 
  • Depletion of ozone layer lets in the harmful ultraviolet rays from the sun to the earth's surface. 
Harmful Effects of Air Pollution 
  • Air pollution causes breathing ailments like bronchitis, asthma, tuberculosis, pneumonia, lung cancer. 
  • It affects the central nervous system due to carbon monoxide poisoning. 
  • Fumes from pesticides, fungicides, insect repellents can be carcinogenic. 
  • Pollution due to heavy metals like lead cause anemia, convulsions, brain damage, problems in liver, kidney, circulatory  and nervous and death.
  • Fumes of pesticides like the DDT get biomagnified and cause disorder to kidney, brain and problems of circulatory system.  

Air Pollution Control

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Different methods can be used to control air pollution caused by pollutants of gaseous and particulate form. 

Techniques to control pollution caused by gases: Pollutants like sulphur dioxide, ammonina, hydrocarbons, carbon dioxide can be controlled by absorption, adsorption and combustion. 
  • Combustion - Organic pollutants can be controlled by subjecting them to flame combustion or catalytic combustion.
  • Absorption - Here, the polluted air contain gaseous pollutants is passed through a scrubber containing suitable liquid absorbent. 
  • Adsorption - in this technique, polluted air is passed through porous solid adsorbents an clean is passed out after process of adsorption. 

Methods to control particulate emissions: Pollution that is caused by particulate like ash, dust, soot, etc, can be controlled using wet scrubber, fabric filters, electrostatic precipitators and certain mechanical devices. 
  • Fabric Filters - The polluting particulate matter is passed through a porous medium made of woven or filled fabrics. This process of controlling fabric filters is called 'bag filtration'.
  • Wet Scrubbers - By passing fumes through water the wet scrubber trap SO2, NH3 and metal fumes.
  • Electrostatic Precipitators - Passage of polluted air through an electrostatic precipitator induces electric charge on the particles, these particles get precipitated on the electrodes.
  • Mechanical Devices - These devices work on the principles of gravity and sudden change in the direction of air flow. 
  • Gravity - Due to gravitational force the particulate matter settles down and gets removed.
  • Sudden change in the direction of air flow - Here the particles are separated due to greater momentum.  
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