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English · हिन्दी · తెలుగు · தமிழ் · മലയാളം · मराठी · ಕನ್ನಡ

Pollution: quick recap

Pollution · Quick recap · Fact-checked on · how we check

Written with AI from the sources listed at the bottom of this page, then fact-checked by a separate AI.

The whole chapter in one sitting: air pollutants, smog, acid rain and India's air standards and programmes; water quality, toxics, river cleaning, soil and noise; and the waste rules with extended producer responsibility.

Pollution is the addition of a substance or form of energy to air, water or soil in amounts that harm life or property. In air, primary pollutants such as sulphur dioxide and carbon monoxide leave their source already harmful, while secondary pollutants such as ground-level ozone form in the air itself. Fine particles (PM2.5) do the most damage to health. In winter, crop-residue smoke, calm air and temperature inversion trap pollution over the northern plains. Classical smog (London, 1952) is cold, coal-based and reducing; photochemical smog is sunny, traffic-based and oxidising. Acid rain, with a pH below 5.6, comes from sulphur dioxide and nitrogen oxides; in 1996 the Supreme Court protected the Taj Mahal through the Taj Trapezium Zone.

India measures air against the National Ambient Air Quality Standards of 2009, which cover 12 pollutants and set PM2.5 limits of 40 micrograms per cubic metre a year and 60 over 24 hours, far above the WHO guideline of 5 adopted in 2021. The National Air Quality Index (2014) uses eight pollutants and six categories, and the worst sub-index decides the reading. The National Clean Air Programme (2019) set reduction targets for cities that miss the standards. For Delhi and its region, the Graded Response Action Plan (2017) adds curbs stage by stage as the index worsens, and since 2021 the Commission for Air Quality Management runs it. Cleaner fuels did the rest: CNG for Delhi's buses (1998), the jump to Bharat Stage VI vehicles on 1 April 2020, ethanol blending and clean cooking gas.

Water quality is read through oxygen. Dissolved oxygen is what aquatic life breathes; biochemical oxygen demand is the oxygen microbes use to break down organic matter, so sewage pushes BOD up and DO down, and chemical oxygen demand is normally higher than BOD. In eutrophication, nitrogen and phosphorus feed algal blooms whose decay strips the water of oxygen. Toxic substances are a separate danger because they persist: mercury caused Minamata disease and cadmium itai-itai disease in Japan, natural arsenic poisons wells in the Ganga-Brahmaputra plains, excess fluoride causes fluorosis and nitrate causes blue baby syndrome. Persistent pesticides such as DDT accumulate in bodies and magnify up food chains. Remedies range from sewage treatment and river missions (Ganga Action Plan 1985, Namami Gange 2015) to clean-up by microbes and plants.

Noise is measured in decibels on a logarithmic scale, so every 10 dB rise means ten times the sound energy. The Noise Pollution (Regulation and Control) Rules, 2000, made under the Environment (Protection) Act, set day and night limits for industrial, commercial and residential areas and for the silence zone, the belt of 100 metres or more that surrounds a hospital, an educational institution or a court. Loudspeakers are barred at night, from 10 p.m. to 6 a.m., outside closed premises, and in 2005 the Supreme Court tied freedom from noise to Article 21. Thermal pollution lowers the oxygen in water, radioactive pollution damages cells and genes, light pollution misleads night-active animals, and oil spills smother the sea surface and seabirds.

Waste is handled by a family of rules made under the Environment (Protection) Act, most of them from 2016. The Solid Waste Management Rules make households segregate waste into wet, dry and domestic hazardous streams and make local bodies collect and process it, so that only inert residue reaches a sanitary landfill. For packaging, electronics and batteries the rules use extended producer responsibility: producers must collect or recycle what they sell and prove it with certificates. Plastic carry bags rose from 50 to 75 and then 120 microns, and identified single-use plastic items were banned from 1 July 2022. Bio-medical waste is sorted into yellow, red, white and blue containers; industrial hazardous waste is the factory occupier's duty; batteries, including electric-vehicle ones, have their own 2022 rules, and building debris is the builder's responsibility.

Pollution at a glance
PartCore ideasLaws, bodies and dates
1. AirPrimary and secondary pollutants, PM2.5, smog, acid rain, winter inversionNAAQS 2009; AQI 2014; NCAP 2019; GRAP 2017; CAQM 2021; BS-VI 2020; Taj Trapezium 1996
2. Water, soil, noiseDO, BOD, COD; eutrophication; heavy metals, arsenic, fluoride, nitrate; biomagnification; decibelsGanga Action Plan 1985; Namami Gange 2015; endosulfan ban 2011; Noise Rules 2000; Supreme Court 2005
3. WasteSegregation at source; processing before landfill; extended producer responsibilitySWM, Plastic, Bio-Medical, Hazardous and C&D Rules 2016; single-use plastic ban 2022; E-Waste and Battery Rules 2022

Exam traps

Recap

Practice questions

Q1. Photochemical smog differs from classical smog mainly because it:

  1. forms in cold, damp weather from coal smoke
  2. forms in sunny weather from nitrogen oxides and hydrocarbons and is oxidising
  3. contains mainly sulphuric acid droplets
  4. occurred first in London in 1952
Show answer

Answer: B. forms in sunny weather from nitrogen oxides and hydrocarbons and is oxidising

Photochemical smog needs sunlight acting on traffic gases and is oxidising. Cold damp weather with coal smoke, sulphuric acid droplets and the London episode of 1952 all describe classical smog, so options 1, 3 and 4 are wrong.

Q2. Consider the following statements about the National Air Quality Index:
1. It was launched in 2014.
2. The overall index is the average of the sub-indices of all pollutants measured.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: A. 1 only

Statement 1 is correct, so option 4 is wrong. Statement 2 is wrong because the worst sub-index, not the average, decides the overall index, so options 2 and 3 are wrong.

Q3. Which one of the following statements about water quality is correct?

  1. A higher BOD indicates cleaner water
  2. COD of a sample is normally higher than its BOD
  3. Warm water holds more dissolved oxygen than cold water
  4. Eutrophication increases dissolved oxygen in the long run
Show answer

Answer: B. COD of a sample is normally higher than its BOD

COD also counts matter microbes cannot digest, so it is normally above BOD. A higher BOD means more organic pollution; warm water holds less oxygen, which is why thermal pollution harms fish; and eutrophication lowers oxygen as dead algae decay, so options 1, 3 and 4 are wrong.

Q4. Consider the following pairs:
1. Minamata disease : Mercury
2. Fluorosis : Arsenic
3. Blue baby syndrome : Nitrate
Which of the pairs given above are correctly matched?

  1. 1 and 2 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: C. 1 and 3 only

Pairs 1 and 3 are correct. Pair 2 is wrong because fluorosis is caused by excess fluoride; arsenic causes skin lesions and cancers. So options 1, 2 and 4, which include pair 2, are wrong.

Q5. Consider the following statements:
1. Namami Gange was approved by the Union government in 2015.
2. The Ganga Action Plan was launched after Namami Gange, in 2018.
Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: A. 1 only

Statement 1 is correct, so option 4 is wrong. Statement 2 is wrong because the Ganga Action Plan came much earlier, in 1985, so options 2 and 3 are wrong.

Q6. Under the Noise Pollution (Regulation and Control) Rules, 2000, a silence zone is an area of at least 100 metres around:

  1. hospitals, educational institutions and courts
  2. airports and railway stations
  3. industrial estates
  4. national parks and sanctuaries
Show answer

Answer: A. hospitals, educational institutions and courts

The Rules define a silence zone around hospitals, educational institutions and courts. Airports, railway stations and industrial estates are noisy areas, not silence zones, and national parks are protected under wildlife law rather than declared silence zones by these Rules, so options 2, 3 and 4 are wrong.

Q7. Consider the following statements:
1. Under the Solid Waste Management Rules, 2016, households must segregate waste into three streams.
2. Extended producer responsibility applies to plastic packaging, e-waste and batteries.
3. The single-use plastic ban of 2022 prohibits all plastic packaging.
Which of the statements given above are correct?

  1. 1 and 2 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3
Show answer

Answer: A. 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is wrong: the ban covers a list of identified items, while packaging is managed through EPR, so options 2, 3 and 4, which include statement 3, are wrong.

Q8. Under the Bio-Medical Waste Management Rules, 2016, which colour of container is meant for glassware and metallic body implants?

  1. Yellow
  2. Red
  3. White (translucent)
  4. Blue
Show answer

Answer: D. Blue

Glassware and metallic implants go in blue. Yellow is for body parts, soiled dressings and discarded medicines; red for contaminated recyclable plastic items; white for sharps such as needles and blades.

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