Air Pollution

Air pollution is defined as the imbalance in the quality of air due to some natural processes or human activities so as to cause adverse effect on living organisms existing on earth. The polluted air is undesirable for breathing, for the condition of building and monuments exposed to it or for animal and plant life.

Air pollutants are the fatcors which cause air pollution. There are four notorious air pollutants:-

1. Oxides of sulphur (SO_x); emitted by power station and industries
2. Oxides of nitrigen (NO_x); emitted by power station, industries and vechicles
3. Oxides of carbon (CO_x) ; emitted by vechicles and dust
4. Suspended particularmatter (SPM) ; from combustion of dust

Air pollutants are categorized into two groups ;-

1. Primary air pollutants :

   They are the harmful substances which directly enter into the air due to natural events or man made activites. For exmaple:- burning of fossil fuels produces CO and CO₂.

   2C + O₂→ 2CO

   C + O₂ → 2CO₂

2. Secondary air pollutants:
   

   They are also the harmful substances which are produced into the air due to chemical reaction in between two or more componets. For example :- primary pollutants SO₂ comcines with aerial oxygen to give SO₃as the secondray pollutant.

   2SO₂+ O₂ → 2SO₃

   SO₃ + H₂O → H₂SO₄

   2CO + O_{2 →} 2CO₂

   CO₂ + H₂O → H₂SO₄

Sources of air pollution

Natural sources

1. Volcanic eruption
   It releases hot lava and huge and dense cloud of dust in the atmosphere.Chemical fumes released are rich in sulphur. Methane and other gases are also emitted.
   
   
2. Forest fires
   Fires in the forest may arise by lighting and friction between dried vegetation. These fires normally spread to large areas and throw out large quantities of semi burnt ash, unburnt hydrocarbon, carbon monoxide, nitrogen oxides etc.
   
   
3. Vegetation
   Plants produce pollen grains which float in the air and cause allergy in many persons. Trees give out volatile organics which react with atmosphere gases to produce the blue haze over the forests.
   
   
4. Dust stroms
   The Strong wind carries dust particles from one place to another. Dust is deposited on vegetation and household things. Pollen and other microbial life from distant region reaches to new places and may cause allergy and health problems. Fungal spores, bacteria and virus reach to long distance by wind and spread viral fevers and several other diseases some of which became epidemic.
   
   
5. Release of organic substances
   Organic substances like methane, ethane, ethene etc are released into the air by the biological decomposition of organic matter, seepage from natural gas and oil fields and volatile emission from plants.
   
   
6. Other natural sources
   Oceans are the most common sources of emission of fine particles of common salt into the atmosphere. Constant exposure to salt badly affects people, buildings and household wares. Soil erosion also pollutes air by spreading dust particles in the atmosphere.

Artificial sources

1. Automobile exhausts
   Automobile exhausts are the major sources of air pollution in urban areas, especially in big cities. Carbon monoxides, oxides of nitrogen, benzopyrene, ethene etc. are produced due to incomplete combustion of gasoline (petrol, diesel etc). Lead is also emitted when leaded gasoline is used.
   
   
2. Industrial exhaust
   Industries like paper and pulp factories, sugar factories, petroleum refineries, steel plants, bricks factories,food and beverage factories etc. are the major air polluting agents. They release harmful gases like CO, CO₂, SO₂, NO₂, NO, Cl₂ , F₂, NH₃, naphths vapour etc. and particulate matter into the atmosphere.
   
   
3. Pesticides
   pesticides like insecticides, herbicides, fungicides, rodenticides, etc. which are used in agricultural fields are also released to air as pollutants.
   
   
4. Photochemical smog
   When different gases likeSO₂, NO₂, NO, N₂O, unburnt hydrocarbons etc. are released into the atmosphere, they form photochemical smog (smoke + fog ) which becomes the harmful pollutant.
   
   
5. Particulate matter
   Small, solid particles and liquid droplets are collectively termed particulates. They are produced by man-made activities like fly ash from power plants, melters and mining operations and smoke from incomplete combustion processes.
   
   
6. Release of CFCs and ammonia
   CFC and ammonia are released into the atmosphere from air-conditioners, refrigerators, precooler system of cold storage and during the manufacture of nitric acid. Ammonia is also released from ammonium fertilizer plants.
   
   
7. War explosives
   During the explosion of sophisticated explosives in warfare, a number of poisonous gases are evolved which cause air pollution.
   
   
8. Tobacco smoke
   Millions of people of the world smoke cigarettes, bodies, hukkas etc releasing harmful compounds into the atmospheric air.
   
   
9. Release of radio isotopes
   Radio isotopes are releasedinto the atmosphere due to explosions of nuclear weapons, emissions from nuclear reactors in power generation, research and medicine. The gaseous radio isotopes are Ar-41, Xe-133, I-133, Kr-85, H-3, C-14, I-131etc

Effects of air pollution

Effets of air polution are various. Some common and major effects are given below:

1. Air pollution affects human health, animals, and plants causing global effects.
   
   
2. Lung cancer is a disease caused by polluted air which leads to death. It is mostly associated with respiratory diseases ranging from common cold to lung cancer.
   
   
3. Gaseous and particulate pollutants cause emphysema, bronchitis and asthma. Polluted air irritates the eyes and pollutants like lead accumulate in the body.
   
   
4. The prominent gaseous pollutants are carbon monoxide, sulphur dioxide, oxides of nitrogen, hydrogen sulphide, certain acid, aldehydes and hydrocarbons.
   
   
5. The particulate pollutants include dust, silicious matter and asbestos. Carbon monoxide reacts with the haemoglobin reducing the oxygen-carrying capacity of blood. Persons suffering from anaemia are more prone to get affected as carbon monoxide leads serious injuries.
   
   
6. Sulphur dioxide is the most serious and widespread air pollutant as lower levels of sulphur dioxide cause temporary spasm of the smooth muscles of the bronchia.
   
   
7. Higher concentration of sulphur dioxide induces increased mucus production. The cilia protecting respiratory system is affected by it causing cough, shortness of breath, spasm of the larynx, acute irritation of the eye membranes resulting in tears and redness.
   
   
8. Oxides of nitrogen are pulmonary irritants and excess concentration lead to pulmonary haemorrhage.
   
   
9. Hydrogen sulphide is well known for its characteristic rotten-egg odour. Hydrocarbons emitted from automobile exhaust cause lung cancer.
   
   
10. Other serious dust diseases include block lung disease from inhaling coal dust, berylliosis from beryllium dust, byssinosis that is cotton dust.
    
    

Control of air pollution

Air pollution creates the adverse effects on mankind, other animals, plants and vegetation, buildings and other constructions. Therefore it must be controlled without any delay. Following are the some of the control measures:

1. There should be massive afforestation programme in the industrial areas and big cities because plants absorb CO₂ in photosynthesis process and release oxygen.
   
   
2. Air pollution causing materials should be reduced, recycled and reused. It is the principle of green chemistry.
   
   
3. Dependence on fossil fuel should be reduced and alternative source of energy like sun, wind , water etc much be increased.
   
   
4. Use of unleaded petrol should be made compulsory.
   
   
5. Use of low sulphur fuel should be encouraged.
   
   
6. Nuclear reactor should be perfectly maintained and nuclear tests should be banned.
   
   

References :

Adhikari, N.R. Plus two practical chemistry. Nepal: Ed-mark Academic Enterprises Pvt. Ltd, 2004.

Jain, S.K. Conceptual Chemistry, Vol. I and II. S. Chand & Company Ltd., n.d.

Khatri, S.S. Elementary Principles of General Chemistry. TU Kathmandu: Curriculum Development Centre , 1997.

Wagley, Dr. P. Compressive Chemistry. Nepal: WorldWide Publication Pvt. Ltd, 2014.