Kinds of Pollution

(a) On the basis of origin : It is of two types

(i) Natural Pollution : Pollution caused by natural phenomena like emission of large quantity of toxic gases and particulate matter by volcanoes, landslides, forest fires, marsh gas, U.V. rays etc.

(ii) Anthropogenic Pollution : It is man made pollution caused by human activities like noise, automobiles, pesticides, industries etc. Its magnitude is quite less as compared to Natural Pollution. Anthropogenic pollution can be personal (smoking), community level (thermal power plant) or occupational (flour mill dust). For example; 0.05% of atmospheric pollution is man made while 99.95% is natural pollution.

(b) On the basis of physical nature: It may be gaseous, dust, thermal, noise or radioactive pollution depending on physical nature of pollutants.

(c) On the basis of part of environment: Pollution may be broadly classified as air, water and soil pollution.

(d) On the basis of emission: Pollution is classified as :

(i) Point source: Pollution is being emitted from a single point or definite source. e.g. municipal sewer passing into water body.

(ii) Non point source: Pollution is being emitted from a large area. e.g., agricultural run off

(iii) Area source: Whole area like mining area is producing pollution. e.g., mining area, industrial complex.

Classification of Pollutants

1. Based upon their natural disposal, pollutants are of two types:

(i) Biodegradable pollutants: These are easily decomposable wastes by natural processes and also by some artificial methods which include microbial action and radiations. Domestic sewage is the main pollutant of this category.

(ii) Non-degradable pollutants: These are generally not degraded or degraded at a very slow pace by the natural biological processes. e.g., aluminium cans, mercurial salts, long chain phenolic chemicals, DDT, arsenic salts of heavy metals, glass, tin containers, radioactive materials and plastics. These not only accumulate but often get biologically magnified.

2. According to their existence in nature, the pollutants may be quantitative or qualitative.

(i) Qualitative pollutants: They are pollutants which do not normally occur in the environment but are passed into it through human activity e.g., DDT and other pesticides, fungicides, herbicides, etc.

(ii) Quantitative pollutants: They become pollutants only when their concentration reaches beyond a critical value in the environment e.g., CO, CO2, nitrogen oxides.

3. On the basis of form of pollutants in which these persist after their release into the environment, these are again of two types:

(i) Primary pollutants: These are emitted directly in the environment from some definite sources such as particles of metals, carbon, DDT, tar, resin, pollen, fungi, bacteria, silicates, plastics, sulphur compounds in the form of SO2, SO3, H2S; carbon compounds in the form of CO, CO2; nitrogen compounds (NOx).

(ii) Secondary pollutants: These are formed by the reactions of primary pollutants in the environment e.g., a photochemical reaction occurs in the presence of bright sunlight between nitrogen oxide and waste hydrocarbons to form peroxyacetyl nitrate (PAN), Ozone (O3) etc.

AIR OR ATMOSPHERIC POLLUTION

It is defined as occurrence or presence of any material or gas in the air in such a concentration which is harmful to man, vegetation, animals and their environment.

With the gradual increase in the number of industries and automobiles, air pollution has now reached menacing proportions in big cities and industrial centres.

I. Causes / sources of air pollution

Various sources of atmospheric pollution are as follows :

1. Fossil fuels and fibres: Incomplete and complete combustion of the carbon contents of fossil fuel wood and charcoal produce carbon monoxide and carbon dioxide alongwith sulphur dioxide.

2. Emission from vehicles : Emission from automobiles, locomotives, aircrafts and exhausts in cities constitutes the major part of the total air pollution.

3. Industries: Industries add various harmful gases like CO, CO2, SO2, H2S, NO, hydrocarbons and small particles of dust, carbon, metals, radioactive materials etc. to the atmosphere.

4. Natural sources: Volcanic eruptions, forest fires, natural organic and inorganic decays, marsh gases, pollen grains of flowers, fungal spores, etc.

5. Metallurgical processing

II. Common air pollutants and their effects

These are basically of two types i.e. gaseous materials, particulate matter.

1. Gaseous Materials :

(a) Carbon monooxide : It is a product of incomplete combustion of fossil fuels (charcoal, coal mines). 50% emissions are contributed from automobiles. It produces COHb (carboxyhemoglobin) and reduces O2 carrying capacity of blood, resulting in giddiness, decreased vision, headache, cardiovascular malfunction and asphyxia.

(b) Hydrocarbons (HCs) or Volatile organic carbons (VOCs) : They are produced naturally (e.g., CH4) or due to incomplete combustion as unburnt discharges. These may lead to produce secondary pollutants, when combines with NOx Benzene and HCHO are carcinogenic and causes irritation of eyes and mucous membrane and causes bronchial constriction. HCHO released from newly formed carpets lead to indoor pollution.

(c) SO2: It is produced during combustion of sulphur containing fossil fuels, smelting of ore and from oil refineries. It causes eye irritation, severe respiratory problems, inhibits ET8 in plants. Also responsible for classical smog (London smog or sulphurous smog) acid rains and stone cancer. SO2 causes phaeophytization in lichens. So their absence is indicator of SO2 pollution. This may cause discolouration and deterioration of buildings, sculptures (yellowning of Taj Mahal is reported to be caused by SO2 pollution released by Mathura oil refinery).

(d) Nitrogen oxides (NOx) : Mainly produced during combustion of fossil fuels at high temperature in automobile engines (mainly NO and NO2). Nitrogen oxides cause the brown air that leads to heart and lung problems.

Secondary Air Pollutants:

Formed through a reaction between primary pollutants and often are more toxic.

Oxides of nitrogen reacts with hydrocarbons in presence of sunlight to produce PAN and O3.

In trophosphere the O3 is a chemical weed and can cause eye irritations and sometimes prove fatal, while PAN can have damaging effect on eyes and may induce respiratory distress. It can inhibit ETS in chloroplast and may results in silvering or glazing of leaves.

Smog : Opaque or dark fog having smoke, dust, water vapours and gases.

Acid Rain

The term was given by Robert Augus.

It is rainfall with a pH of less than 5.65. It is due to oxides of sulphur and nitrogen.

There are two types of acid deposition -wet and dry deposition.

About half of the acidity in the atmosphere is transferred to earth through dry deposition.

65% acid rain is due to SO2 emission, 30% due to nitrogen oxides and 5% due to release of hydrogen chloride from chemical industries.

Acid rain damages foliage and growing points of plants and causes leaching of essential minerals of soil.

It corrodes metals, marble, painted surface, slate, stone etc.

This phenomenon is called stone leprosy.

2. Particulate Matter:

These are added into the air by industries automobiles and by many operations like blasting, drilling, crushing, grinding, mixing etc.

These pollutants may be either solid or liquid particles. It is differentiated into Settleable ( 10 µm, settles out in less than one day) and Suspended ( 10 µm) remaining in air for weeks.

Some particulate matters are given below:

(a) Aerosols. These are the vapour chemicals in the form of fluorocarbons, chlorofluorocarbons, oxides of sulphur and nitrogen released into the air with force by the emission of jet and supersonic aeroplane emissions. Fog is an aerosol of water droplets in air. Aerosols are also used as disinfectants, in refrigeration and in the formation of certain solid plastic foams.

(b) Smoke. Similar to dust but consists of visible suspension of carbon and other particles given off by burning and smouldering organic matter. Smog is a combination of smoke, chemical fumes and fog. It remains suspended for many days and envelops the entire industrial area like a thick blanket due to stagnant air. It produces respiratory problems in humans such as asthma and bronchitis. Smoke does not allow a clear view of nature's beauty. The power stations throw out large amount of fly ashes (fine particulate matter passed out alongwith gases during burning of coal).

(c) Dust and mist. Dust (more than 1µm), Mist (more than 1 µm but liquid). These releases from industries and may cause a variety of diseases like, cotton dust produces lung fibrosis called byssinosis. Lung fibrosis produced in other industries includes asbestosis (in asbestos industry), silicosis (stone grinders), siderosis (iron mill), coal miners pneumoconiosis, flour mill pneumoconiosis etc. Manganese poisoning has been reported in welders.

(d) Pollen, spores, cysts and bacteria. Air borne organic constituent like pollens, spores, cysts, fungi, bacteria, fur, etc. may cause allergic reactions, bronchial asthma, emphysema, T.B. and lung cancer. The number increases in certain seasons. Skin allergy and asthma like diseases are very common from Parthenium plant in India. The hay fever from pollen allergy is very common.

III. Control of air pollution

1. Separation of pollutants from harmless gases

(i) Control equipments in industries such as gravity settling tanks, cyclone collectors, remove and precipitate large and small pollutant particles and thus, minimise the air pollution. Electrostatic precipitators are used in thermal power plants. These can remove over 99% particulate matter present in the exhaust from a thermal power plant.

Fig. : (A) Scrubber; (B) Electrostatic preCipitator

It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.

These electrons attach to dust particles giving them a net negative charge.

The collecting plates are grounded and attract the charged dust particles.

The velocity of air between the plates must be low enough to allow the dust to fall.

A scrubber can remove gases like sulphur dioxide.

In a scrubber, the exhaust is passed through a spray of water or lime.

Recently we have realised the dangers of particulate matter that are very very small and are not removed by these precipitators.

According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter are responsible for causing the greatest harm to human health.

These fine particulates can be inhaled deep into the lungs and can cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature deaths.

Catalytic converter have expensive metals, namely platinum, palladium, rhodium and can convert NOx to nitrogen and CO to CO2.

(ii) Controlling Vehicular Air Pollution -A Case Study of Delhi :

(a) Delhi leads the country in its levels of air-pollution -it has more cars than the states of Gujarat and West Bengal put together. In the 1990s, Delhi ranked fourth among the 41 most polluted cities of the world. Air pollution problems in Delhi became so serious that a public interest litigation (PIL) was filed in the Supreme Court of India. After being censured, the government was asked to take, within a specified time period, appropriate measures, including switching over the entire fleet of public transport, i.e., buses, from diesel to compressed natural gas (CNG). All the buses of Delhi were converted to run on CNG by the end of 2002.

Advantages of CNG

1. CNG burns most efficiently.

2. CNG is cheaper than petrol or diesel.

3. Cannot be siphoned off by thieves and adulterated like petrol or diesel.

4. The main problem that government has faced is the difficulty of laying down pipelines to deliver CNG through distribution points/pumps and ensuring uninterrupted supply.

Use of unleaded petrol, use of low-sulphur petrol and diesel, use of catalytic converters in vehicles, application of stringent pollution-level norms for vehicles, etc. are other steps taken to reduce pollution in Delhi.

(b) Stringent norms for fuels were given in new auto fuel policy for steadily reducing the sulphur and aromatic contents in petrol and diesel fuels. Euro-II norms, for example, stipulates that sulphur be controlled at 350 parts-per-million (ppm) in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42 per cent of the concerned fuel. The goal, according to the road map prepared by Indian Government, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level to 35 per cent. Vehicle engines will also need to be upgraded.

(c) The Bharat Stage II (equivalent to Euro-II norms), which is currently in place in Delhi, Mumbai, Kolkata, Chennai, Bangalore, Hyderabad, Ahmedabad, Pune, Surat, Kanpur and Agra, will be applicable to all automobiles throughout the country from April 1, 2005. All automobiles and fuelpetrol and diesel -were to have met the Euro-III emission specifications in these 11 cities from April 1, 2005 and have to meet the Euro-IV norms by April 1, 2010. The rest of the country will have Euro-III emission norm compliant automobiles and fuels by 2010.

(d) A substantial fall in CO2 and S02 level has been found in Delhi between 1997 and 2005.

(iii) Height of chimneys in industries should be increased to the highest possible level to reduce smoke pollution at ground level.

(iv) Trees purify the air by consuming CO2 and releasing oxygen. Trees should be grown in all available places. Certain plants like Phaseolus vulgaris, Coleus blumei, Daucus carota and Ficus variegata fix carbon monoxide of the air. Similarly Vilis, Pinus, Juniperus, Pyrus, and Robinia pseudoacacia etc. are capable of metabolising oxides of nitrogen and other gaseous pollutants. These plants certainly help in reducing air pollution to a great extent.

2. Avoidance of Air Pollutants

(a) Industries should be set up at a far off distance from residential areas.

(b) Air pollution boards should enforce emission standards, frame rules and regulation for the control of air pollution.

(c) Firewood, coal and oil should be completely replaced by nuclear power, solar power, tidal power, wind power, natural gas or electricity which do not emit oxides of carbon, sulphur or nitrogen in the air.

(d) Automobile use should be minimised which emits high amount of air pollutants.

(e) Human population growth should be checked which is the major cause of air pollution.