Air Pollution

Prerequisites

Ecology and Environment, for ecosystems, food chains and the environmental laws in outline.
Chemistry in Everyday Life, for oxides, acids and combustion.

The Hook: Winter Haze over Korba

Connect

Drive into Korba on a December morning and the sun is a pale disc behind a grey haze. Coal-fired power stations, open fly-ash dykes, coal trucks on dusty roads and thousands of household chulhas all add to it, and cold, still winter air keeps the haze close to the ground. Yet Korba is also the Chhattisgarh city that has reported the largest fall in PM10 under the National Clean Air Programme.

So what exactly is in that haze, how is it measured, and which laws and programmes are meant to clean it?

Why it matters: Prelims asks about pollutants and their sources, AQI categories, smog types, acid rain and programmes such as NCAP. Mains P-IV (GS-II) asks for causes, health effects and remedies, and a Chhattisgarh example such as Korba or the sponge-iron belt makes an answer stand out.

Basic Terms

Air pollution (वायु प्रदूषण) is the presence in the atmosphere of substances in concentrations that harm human health, other living things or materials.

Term	Meaning	Example
Primary pollutant	Emitted directly from a source	SO₂, NO, CO, soot, fly ash
Secondary pollutant	Formed in the air by reactions between primary pollutants	Ground-level ozone, PAN (peroxyacetyl nitrate), sulphuric acid droplets, secondary particulate matter
Point source	A single identifiable outlet	A thermal power station chimney
Area / non-point source	Many small, scattered sources	Vehicles in a city, household chulhas, road dust

The Major Air Pollutants

Pollutant	Main sources	Key effects
PM10 (particles ≤ 10 µm)	Road and construction dust, mining, fly ash	Reach the nose, throat and upper airways; aggravate asthma
PM2.5 (fine particles ≤ 2.5 µm)	Combustion: vehicles, coal, biomass, crop-residue burning; secondary particles	Penetrate deep into the lungs and can enter the bloodstream; linked to heart and lung disease. The most harmful common pollutant
Sulphur dioxide (SO₂)	Burning coal and oil; metal smelting	Respiratory irritation; forms acid rain. Lichens are sensitive indicators of SO₂
Nitrogen oxides (NOₓ)	High-temperature combustion, especially vehicles and power plants	Respiratory irritation; acid rain; with hydrocarbons and sunlight forms photochemical smog and ozone
Carbon monoxide (CO)	Incomplete combustion: vehicle exhaust, chulhas, closed rooms with angithis	Binds haemoglobin about 200 times more strongly than oxygen, forming carboxyhaemoglobin; causes suffocation
Ground-level ozone (O₃)	Secondary: NOₓ + volatile organic compounds + sunlight	Chest pain, coughing; damages crops. Harmful near the ground
Lead (Pb)	Formerly leaded petrol; now batteries, smelting	Nervous-system damage, especially in children. India phased out leaded petrol by 2000
Ammonia (NH₃)	Fertilisers, livestock waste	Forms secondary particulate matter
Benzene, VOCs	Petrol vapour, solvents, paints	Benzene is carcinogenic (leukaemia)

Ozone: good up there, bad down here

Stratospheric ozone (the ozone layer, about 15–35 km up) shields life from ultraviolet radiation, and its depletion by CFCs is dealt with by the Montreal Protocol (see Environmental Conventions). Tropospheric (ground-level) ozone is a pollutant formed in smog. Same molecule, opposite roles.

Smog: two types

Feature	Classical (London / sulphurous) smog	Photochemical (Los Angeles) smog
Ingredients	Smoke + fog + SO₂	NOₓ + hydrocarbons + sunlight
Climate	Cool, humid	Warm, dry, sunny
Chemical nature	Reducing	Oxidising
Typical products	Sulphuric acid droplets, soot	Ozone, PAN, aldehydes
Famous episode	Great Smog of London, December 1952	Los Angeles, from the 1940s

Delhi’s winter smog combines both kinds: combustion particles from vehicles, industry and crop-residue burning, trapped by a temperature inversion (a warm air layer above cold surface air that stops pollutants from rising).

Acid rain (अम्लीय वर्षा)

Normal rain is slightly acidic (pH about 5.6) because dissolved CO₂ forms weak carbonic acid. Rain with pH below 5.6 is called acid rain.
Cause: SO₂ and NOₓ react with water vapour to form sulphuric acid and nitric acid.
Effects: acidified lakes and soils, leaching of nutrients, damage to forests, corrosion of buildings.
“Marble cancer”: acid deposition reacts with the calcium carbonate of marble. Concern over the Taj Mahal led the Supreme Court in M.C. Mehta v. Union of India (Taj Trapezium case, 1996) to order polluting industries in the Taj Trapezium Zone to shift to cleaner fuel or relocate.

Indoor air pollution

Cooking on biomass chulhas (wood, dung cakes, crop residue) in poorly ventilated kitchens exposes women and children to high levels of PM2.5 and CO. This is why clean cooking fuel is treated as a health measure: Pradhan Mantri Ujjwala Yojana (launched 1 May 2016 at Ballia, Uttar Pradesh) gives LPG connections to poor households. Other indoor pollutants include radon (a radioactive gas from soil and rocks), tobacco smoke and formaldehyde from furniture.

Measuring Air Quality

National Ambient Air Quality Standards (NAAQS), 2009

Notified by the CPCB in November 2009, the NAAQS cover 12 pollutants: PM10, PM2.5, SO₂, NO₂, CO, O₃, lead, ammonia, benzene, benzo(a)pyrene, arsenic and nickel.

Pollutant	Annual average	24-hour average	WHO Air Quality Guideline (2021)
PM2.5	40 µg/m³	60 µg/m³	5 µg/m³ annual; 15 µg/m³ 24-hour
PM10	60 µg/m³	100 µg/m³	15 µg/m³ annual; 45 µg/m³ 24-hour

India’s standards are much less strict than the WHO’s 2021 guidelines. WHO guidelines are advisory, not binding.

National Air Quality Index (AQI)

Launched in October 2014 under the Swachh Bharat Abhiyan, run by the CPCB.
Based on 8 pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃ and Pb. The overall AQI is the sub-index of the worst pollutant, not an average.
Six categories:

AQI	Category	Colour	Health impact (summary)
0–50	Good	Dark green	Minimal
51–100	Satisfactory	Light green	Minor breathing discomfort to sensitive people
101–200	Moderate	Yellow	Discomfort to people with lung or heart disease, children, older adults
201–300	Poor	Orange	Breathing discomfort to most people on prolonged exposure
301–400	Very Poor	Red	Respiratory illness on prolonged exposure
401–500	Severe	Maroon	Affects healthy people; serious impact on those with existing disease

Laws, Institutions and Programmes

Measure	Year	Key point
Air (Prevention and Control of Pollution) Act	1981	Gave the pollution control boards set up under the Water Act (1974) powers over air; states can declare air pollution control areas. Passed to implement the decisions of the Stockholm Conference (1972)
Environment (Protection) Act	1986	Umbrella law; emission standards for industries and vehicles are notified under it
CPCB (केंद्रीय प्रदूषण नियंत्रण बोर्ड)	1974	Statutory body under the Water Act; runs the National Air Quality Monitoring Programme and the AQI
Chhattisgarh Environment Conservation Board (CECB) (छत्तीसगढ़ पर्यावरण संरक्षण मंडल)	—	The state pollution control board, headquartered in Raipur. Grants consent to establish and operate industries
Bharat Stage VI	1 April 2020	Nationwide; India skipped BS-V and went straight from BS-IV. Sulphur in fuel cut to 10 ppm
National Clean Air Programme (NCAP)	Launched 10 January 2019	Time-bound national plan for 131 cities (non-attainment and million-plus cities). Original target: 20–30% cut in PM by 2024 (base 2017). Revised target: up to 40% reduction in PM10, or meeting NAAQS, by 2025-26 (base 2019-20). City action plans; performance-linked funds; PRANA portal for monitoring
Graded Response Action Plan (GRAP)	Notified 2017 for Delhi-NCR	Emergency measures that tighten in four stages as AQI worsens (Poor → Very Poor → Severe → Severe+). Now enforced by the Commission for Air Quality Management (CAQM) in NCR
Green crackers	From 2018-19	Developed by CSIR-NEERI (Nagpur); lower emissions than conventional firecrackers
Fly ash utilisation	Notifications from 1999 onwards	Thermal power plants must ensure use of fly ash in bricks, cement, roads and mine filling

Chhattisgarh angle

NCAP cities in Chhattisgarh (as of 2025): Raipur, Bhilai-Durg, Bilaspur and Korba. Reported 2024-25 data showed Korba with the steepest fall in PM10 (about 47% against its baseline), while Raipur, Bhilai-Durg and Bilaspur improved by smaller margins and missed the 40% mark. Quote these as “reported figures” and check the latest CPCB data.
Sources in the state: coal-based thermal power and fly-ash dykes in Korba (which has figured among the CPCB’s critically polluted industrial clusters); sponge iron (DRI) units and steel plants around Raipur (Siltara, Urla), Raigarh and Bhilai; coal and iron-ore mining dust; cement plants; open coal transport.
The CECB grants consents and monitors stacks. Mains answers can suggest continuous emission monitoring, covered coal transport, higher fly-ash use and stricter checks on DRI kilns.

Read more in Power Generation in Chhattisgarh.

Analysis for Mains

Why air pollution persists in India

Many diffuse sources: dust, vehicles, biomass burning and small industries are hard to regulate one by one.
Coal dependence in power and industry, especially in mineral states like Chhattisgarh.
Weak enforcement capacity of state pollution control boards (staff, monitoring stations).
Airsheds cross boundaries: smoke from one district or state settles in another, but plans are made city by city.
Meteorology: winter inversions and low wind speeds trap pollutants.

Way forward

Airshed-level planning across city and state boundaries.
Clean energy transition, electric public transport and stricter industrial emission norms with continuous monitoring.
Dust control (paved shoulders, covered trucks, water sprinkling) and better construction-site rules.
LPG and electric cooking to cut household smoke.
Public health communication: AQI alerts, masks and school schedules on bad-air days.

Memory Tricks

AQI's 8 pollutants: 'PM-PM, NOSe CO, Ozone Ammonia Lead'

PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, Pb. The NAAQS have 12: the same 8 plus Benzene, Benzo(a)pyrene, Arsenic and Nickel, “Big Bad Arsenic Nickel”.

AQI categories in order: 'Good Students Make Poor Very Poor Scores'

Good → Satisfactory → Moderate → Poor → Very Poor → Severe. Every band is 100 wide except the first two (50 each).

Smog types

London = Low sun, Lots of SO₂, reducing. LA = Lots of sunlight, NOₓ, oxidising (ozone, PAN).

Don’t Confuse

This	vs	That
PM10 — coarse, upper airways, dust	vs	PM2.5 — fine, deep in lungs and blood, combustion
AQI — 8 pollutants, 6 categories, a public communication index	vs	NAAQS 2009 — 12 pollutants, legal standards
Classical smog — SO₂, reducing	vs	Photochemical smog — NOₓ + sunlight, oxidising
Stratospheric ozone — protective	vs	Ground-level ozone — pollutant
NCAP — national, 131 cities, PM reduction targets	vs	GRAP — emergency stages for Delhi-NCR
Water Act 1974 — created CPCB and SPCBs	vs	Air Act 1981 — gave those boards air powers

Common Mistakes

MCQ traps

“The Air Act, 1981 created the Central Pollution Control Board.” False. The CPCB was set up under the Water Act, 1974. The Air Act extended its functions.
“AQI is the average of all pollutants.” False. It is the highest sub-index among the pollutants measured.
“Photochemical smog is reducing in nature.” False. It is oxidising; classical smog is reducing.
“India adopted BS-V before BS-VI.” False. India leapfrogged from BS-IV to BS-VI on 1 April 2020.
“Normal rain is neutral (pH 7).” False. Unpolluted rain is about pH 5.6; acid rain is below that.
“CO kills by blocking the airways.” False. It binds haemoglobin, reducing the blood’s oxygen-carrying capacity.

Practice

All questions below are original practice questions written in CGPSC style. They are not previous-year questions.

Level 1: Foundation

Rain is called acid rain when its pH falls below ______.
The National Air Quality Index uses ______ pollutants and ______ categories.
Which pollutant forms carboxyhaemoglobin in the blood?

Answers

5.6.
8 pollutants and 6 categories.
Carbon monoxide (CO).

Level 2: Prelims MCQs

Q1. Consider the following statements about the National Air Quality Index (AQI):

It is calculated as the average of the sub-indices of all pollutants measured.
Ammonia and lead are among the pollutants it covers.
An AQI value of 250 falls in the “Poor” category.

Which of the statements given above is/are correct?

(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer and explanation

(b) 2 and 3 only. The overall AQI equals the worst (highest) sub-index, not an average, so statement 1 is wrong. The eight AQI pollutants include NH₃ and Pb. The “Poor” band is 201–300, so 250 is Poor.

Q2. Match List I (Pollutant) with List II (Main concern):

List I	List II
A. Carbon monoxide	1. Acid rain; lichens are sensitive indicators
B. Sulphur dioxide	2. Nervous-system damage in children
C. Lead	3. Reduces the oxygen-carrying capacity of blood
D. Ground-level ozone	4. Secondary pollutant of photochemical smog

(a) A-3, B-1, C-4, D-2
(b) A-1, B-3, C-2, D-4
(c) A-3, B-1, C-2, D-4
(d) A-2, B-1, C-3, D-4

Answer and explanation

(c) A-3, B-1, C-2, D-4. CO forms carboxyhaemoglobin. SO₂ forms sulphuric acid in rain, and lichens die back where SO₂ is high. Lead is a neurotoxin. Ozone near the ground is formed from NOₓ and hydrocarbons in sunlight.

Q3. Photochemical smog differs from classical smog in that it:

(a) forms mainly in cold, humid weather
(b) is reducing in nature and rich in SO₂
(c) is oxidising in nature and contains ozone and PAN
(d) needs no sunlight to form

Answer and explanation

(c). Photochemical smog needs sunlight acting on NOₓ and hydrocarbons, and its products (ozone, PAN, aldehydes) are oxidising. Options (a) and (b) describe classical London-type smog.

Q4. Under the National Clean Air Programme (NCAP), which of the following cities of Chhattisgarh are covered (as of 2025)?

Raipur
Korba
Jagdalpur
Bilaspur

Select the correct answer:

(a) 1 and 2 only
(b) 1, 2 and 4 only
(c) 2, 3 and 4 only
(d) 1, 2, 3 and 4

Answer and explanation

(b) 1, 2 and 4 only. The NCAP list for Chhattisgarh comprises Raipur, Bhilai-Durg, Bilaspur and Korba. Jagdalpur is not on it. Of these, Korba reported the largest fall in PM10 by 2024-25.

Q5. The Central Pollution Control Board was originally constituted under:

(a) the Air (Prevention and Control of Pollution) Act, 1981
(b) the Environment (Protection) Act, 1986
(c) the Water (Prevention and Control of Pollution) Act, 1974
(d) the National Green Tribunal Act, 2010

Answer and explanation

(c). The CPCB and the state boards were created under the Water Act, 1974. The Air Act, 1981 entrusted the same boards with air pollution control. This is the most common trap in pollution-law questions.

Level 3: Mains Answer Writing

Q1. (60 words) Distinguish between classical smog and photochemical smog.

Model answer outline

Classical smog: smoke + fog + SO₂; cool humid weather; reducing; London 1952.
Photochemical smog: NOₓ + hydrocarbons + sunlight; warm dry weather; oxidising; products ozone and PAN; Los Angeles.
Conclusion: Indian cities such as Delhi show a mix of both in winter, worsened by temperature inversion.

Q2. (150–200 words) Discuss the major sources of air pollution in the industrial belts of Chhattisgarh and suggest measures to control it.

Model answer outline

Intro: Chhattisgarh’s mineral-based economy (coal, iron ore, steel, power, cement) brings high particulate pollution; four of its cities (Raipur, Bhilai-Durg, Bilaspur, Korba) are under NCAP.
Sources:
1. Coal-fired power plants and fly-ash dykes in Korba.
2. Sponge iron (DRI) and steel units around Raipur (Siltara, Urla), Raigarh and Bhilai.
3. Coal and iron-ore mining dust; open transport of coal on roads.
4. Cement plants, construction and road dust.
5. Household biomass burning in winter.
Measures: electrostatic precipitators and continuous emission monitoring; covered conveyors and rail sidings for coal; full fly-ash use in bricks and roads; green belts; LPG and clean cooking; strengthening the CECB’s monitoring network; NCAP city action plans with funds linked to results.
Chhattisgarh angle: Korba’s reported PM10 fall under NCAP shows targeted dust and stack control can work.
Conclusion: Balanced industrial growth needs an airshed approach that treats industry, transport and households together.

Quick Revision Table

Fact	Detail
PM2.5 vs PM10	≤ 2.5 µm (deep lungs, combustion) vs ≤ 10 µm (dust)
NAAQS	2009; 12 pollutants; PM2.5 40 annual / 60 daily µg/m³
WHO AQG 2021	PM2.5 annual 5 µg/m³
AQI	Oct 2014; 8 pollutants; 6 categories; worst sub-index
Acid rain	pH < 5.6; SO₂ and NOₓ
Classical smog	SO₂, reducing, London 1952
Photochemical smog	NOₓ + HC + sunlight; oxidising; O₃, PAN
CO	Carboxyhaemoglobin
Air Act	1981 (after Stockholm 1972)
CPCB	1974, under the Water Act
BS-VI	1 April 2020; BS-V skipped
NCAP	10 Jan 2019; 131 cities; up to 40% PM10 cut by 2025-26 (base 2019-20)
GRAP	Delhi-NCR; four stages; CAQM
CG NCAP cities	Raipur, Bhilai-Durg, Bilaspur, Korba
CECB	Chhattisgarh’s pollution control board, Raipur

Key Takeaways

PM2.5 is the most harmful common pollutant because it reaches deep into the lungs and blood.
Learn the AQI (8 pollutants, 6 bands) and the NAAQS (12 pollutants) separately.
Classical smog is reducing; photochemical smog is oxidising.
The CPCB came from the Water Act (1974); the Air Act (1981) widened its role.
In Chhattisgarh, coal power, sponge iron and mining drive air pollution; Raipur, Bhilai-Durg, Bilaspur and Korba are NCAP cities.

What’s Next

Water Pollution, the next topic in this chapter
Soil and Noise Pollution
Climate Change, where greenhouse gases and black carbon link to air quality
Energy Resources and Technology, for the clean-energy transition
Pollution and Waste — Quick Revision

Prerequisites

The Hook: Winter Haze over Korba

Basic Terms

The Major Air Pollutants

Smog: two types

Acid rain (अम्लीय वर्षा)

Indoor air pollution

Measuring Air Quality

National Ambient Air Quality Standards (NAAQS), 2009

National Air Quality Index (AQI)

Laws, Institutions and Programmes

Analysis for Mains

Memory Tricks

Don’t Confuse

Common Mistakes

Practice

Level 1: Foundation

Level 2: Prelims MCQs

Level 3: Mains Answer Writing

Quick Revision Table

Key Takeaways

What’s Next

Keep going in this chapter