Table of Contents
- Air Pollution: Air Pollutants, Classification of Air Pollutants (Previous Post)
- Effects of Air Pollution: Acid Rain and Ocean Acidification (Previous Post)
- Controlling Air Pollution: Bharat Stage VI, National Air Quality Index (This Post)
- Air pollution may be defined as the presence of any solid, liquid or gaseous substance including noise and radioactive radiation in the atmosphere in such concentration that may be directly and/or indirectly injurious to humans or other living organisms, property or interferes with the normal environmental processes.
- An ever-increasing use of fossil fuels in power plants, industries, transportation, mining, construction of buildings, stone quarries had led to air pollution.
- Fossil fuels contain small amounts of nitrogen and sulphur.
- Burning of fossil fuels like coal (thermal power plants) and petroleum release different oxides of nitrogen and sulphur into the atmosphere.
- These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain.
- Acid rain corrodes the marble monuments like Taj Mahal. This phenomenon is called as Marble cancer.
- Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and as pressurising agents in aerosol sprays. CFCs damage the ozone layer of the atmosphere.
- The combustion of fossil fuels also increases the number of suspended particles in the air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.
- Presence of high levels of all these pollutants causes visibility to be lowered, especially in cold weather when water also condenses out of the air. This is known as smog and is a visible indication of air pollution.
Smog is already explained in detail in Geography > Climatology > Forms of Condensation > Smog
Ozone Depletion is already explained in detail in Geography > Climatology > Polar Vortex > Ozone Depletion
- Paints, carpets, furniture, etc. in rooms may give out volatile organic compounds (VOCs).
- Use of disinfectants, fumigants, etc. may release hazardous gases.
- In hospitals, pathogens present in waste remain in the air in the form of spores.
- In congested areas, slums and rural areas burning of firewood and biomass results in lot of smoke.
- Children and ladies exposed to smoke may suffer from acute respiratory problems.
- Use of wood and dung cakes should be replaced by cleaner fuels such as biogas, LPG or electricity. The use of solar cookers must be encouraged.
- Those species of trees such as baval (Acacia nilotica) which are least smoky should be used.
- Charcoal is a comparatively cleaner fuel.
- Indoor pollution due to the decay of exposed kitchen waste can be reduced by covering the waste properly.
- Segregation of waste, pre-treatment at the source, sterilisation of rooms will help.
- Industrial pollution can be greatly reduced by:
- use of cleaner fuels such as liquefied natural gas (LNG) in power plants, fertiliser plants etc. which is cheaper in addition to being environmentally friendly.
- employing environment-friendly industrial processes so that emission of pollutants and hazardous waste is minimized.
- installing devices which reduce the release of pollutants.
- Devices like filters, electrostatic precipitators, inertial collectors, scrubbers, gravel bed filters or dry scrubbers are described below:
- Filters remove particulate matter from the gas stream.
- Baghouse filtration system is the most common one and is made of cotton or synthetic fibres (for low temperatures) or glass cloth fabrics (for higher temperature up to 2900 C).
- Electrostatic precipitation can remove over 99 per cent particulate matter present in the exhaust.
- The emanating dust is charged with ions, and the ionised particulate matter is collected on an oppositely charged surface.
- An electrostatic precipitator 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 (relatively positive charge) and attract the charged dust particles.
- The velocity of air between the plates must be low enough to allow the dust to fall.
- The particles are removed from the collection surface by occasional shaking or by rapping the surface.
- ESPs are used in boilers, furnaces, and many other units of thermal power plants, cement factories, steel plants, etc.
- It works on the principle that inertia of SPM (suspended particulate matter) in gas is higher than its solvent and as inertia is a function of the mass of the particulate matter, this device collects heavier particles more efficiently (centrifugation is the technique).
- ‘Cyclone’ is a common inertial collector used in gas cleaning plants.
- Scrubbers are wet collectors. They remove aerosols from a stream of gas either by collecting wet particles on a surface followed by their removal or else the particles are wetted by a scrubbing liquid.
- The particles get trapped as they travel from supporting gaseous medium across the interface to the liquid scrubbing medium. (this is just like mucus in trachea trapping dust)
- A scrubber can remove gases like sulphur dioxide.
- Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing the emission of poisonous gases.
- As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
- Motor vehicles equipped with catalytic converter should use unleaded petrol because the lead in the petrol inactivates the catalyst.
Apart from the use of the above mentioned devices, other control measures are:
- increasing the height of chimneys.
- closing industries which pollute the environment.
- shifting of polluting industries away from cities and heavily populated areas.
- development and maintenance of a green belt of adequate width.
- The emission standards for automobiles have been set which if followed will reduce the pollution.
- Standards have been set for the durability of catalytic converters which reduce vehicular emission.
- In cities like Delhi, vehicles need to obtain Pollution Under Control (PUC) certificate at regular intervals.
- This ensures that levels of pollutants emitted from vehicles are not beyond the prescribed legal limits.
- The price of diesel is much lower than petrol which promotes the use of diesel. To reduce the emission of sulphur dioxide, sulphur content in diesel has been reduced to 0.05%.
- Earlier lead in the form of tetraethyl lead was added in the petrol to raise octane level for the smooth running of engines. Addition of lead in petrol has been banned to prevent the emission of lead particles.
- Usage of alternative fuels like CNG in public transport vehicles is made mandatory in cities like Delhi. 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 aromatics content in petrol and diesel fuels.
- The goal, according to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level of aromatic hydrocarbons to 35 per cent.
BS VI from 2020
- From April 2017, BS IV norms are applicable nationwide.
- October 2018: Supreme Court ordered a ban on the sale of Bharat Stage IV vehicles from April 1, 2020.
- The central government had announced the April 1, 2020 deadline for adopting Bharat Stage VI emission norms by manufactures.
Bharat Stage (BS) norms
- The BS norms are instituted by the government to regulate the emission of air pollutants from motor vehicles.
- The norms were introduced in 2000.
- The norms limit the release of air pollutants such as nitrogen oxides, carbon monoxide, hydrocarbons, particulate matter (PM) and sulphur oxides from vehicles using internal combustion engines.
- The norms are meant to be adopted by using appropriate fuel and technology.
- As the stage goes up, the control of emissions become stricter.
- BS IV and BS VI norms are based on similar norms in Europe called Euro 4 and Euro 6.
- As decided initially, BS V would have been rolled out by 2021 and BS VI in 2024, but leapfrog to BS VI norms by 2020 (skipping BS V) had to be done because of the carbon footprint obligations.
India’s UNFCCC commitments (Intended Nationally Determined Contributions)
- Improve the emissions intensity of its GDP by 33 to 35 per cent by 2030 below 2005 levels.
- Increase the share of non-fossil fuels-based electricity to 40 per cent by 2030.
- Enhance forest cover which will absorb 2.5 to 3 billion tonnes of carbon dioxide by 2030.
Differences between BS IV and BS VI
- The extent of sulphur is the major difference between Bharat Stage IV and Bharat Stage VI norms.
- BS-IV fuels contain 50 parts per million (ppm) sulphur; the BS-VI grade fuel only has 10 ppm sulphur.
- BS VI can bring
- PM in diesel cars down by 80 per cent.
- nitrogen oxides from diesel cars by 70 per cent and in petrol cars by 25 per cent.
- BS VI also makes onboard diagnostics (OBD) mandatory for all vehicles.
- OBD device informs the vehicle owner or the repair technician how efficient the systems in the vehicle are.
- RDE (Real Driving Emission) will be introduced for the first time that will measure the emission in real-world conditions and not just under test conditions.
- Bharat Stage VI norms will also change the way particulate matter is measured. It will now be measured by number standard instead of mass standard.
- Compliance requires a higher investment in technology to make new vehicles.
- Upgrading vehicles in stock is an additional burden for the manufacturers.
- BS Vl-compliant vehicles will be expensive.
- BS Vl-compliant fuel too will be more expensive.
- Central Pollution Control Board (CPCB) has been executing a nationwide programme of ambient air quality monitoring known as National Air Quality Monitoring Programme (NAMP).
The National Air Quality Monitoring Programme (NAMP) is undertaken
- to determine the status and trends of ambient air quality;
- to ascertain the compliance of NAAQS;
- to identify non-attainment cities;
- to understand the natural process of cleaning in the atmosphere; and
- to undertake preventive and corrective measures.
The NAAQS have been revisited and revised in November 2009 for 12 pollutants, which include
- sulphur dioxide (SO2),
- nitrogen dioxide (NO2),
- particulate matter having micron (PM10),
- particulate matter having a size less than 2.5 microns (PM2.5),
- carbon monoxide (CO),
- ammonia, and
- Launched by the Environment Ministry in April 2015.
- Initiative under ‘Swachh Bharat’.
- It helps the common man to judge the air quality within his vicinity.
- Index constituted as a part of the Government’s mission to improve the culture of cleanliness.
Old vs new
- While the earlier measuring index was limited to three indicators, the current measurement index had been made quite comprehensive by the addition of more parameters.
Previously who measured Air pollution
- Central Pollution Control Board along with State Pollution Control Boards have been operating the National Air Monitoring Program (NAMP).
Why is AQI necessary?
- Quality of data from some cities remains weak, and the standards set for pollutants fall short of World Health Organization recommendations.
- The pollution related analysis using a vast number of complex parameters was complicated for the common man to understand.
Categories of air pollution under AQI
- There are six AQI categories, namely Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe.
Q. In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of Air Quality Index? (2016)
- Carbon dioxide
- Carbon monoxide
- Nitrogen dioxide
- Sulphur dioxide
Select the correct answer using the code given below.
- 1, 2 and 3 only
- 2, 3 and 4 only
- 1, 4 and 5 only
- 1, 2, 3, 4 and 5
Answer: b) 2, 3 and 4 only
- Government is disincentivising use of private vehicles through congestion charging.
- The National Green Tribunal has ordered that diesel vehicles over 10 years old not ply on Delhi roads.