Air Pollution and its Control

Pollution

Pollution is the undesirable change brought about by chemical, particulate matter, or biological materials to air, water, or soil.

Agents that bring about such an undesirable change are called as pollutants. In order to control environmental pollution, the Government of India has passed the Environment (Protection) Act, 1986 to protect and improve the quality of our environment (air, water and soil).

Air Pollution

Ø Air is a complex, dynamic natural entity, which is essential for supporting life on earth.

Ø Air pollutant is a substance that causes harm to the humans and other living organisms.

Ø Some of the common pollutants of air:

o Nitrogen dioxide

o Sulphur dioxide

o Carbon monoxide and carbon dioxide

o Volatile organic compounds

o Particulate matter

Control of Air Pollution

Air pollution causes severe respiratory disorders in humans and other animals and also affects plants. It can be controlled by the following ways:

Ø Fitting smokestacks and smelters, with filters to separate pollutants from the harmless gases.

Ø Particulate matter can be removed by using an electrostatic precipitator. It contains electrode wires maintained at several thousand volts, which produce electrons. These electrons cling on to dust particles and give them a net negative charge and are attracted by collecting plates, which are grounded. The velocity of air passing through the plates should be low enough to allow the dust to fall.

Ø A scrubber can be used to remove gases such as SO₂ wherein the exhaust passes through a spray of water or lime.

Ø Vehicular pollution can be reduced by using less polluting fuels such as CNG, which is more efficient and less costly as compared to petrol or diesel. In 2002, all the buses were switched to CNG in Delhi and this has indeed led to a fall in pollution levels in the city.

Ø Vehicles can be fitted with catalytic converters that have metals such as platinum, palladium, and rhodium as catalysts. These catalysts carry out the following conversions:

Unburnt hydrocarbons → CO₂ and H₂O

Carbon monoxide → Carbon dioxide

Nitric oxide → Nitrogen gas

Unleaded petrol must be used with catalytic converters as presence of lead in the petrol inactivates the catalyst.

Controlling Vehicular Air Pollution: A Case Study of Delhi

With its very large population of vehicular traffic, Delhi leads the country in its levels of air-pollution – it has more cars than the states of Gujarat and West Bengal put together. 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 very strongly by the Supreme Court, under its directives, 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.

CNG burns most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt. Moreover, CNG is cheaper than petrol or diesel, cannot be siphoned off by thieves and adulterated like petrol or diesel. The main problem with switching over to CNG is the difficulty of laying down pipelines to deliver CNG through distribution points/ pumps and ensuring uninterrupted supply. Simultaneously parallel steps taken in Delhi for reducing vehicular pollution include phasing out of old vehicles, 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.

The Government of India through a new auto fuel policy has laid out a roadmap to cut down vehicular pollution in Indian cities. More stringent norms for fuels means steadily reducing the sulphur and aromatic content in petrol and diesel fuels. Euro III norms, for example, stipulate 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 roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level to 35 per cent. Corresponding to the fuel, vehicle engines will also need to be upgraded.

Mass Emission Standards (Bharat Stage II which is equivalent to EuroII norms) are no more applicable in any of the cities of India.

Latest Mass Emission Standards in India

The air quality of Delhi has significantly improved. According to an estimate, a substantial fall in CO₂ and SO₂ level has been found in Delhi between 1997 and 2005.