What is Air Pollution ?
Air is an important natural resource providing the basis of life on earth. Entire biosphere depends on air. Air in the atmosphere provides oxygen to plants and animals, by virtue of which they are able to live. The composition of air (78% N, 21% O, and 0.03% CO2) is necessary to be maintained for the continuance of life on earth. Impairment of composition of air directly affects the living of plants and animals - as the life process would be curtailed in case of reduction in oxygen content in air.
Polluting such a natural resource by various human activities will substantially change the composition of air. This may lead to many short term and long term implications on the life of plants and animals. Besides the change in composition, the pollution may directly add some poisonous and harmful gases - which may cause series of health complications.
Types of Air Pollution
Based on the possible reasons, air pollution could be classified into
- Accidental air pollution
- Industrial air pollution
- Transport related air pollution
- Dwelling related air pollution
1. Accidental air pollution is further classified into:
- Air pollution by forest fires
- Air pollution by accidents to petroleum mass transport vehicles
- Air pollution by leakage, blasts in industries
2. Industrial air pollution can be
- Pollution from thermal power plants
- Pollution due to chemical fertilizers, food, pesticide and pharmaceutical industries
- Pollution due to cement, steel, paper, sugar industries
- Pollution due to textile and textile related industries
- Pollution due to petroleum and other industries
- Pollution due to atomic units
3. Transport related air pollution can be
- Pollution due to all types of terrestrial transport system
- Pollution due to urban transport system
- Pollution due to other modes of transport
4. Dwelling related air pollution can be
- Pollution due to use of aerosols
- Pollution due to high density of population
- Pollution due to waste disposal system
Out of them, major contribution of air pollutants is from industrial pollution and transport related pollution - because industrial activity and transport are continuously operative. Industrial growth and growth in transport sector are regarded as important components of growth of national economy itself. Hence, these two continuously operating and growing sectors, contribute pollutants at a growing rate. Air pollution due to accidents is occasional. But they may be dangerous to emit large quantity of pollutant at a time. Dwelling related pollution is more correlated to wide spread use of advanced technologies like computers, refrigerators, air conditioners etc., as well as miss-handling or no-handling of waste disposal systems in urban agglomeration. A significant contribution is also made by natural respiration of thickly populated urban population.
Formation of photochemical smog
When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight, smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it is called the photochemical smog. The word 'smog' is derived from the two words - smoke and fog.
It forms a yellowish brown haze especially during winter and hampers visibility. It also is a cause of many respiratory disorders and allergies as it contains polluting gases.
Photochemical smog is mainly composed of ozone (O3), peroxyacetyl nitrate (PAN) and NOx. It is also known as brown air where solar radiation is intense. In seasons of lesser solar radiation or areas, smog formation is incomplete and the air is referred to as grey air.
A simplified set of photochemical reactions involved in smog formation is as follows:
Reactions occurring inside engine:
Reactions occurring in atmosphere:
Smog ozone may damage plant as well as animal life. Several species of plants are very susceptible to PAN in smog. PAN damages choloroplasts, which results in reduction of photosynthetic effeciency and growth of plants.
Effects of Air Pollution
Air pollution can cause number of health hazards to human beings, animals, birds, in addition to causing number of deleterious effects on earth's atmosphere as well as vegetation and even on some buildings. It is a global malady causing innumerable irreversible changes to our planet. The effects of air pollution have no limitations or country boundaries. They can extend to any adjoining country or even far off country from the country of origin.
Pollution, in general, is not caused by anybody deliberately. Air pollution is the result of many activities - which are as normal as human diet in life. But, effects of such pollution are far reaching and irreversible. The dangerous effects of some important air pollutants on human health are discussed here.
Carbon monoxide (CO)
It has strong affinity to combine/bind with haemoglobin in blood to form carboxyhaemoglobin, which reduces oxygen carrying capacity of blood to cause headache,nausea ,asphyxiation and fainting (low supply of O2 to body though one may inhale normally). Against normal level of 0.5% CO in blood, severe pollution may lead to 8 to 9% CO.
Carbon dioxide (CO2)
It is estimated that in the last 100 years 360 billion tons of CO2 is added to atmosphere. CO2 has risen by 7% in the last 30 years. As CO2 in atmosphere has capacity to trap infrared rays in the band with 2.1 to 15mm, higher CO2 in atmosphere has caused global warming (rise in temperature). This is also known as “green house effect”. Global warming has number of effects like rise in sea water level and increase in incidence of some diseases. Increased CO2 level in air has also caused imbalance in atmosphere and reduced supply of O2.
Carbon disulphide (CS2)
It is highly dangerous gas causing mental illness like depression, anorexia, insomnia, loss of memory. It can also cause other effects like loss of sensation, muscular weakness, loss of vision, dizziness, and symptoms of Parkinson's disease.
Also called as freons, they belong to a group called chlorofluorocarbons (CFC). They are used as propellant in aerosols or as refrigerants in domestic refrigerators, deep freezers, air conditioners. CFM are not disintegrated in air, but rise to troposphere. There they are dissociated due to ultra violet rays to release free chlorine. This nascent chlorine causes ozone depletion, as ozone gas has strong affinity to react with free chlorine gas. Thinning of ozone shield will allow UV-radiations in earths atmosphere and cause extensive damage to planets and animals.
Methane has capacity to mix with blood haemoglobin to form methamoglobin - which has no capacity to carry O2 like normal haemoglobin. This reduces oxygen supply to body causing asphyxia.
Methyl Iodide (CH3I)
It can cause cancerous tumours in respiratory tracts.
Sulphur dioxide (SO2)
Excess SO2 levels in air can lead to some consequences like:
Lead to acid rain - which is the result of
- That is SO2 is converted into sulphite in presence of atmospheric oxygen. SO3 (sulphite) can mix with rain water to bring mild sulphuric acid to earth's surface during its movement.
- Inhalation of sulphur dioxide damages the respiratory tract very badly causing inflammation, irritation, ulcers as well as disruption of alveoli activity.
- SO2 + atmospheric humidity (H2O) can result into fine particles of sulphites and H2SO4. They are often attached to dust or fine carbon particles released out of vehicular pollution. When inhaled they have capacity to damage delicate tissue linings to eyes, nose, respiratory tract, inhibit cilial action in nose.
- Cyanide gases (Hydrogen cyanide - HCN, Methyl isocyanide CH3CN)
Highly dangerous gases are often released out of leakages in chemical industries. They are also released in metal finishing processes like electroplating, case hardening activities. They are fatal in their action causing instant deaths if exposed to such gas for 3 - 5 minutes continuously. In milder form, it can cause damage cells of bronchi, alveoli, nasal tract. It can also lead to many heart problems and vision problems.
Chlorine Gas (Cl)
Chlorine is a highly irritant gas with possible damages like skin irritation, eye irritations, and throat irritation leading to inflammation and disfunction on long exposure to chlorine gas.
Hydrogen Chloride (HCl)
HCl gas is also an irritant gas that causes damages to skin, eyes, throat, and nasal tract. It is also corrosive, damaging the cells.
Gaseous ammonia is a pungent, irritant gas often causing effects like skin irritation, eye irritation and irritation to throat. It can cause number of allergies.
Control of Air Pollution
Checking the air pollution by strict imposition of laws on factories.
- Reducing vehicular traffic and encouraging public transport vehicles than individual vehicles.
- Use of unleaded petrol.
- Regular check of exhaust gases from vehicles to declare their status in respect of pollution.
- Ban and imposition of fines on polluting vehicles.
- Strict control measures to take care of accidental pollution by industries.
- Safe burial of atomic wastes.
- Raising the height of chimneys of factories so that pollutant gas released from chimneys will reach upper strata of atmosphere.
- Ban on illegal burning of hazardous materials and illegal handling of radioactive materials.