Air Pollution Types Sources Control | Environment Notes for UPSC IAS 2025

Air Pollution: Types, Sources, and Control Measures (UPSC Prelims + Mains)

Air pollution means harmful substances are present in the air in a quantity that can damage human health, plants, animals, materials, or the climate. In India, it is a major public health and governance issue because it affects crores of people daily—especially in cities, industrial clusters, and the Indo-Gangetic Plain during winter.

The Polluter Pays Principle: The legal doctrine mandates that the costs of environmental remediation be borne by the party responsible for the pollution.

For UPSC, air pollution connects directly with: Environment, Health, Governance, Economy, Agriculture, Urban planning, Disaster-like episodes (smog), and India's global commitments on climate and sustainable development.

1) What is Air Pollution?

📘 Air Pollution

The presence of solid particles, liquid droplets, or gases in the air at levels that are harmful to living beings, ecosystems, and property.

📘 Pollutant

Any substance (gas/particle) that reduces air quality and can cause harm, such as PM2.5, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, etc.

📘 Emission vs Concentration

Emission is what comes out from a source (vehicle/industry). Concentration is what we measure in the air around us (ambient air quality). Weather can increase or reduce concentration even if emissions remain same.

📘 Ambient Air

Outdoor air in our surroundings (streets, parks, markets, villages, cities). Pollution here is called ambient air pollution.

📘 Indoor Air Pollution

Pollution inside homes/buildings due to cooking fuels, ventilation issues, smoke, chemicals, and burning activities (incense, mosquito coils, etc.).

2) Major Air Pollutants You Must Know (UPSC Prelims)

In India, commonly monitored "criteria pollutants" include particulate matter and key gases. These are important for both MCQs and Mains answers.

Pollutant	What it is	Common sources in India	Why it matters
PM10	Particles ≤ 10 microns	Road dust, construction dust, mining, industry	Breathing issues, cough, eye irritation
PM2.5	Fine particles ≤ 2.5 microns	Vehicle exhaust, coal burning, biomass burning, secondary formation	Enters deep into lungs; higher risk for heart and lung diseases
NOx (NO, NO2)	Nitrogen oxides	Vehicles, thermal power plants, industries	Forms ozone and secondary particles; irritates lungs
SO2	Sulfur dioxide	Coal power plants, refineries, some industries	Acid rain; respiratory irritation; forms sulfate particles
O3 (Ground-level ozone)	Secondary pollutant formed in sunlight	Formed from NOx + VOCs (vehicles, solvents, industries)	Breathing difficulty; damages crops like wheat and rice
CO	Carbon monoxide	Incomplete burning (vehicles, biomass, generators)	Reduces oxygen delivery in body; dangerous in indoor settings
NH3	Ammonia	Agriculture (fertilisers), animal waste	Forms secondary particles (ammonium salts)
Pb	Lead (heavy metal)	Some industrial processes, battery recycling	Neurotoxin; harms children's brain development

📘 VOCs

Volatile Organic Compounds are carbon-based gases from fuels, solvents, paints, and industries. VOCs react with NOx in sunlight to form ground-level ozone and photochemical smog.

3) Types of Air Pollution

3.1 Primary vs Secondary Air Pollutants

📘 Primary Pollutants

Pollutants emitted directly from a source. Example: CO from vehicle exhaust, SO2 from coal burning, soot/black carbon from diesel engines.

📘 Secondary Pollutants

Pollutants formed in the atmosphere due to chemical reactions. Example: ground-level ozone (O3), secondary sulfates and nitrates that add to PM2.5.

UPSC angle: Many high PM2.5 episodes are not only direct smoke/dust. A large part can be "secondary" particles formed from NOx, SO2, NH3, and VOCs under suitable weather conditions.

3.2 Particulate vs Gaseous Pollution

Particulate pollution: PM10, PM2.5, soot, dust, smoke, ash, pollen.
Gaseous pollution: NO2, SO2, CO, O3, NH3, VOCs.

3.3 Indoor vs Outdoor (Ambient) Air Pollution

Indoor: Solid fuel cooking, poor ventilation, tobacco smoke, mosquito coils, cleaning chemicals, dampness and mould.
Outdoor: Traffic emissions, construction dust, industrial stacks, open burning, crop residue burning, power plants.

3.4 Smog Types (Very Important for Prelims + Mains)

📘 Smog

A mixture of smoke + fog-like conditions where pollutants and moisture reduce visibility and harm breathing.

Photochemical smog: Common in sunny conditions; formed by NOx + VOCs → ozone and other irritants. Often seen in large cities with heavy traffic.
Sulfurous smog: Linked with SO2 and particulate emissions from coal burning in cool, humid conditions.

3.5 Particle Size Classification (PM Focus)

Category	Size	Where it comes from	Health risk
Coarse particles	PM10 (2.5–10 microns)	Dust, construction, road re-suspension	Upper respiratory irritation
Fine particles	PM2.5 (≤ 2.5 microns)	Combustion, secondary formation	Deep lung penetration; higher disease risk
Ultrafine particles	< 0.1 micron	High-temperature combustion (vehicles)	Can enter bloodstream; serious risk

4) Sources of Air Pollution

4.1 Natural Sources

Dust storms (especially in summer in north-west India and adjoining regions).
Forest fires (seasonal fires add smoke and PM).
Sea salt aerosols in coastal areas.
Pollen and biological particles.

Natural sources matter, but in most Indian cities, the major controllable part is from human activities.

4.2 Anthropogenic (Human-made) Sources

Air pollution is usually a "multi-source" problem. That is why single-step solutions rarely work.

A) Transport (Urban + Highway)

Tailpipe emissions: PM2.5, NOx, CO, VOCs.
Non-exhaust emissions: tyre wear, brake wear, road dust re-suspension.
Congestion increases emissions because engines idle longer.

📘 Non-Exhaust Emissions

Pollution not coming from the engine exhaust, such as brake dust, tyre wear particles, and dust re-suspended by moving vehicles.

B) Industry and Thermal Power Plants

Coal-based power: SO2, NOx, PM, mercury traces, fly ash.
Industries (steel, cement, refineries, chemicals): dust, SO2, NOx, VOCs.
Small industries in clusters may lack strong pollution control systems.

C) Construction and Road Dust

Building construction, demolition, uncovered material transport.
Unpaved shoulders and poor road maintenance increase dust.
Common in fast-growing cities like Delhi-NCR, Bengaluru, Hyderabad, and many tier-2 cities.

D) Residential (Household) Sources

Solid fuels (firewood, dung cakes, crop waste) create heavy PM2.5 inside homes.
Poor ventilation increases exposure, especially for women, children, and elderly.

UPSC governance link: Clean cooking connects environment with health, gender, and welfare policy (example: LPG connections under schemes launched in 2016).

E) Agriculture and Biomass Burning

Crop residue burning (notably in parts of Punjab, Haryana, and western UP) adds PM, CO, NOx, and VOCs.
Fertiliser use releases NH3 which helps form secondary PM2.5.

F) Waste Burning and Landfills

Open burning of municipal waste releases toxic fumes (including dioxins/furans in some cases).
Landfills release gases; fires in landfills can create severe smoke episodes.

G) Brick Kilns, Diesel Generator Sets, Mining

Traditional brick kilns can be highly polluting (PM, SO2) if technology and fuels are poor.
Diesel generators used during power cuts emit PM and NOx.
Mining and stone crushing generate heavy dust.

H) Firecrackers (Short-term Peaks)

Cause sharp spikes in PM and some metals.
Impact becomes worse if weather is calm and cold (low mixing height).

5) Why Air Pollution Becomes Severe in North India During Winter (Concept + Geography)

📘 Temperature Inversion

Normally, air near ground is warmer and rises, helping pollutants disperse. In winter nights, the ground cools fast and cold air stays near the surface, trapping pollutants below a warm layer above.

📘 Mixing Height

The vertical height up to which air mixes well. Low mixing height in winter means pollutants stay concentrated near the ground.

Cold and calm conditions: Low wind speed reduces dispersion.
Temperature inversion: Traps pollutants near the surface.
High emissions season: Biomass burning, higher heating needs, festivals, traffic.
Geography of Indo-Gangetic Plain: Large basin-like region can trap pollution under stable atmosphere.

Prelims tip: Pollution is not only about "how much we emit". It is also about meteorology (wind, inversion, humidity, rain) and topography.

6) Impacts of Air Pollution

6.1 Human Health Impacts

Short-term: Eye irritation, cough, asthma attacks, breathlessness, headaches.
Long-term: Higher risk of chronic respiratory disease, heart disease, stroke, lung cancer.
Children: Reduced lung growth, more infections.
Pregnancy: Higher risk of low birth weight and complications.

📘 Why PM2.5 is More Dangerous

PM2.5 particles are tiny, reach deep into lungs, and some can enter bloodstream. That is why PM2.5 is often linked with high long-term health burden.

6.2 Environmental Impacts

Reduced visibility: Smog reduces road safety and affects tourism.
Acid rain: SO2 and NOx can form acids in rain, damaging soils, buildings, and water bodies.
Crop loss: Ground-level ozone damages leaves and reduces yield (important for wheat, rice, and pulses).
Ecosystem stress: Airborne nitrogen deposition can disturb natural nutrient balance.

📘 Acid Rain

Rainwater that becomes more acidic due to gases like SO2 and NOx converting into sulfuric and nitric acids in the atmosphere.

6.3 Climate Link (Environment + GS3 Integration)

Black carbon (soot): Warms the atmosphere and can darken हिमालय glaciers when deposited, speeding melting.
Some aerosols: Can reflect sunlight and cause cooling, but they harm health.
Ozone: Also acts as a greenhouse gas near the ground.

6.4 Economic and Social Impacts

Higher healthcare spending and productivity loss.
School closures and restricted outdoor activities during severe smog.
Damage to buildings and monuments due to corrosion and soot deposition.

7) Measurement and Monitoring: AQI and Standards

📘 AQI (Air Quality Index)

A single number used to communicate how polluted the air is on a given day. Higher AQI means worse air quality and higher health risk.

India uses monitoring stations (manual and continuous) to track pollutants. The goal is to use data for early warning, policy action, and accountability.

7.1 Common Monitoring Tools

CAAQMS: Continuous Ambient Air Quality Monitoring Stations (real-time).
Emission monitoring: Stack monitoring in industries, and in many cases continuous monitoring systems.
Source apportionment studies: Identify sector-wise contribution (traffic, dust, industry, biomass, etc.).

7.2 Why Data Alone is Not Enough

Monitoring tells "what is in air", but solutions need "who is emitting what" (emission inventory).
Enforcement capacity and coordination across departments are key.

8) Control Measures: The Complete UPSC Framework

Control measures should follow a simple logic: Prevent emissions → Reduce at source → Capture/treat → Manage exposure. The best approach is airshed-based (regional), not only city-based.

📘 Airshed Approach

Managing air pollution by considering the full region where air moves (districts/states), because pollution does not follow city or state boundaries.

8.1 Legal and Institutional Measures (India)

Air (Prevention and Control of Pollution) Act, 1981: Main law to prevent and control air pollution.
Environment (Protection) Act, 1986: Umbrella law enabling standards and rules.
NAAQS (2009): National Ambient Air Quality Standards define acceptable limits.
NCAP (2019): National Clean Air Programme for city action plans and monitoring improvement.
GRAP (2017): Graded Response Action Plan for emergency measures in Delhi-NCR.
CAQM (2021): Commission for Air Quality Management for NCR and adjoining areas.
Bharat Stage (BS) norms: BS-VI implemented from 2020 for cleaner vehicle standards.

Mains note: Mentioning the year makes your answer sharper and more credible.

8.2 Sector-wise Control Measures (Most Scoring Part in Mains)

Sector	Main pollutants	High-impact control measures
Transport	PM2.5, NOx, CO, VOCs	BS-VI compliance, strong PUC + inspection, public transport and metro, EV buses, better traffic flow, parking management, non-motorised transport
Power plants	SO2, NOx, PM	FGD for SO2 control, low-NOx burners, high-efficiency ESP/bag filters, cleaner coal handling, continuous monitoring
Industries	PM, SO2, NOx, VOCs	Scrubbers, bag filters, cleaner fuels (PNG), leak detection for VOCs, stricter compliance and audits, relocation/zoning where needed
Construction & Dust	PM10, PM2.5	Covering materials, dust screens, sprinkling, mechanised sweeping, paving shoulders, strict demolition norms
Households	PM2.5, CO	Clean cooking fuels (LPG/PNG/electric), improved stoves, ventilation, awareness to avoid indoor burning
Agriculture	PM, CO, NOx, NH3	No burning enforcement + incentives, in-situ management (mulching, Happy Seeder), ex-situ use (bio-CNG, pellets), balanced fertiliser use
Waste & Landfills	PM, toxic gases	No open burning, segregation at source, composting/biomethanation, landfill gas capture, scientific landfill management
Brick kilns	PM, SO2	Zig-zag technology, cleaner fuels, compliance checks, kiln cluster modernization

📘 FGD (Flue Gas Desulfurization)

A pollution control system used mainly in thermal power plants to remove sulfur dioxide (SO2) from exhaust gases.

📘 Electrostatic Precipitator (ESP)

A device that removes fine particles from exhaust gas using electric charge. Widely used in power plants and industries.

📘 Catalytic Converter

A vehicle device that converts harmful gases like CO and NOx into less harmful substances using catalysts.

8.3 Urban Planning and "Design-based" Solutions

Transit-oriented development: Less dependence on private vehicles.
Green buffers and urban forests: Help as support measures (not a replacement for emission cuts).
Ventilation corridors: Protect natural wind pathways in city design.
Better road design: Reduce dust re-suspension and congestion hotspots.

8.4 Behavioral and Community Measures

Stop open burning of leaves and waste.
Use public transport/carpooling for daily commute.
Maintain vehicles and avoid unnecessary idling.
Adopt clean cooking and ensure ventilation.
Citizen reporting apps and community monitoring can support enforcement.

8.5 Short-term Emergency Measures (During Severe Episodes)

Restrict high-emitting construction and demolition temporarily.
Increase public transport frequency.
Regulate diesel generator use.
Graded actions like those under GRAP (2017) in Delhi-NCR.

Important UPSC point: Emergency steps can reduce peak exposure, but long-term improvement needs steady emission reduction across all sectors.

9) Challenges in Controlling Air Pollution in India

Multi-source nature: Traffic + dust + industry + households + agriculture all contribute.
Inter-state coordination: Pollution travels across districts and states.
Weak enforcement: Standards exist, but monitoring and compliance can be uneven.
Informal sector: Small industries, old vehicles, waste burning are hard to regulate.
Data gaps: Need better emission inventories and regular source apportionment.
Equity issue: Poor households face higher indoor pollution exposure.

10) Way Forward: High-Quality Mains Points

Shift to airshed management: Regional plans for Indo-Gangetic Plain, industrial corridors, and major urban clusters.
Strengthen clean energy transition: Cleaner power reduces SO2, NOx, and PM.
Modernize transport: EV buses, rail-based freight, better last-mile public transport.
Dust management is non-negotiable: Mechanised sweeping, strict construction norms, paved shoulders.
Clean cooking focus: Ensure sustained use of clean fuels, not just connections.
Modern waste systems: Stop open burning through segregation and processing capacity.
Technology + governance together: Devices like ESP/FGD help only if enforced and maintained properly.
Integrate health framing: Make air quality a public health priority with local action and awareness.

11) UPSC PYQs (Themes + Model Approach)

📝 UPSC (Theme) - Delhi Smog and Air Pollution Governance

Approach: Explain multiple sources (transport, dust, biomass burning, industry) + meteorology (inversion) + policy response (GRAP 2017, NCAP 2019, CAQM 2021) + long-term solutions (public transport, dust control, clean energy, clean cooking).

📝 UPSC (Theme) - Crop Residue Burning and Air Quality

Approach: Link agriculture practices to regional airshed pollution; suggest incentives + machinery + market use of residue (bioenergy, pellets) + enforcement + coordination between states.

📝 UPSC (Theme) - AQI, Monitoring, and Policy Effectiveness

Approach: Mention AQI as communication tool; highlight need for emission inventory, continuous monitoring, and strict compliance; show why data must lead to action (sector plans).

📝 UPSC (Theme) - Indoor Air Pollution and Vulnerable Groups

Approach: Explain solid fuel cooking + ventilation issue; highlight women/children exposure; suggest clean cooking fuels, awareness, improved stoves, and public health integration.

📝 UPSC (Theme) - Air Pollution and Climate Co-benefits

Approach: Show how reducing black carbon and fossil fuel combustion improves both health and climate goals; explain that some aerosols cool but still harm health—so focus must be clean air and clean energy together.

12) Practice MCQs (With Answers and Explanations)

PM2.5 is considered more harmful than PM10 mainly because:
- A) It is always produced only by natural sources
- B) It can penetrate deep into lungs and may enter bloodstream
- C) It is heavier and settles quickly
- D) It has no relation with combustion processes
Answer: B) It can penetrate deep into lungs and may enter bloodstream

Explanation: PM2.5 is fine and reaches deep respiratory regions, increasing long-term health risks.
Ground-level ozone (O3) is best described as:
- A) A primary pollutant emitted directly from vehicles
- B) A secondary pollutant formed from NOx and VOCs in sunlight
- C) A pollutant emitted only from coal mines
- D) A pollutant found only indoors
Answer: B) A secondary pollutant formed from NOx and VOCs in sunlight

Explanation: Ozone near ground forms through photochemical reactions involving NOx and VOCs.
Temperature inversion worsens pollution because it:
- A) Increases rainfall that washes pollutants
- B) Traps pollutants near the ground by reducing vertical mixing
- C) Converts PM10 into PM2.5 directly
- D) Stops emissions from sources
Answer: B) Traps pollutants near the ground by reducing vertical mixing

Explanation: In inversion, cold air near surface is trapped below warm air, so pollutants accumulate.
Which one is an example of a non-exhaust emission from vehicles?
- A) Carbon monoxide from tailpipe
- B) Nitrogen dioxide from tailpipe
- C) Brake and tyre wear particles
- D) Sulfur dioxide from coal
Answer: C) Brake and tyre wear particles

Explanation: Non-exhaust sources include brake dust, tyre wear, and re-suspended road dust.
Flue Gas Desulfurization (FGD) is mainly used to control:
- A) Carbon monoxide
- B) Sulfur dioxide
- C) Ground-level ozone
- D) Lead
Answer: B) Sulfur dioxide

Explanation: FGD systems are installed in thermal power plants to remove SO2.
Which set correctly matches pollutant and major sector source in India?
- A) NH3 – mainly from metro rail
- B) SO2 – mainly from coal-based power plants
- C) O3 – directly emitted from construction sites
- D) PM2.5 – only from sea salt
Answer: B) SO2 – mainly from coal-based power plants

Explanation: SO2 is strongly linked to coal combustion; ozone is secondary, and NH3 is linked to agriculture.
NCAP (2019) in India primarily aims to:
- A) Replace the Air Act, 1981
- B) Provide a national framework for city action plans and air quality improvement
- C) Ban all private vehicles immediately
- D) Measure only indoor air pollution
Answer: B) Provide a national framework for city action plans and air quality improvement

Explanation: NCAP focuses on monitoring, city action plans, and coordinated efforts for cleaner air.
Which is the most correct statement about smog in Indian cities?
- A) Smog is only caused by dust, never by gases
- B) Smog severity depends on emissions and meteorology (wind, inversion, humidity)
- C) Smog occurs only during monsoon
- D) Smog has no health impact
Answer: B) Smog severity depends on emissions and meteorology (wind, inversion, humidity)

Explanation: Even with similar emissions, weather conditions can turn pollution into severe smog episodes.
Which control measure is most suitable for construction dust control?
- A) Low-NOx burners
- B) Dust screens, covering materials, and mechanised sweeping
- C) FGD installation
- D) Catalytic converter replacement in cars
Answer: B) Dust screens, covering materials, and mechanised sweeping

Explanation: Construction and road dust require site management and dust suppression steps.
The best long-term strategy to reduce air pollution is:
- A) Only emergency measures during peak days
- B) One single technology solution for all sectors
- C) Steady emission reduction across sectors with strong monitoring and enforcement
- D) Ignoring indoor air pollution
Answer: C) Steady emission reduction across sectors with strong monitoring and enforcement

Explanation: Air pollution is multi-source, so sustained sector-wise emission control is essential.

SEO Toolkit (For clarityupsc.com)

Suggested SEO Title: Air Pollution in India: Types, Sources, Effects & Control Measures (UPSC Notes)

Suggested Slug: environment-upsc-notes/air-pollution-types-sources-control-measures

Focus Keywords: Air Pollution UPSC, PM2.5 PM10, AQI India, NCAP 2019, GRAP 2017, CAQM 2021, Delhi smog, indoor air pollution

Meta Description: Learn air pollution for UPSC with clear notes on types (primary/secondary), sources (transport, industry, dust, biomass), impacts, AQI, and best control measures with India-specific examples and MCQs.