Maarg Manthan · Topic 20.6

Key Activities and Associated Air Pollutants

Environment & Ecology › Protected Areas Lists and Recent Developments in Environment · Topic 20.6

Different human activities release different air pollutants, and linking each activity with its main pollutants is a standard way to understand air quality and design controls. Burning coal in thermal power plants releases sulphur dioxide (SO2), oxides of nitrogen (NOx), particulate matter (PM), carbon dioxide (CO2), mercury and fly ash. Road vehicles emit carbon monoxide (CO), NOx, hydrocarbons, particulate matter and, in diesel engines, black carbon; benzene comes from petrol, and lead, once added to petrol, was phased out in India by 2000 with unleaded fuel. Cement, steel and brick kilns emit particulate matter, CO2 and SO2, while oil refineries and petrochemical plants release SO2, hydrogen sulphide, volatile organic compounds and benzene. Fertiliser plants emit ammonia and fluorides, aluminium smelters emit fluorides, and the chlor-alkali industry can release chlorine and mercury. Agriculture contributes methane from paddy fields and livestock, ammonia from fertilisers and manure, and fine particles from burning crop residue, which also releases CO and black carbon. Cooking with biomass and kerosene in homes emits PM2.5, CO and black carbon. Construction, mining and road dust add coarse particles (PM10), and burning of waste and plastics produces dioxins and furans. Refrigerants and foams are sources of CFCs and HFCs. Landfills and wetlands release methane. Hedge details: the list is indicative, and the share of each source varies by city and study, so check the latest source apportionment studies.

5 min read · UPSC Prelims · Environment & Ecology · Protected Areas Lists and Recent Developments in Environment

At a Glance

Power SO2, NOx, PM, CO2
Vehicles CO, NOx, HC, PM
Farming Methane, ammonia, PM
Households PM2.5, CO
Waste burning Dioxins, furans
Exam link UPSC Prelims, Environment & Ecology: Protected Areas Lists and Recent Developments in Environment

Where Does It Fit?

This topic opens the second half of the macro on lists and special topics and matches activities with pollutants. It supports the later topics on the Air Quality Index and Graded Response Action Plan. Previous topic: List of Sacred Groves and Mangrove Sites in India. Next topic: International Solar Alliance (ISA).

Which Activity Produces Which Pollutant?

Activity	Main air pollutants
Thermal power plants	SO2, NOx, particulate matter, CO2, mercury, fly ash
Road transport	CO, NOx, hydrocarbons, PM, black carbon; benzene from petrol
Cement and steel	Particulate matter, CO2, SO2, CO
Oil refineries	SO2, hydrogen sulphide, VOCs, benzene
Fertilisers	Ammonia, fluorides, oxides of nitrogen
Brick kilns	PM, SO2, CO and black carbon
Agriculture	Methane from paddy and cattle, ammonia, PM from residue burning

What Are the Effects and Controls?

SO2: acid rain and respiratory harm; control by flue gas desulphurisation
NOx: smog, ozone and acid rain; control by catalytic converters and low NOx burners
PM2.5: deep lung penetration and heart disease; control by electrostatic precipitators and clean fuels
CO: reduces oxygen carrying capacity of blood
Ozone: a secondary pollutant formed from NOx and VOCs in sunlight
Methane: a potent greenhouse gas
Black carbon: short-lived warming agent
Dioxins: toxic and persistent; controlled under the Stockholm Convention

What Else Should You Remember?

Primary pollutants: emitted directly from a source
Secondary pollutants: formed in the air, such as ozone and some particles
Criteria pollutants: those with national ambient standards
NAAQS: National Ambient Air Quality Standards of 2009 cover 12 pollutants
NAAQS list: PM10, PM2.5, SO2, NO2, CO, ozone, lead, ammonia, benzene, benzo(a)pyrene, arsenic and nickel
Thermal power: a large source of SO2 and fly ash; emission norms were tightened in 2015
FGD: flue gas desulphurisation units to cut SO2
Bharat Stage norms: vehicle emission standards; BS-VI nationwide from April 2020
Diesel vehicles: emit more NOx and particles
Two-wheelers: significant source of hydrocarbons in cities
Crop residue burning: seasonal source in Punjab, Haryana and western UP
Biomass cooking: household air pollution
Ujjwala: LPG scheme reduces household smoke
Dust: road, construction and demolition dust
Waste burning: open burning of garbage and plastics
Industrial VOCs: solvents and paints
Ammonia: contributes to secondary particles
Methane sources: paddy, ruminants, landfills and fossil fuel leaks
CFCs and HFCs: refrigeration, air conditioning and foams
Mercury: coal burning and chlor-alkali plants; Minamata Convention
Source apportionment: studies by IITs and others measure the share of each source
Seasonal variation: winter inversions trap pollutants in north India
Link to previous: see List of Sacred Groves and Mangrove Sites in India
Link to next: see International Solar Alliance (ISA)
Link to AQI: see National Air Quality Index and Graded Response Action Plan for Air Pollution
Caution: shares of each source vary by city and study
Exam hint: match sources with pollutants and remember the controls
Lead: Leaded petrol was phased out in India by 2000, and lead levels in city air fell sharply
Benzene: Released from petrol vehicles and fuel stations, and a known carcinogen
Ozone: Ground-level ozone rises in summer sun and harms lungs and crops
Health effects: Fine particles are linked with asthma, lung cancer, heart disease and early death, and are the major pollutant in many Indian cities
Indoor air: Cooking smoke and tobacco smoke create indoor exposure, especially for women and children in poor households
Control policy: The National Clean Air Programme aims to cut particulate pollution in many cities and relies on city action plans
Fuel quality: Low-sulphur fuels and ethanol blending help cut emissions from vehicles
Monitoring: Continuous monitoring stations by the CPCB and state boards report levels of major pollutants
Metals in air: Lead, arsenic and nickel are measured as toxic components of particles in the ambient air standards
Acid rain: Sulphur and nitrogen gases dissolve in rain and harm buildings, soils and lakes
Visibility: Fine particles and smog reduce visibility and affect aviation and road safety

Why Does It Matter for the Exam?

Power: SO2, NOx, PM
Vehicles: CO, NOx, HC
Farming: Methane, ammonia
Current affairs link: Stubble burning
Common errors: mixing primary and secondary pollutants

As an analytical point, the same city can have many sources, and controls must target each one. Power and industry need emission norms, transport needs fuel and engine standards, and households and farms need clean fuel and alternatives to burning.

Why Is This Topic Important?

Match Source to pollutant
Control Target each source
Health Particles matter

What Came Next?

The next topic covers the International Solar Alliance. Next topic: International Solar Alliance (ISA).

Key People and Terms

PM2.5 Fine particulate matter
NOx Oxides of nitrogen
VOC Volatile organic compound
NAAQS National ambient air quality standards
FGD Flue gas desulphurisation
BS-VI Bharat Stage VI norms

Exam Corner

Points to Remember

Power: SO2, NOx, PM.
Vehicles: CO, NOx, HC.
Paddy: methane.
Waste burning: dioxins.
BS-VI from 2020.

Do Not Confuse With

Primary and secondary Direct versus formed in air
PM10 and PM2.5 Coarse versus fine particles
CO and CO2 Poisonous gas versus greenhouse gas

Memory Hook

Power burns SO2, cars give CO, paddy gives methane, waste gives dioxin.

Mains Angle

Questions ask for matching sources and pollutants. These points help.

Sources Many
Pollutants Match
Controls Target

A Question You May Face

An original practice question, not a past paper question.

“Discuss the major sources of air pollutants in India and the measures to control them.”

How to Answer

Sources Many.
Pollutants Match.
Effects Health.
Controls Targeted.

GS Relevance

Prelims: matching activities with pollutants. GS Paper 3: air pollution sources and control.

Frequently Asked Questions

What pollutants come from thermal power plants?

Coal-fired thermal power plants release sulphur dioxide, oxides of nitrogen, particulate matter, carbon dioxide, mercury and fly ash. Controls include electrostatic precipitators for particles, flue gas desulphurisation for sulphur dioxide, low NOx burners, and emission norms notified by the Environment Ministry, which were tightened in 2015.

Which pollutants are released by vehicles?

Vehicles emit carbon monoxide, oxides of nitrogen, hydrocarbons, particulate matter and, from diesel engines, black carbon. Petrol vehicles also release benzene. India has moved to Bharat Stage VI norms nationwide from April 2020, and the phase-out of leaded petrol was completed around 2000.

Which activities release methane?

Methane is released from flooded paddy fields, cattle and other ruminants, landfills, wetlands, and leaks in oil, gas and coal operations. It is a potent greenhouse gas with a shorter life in the air than carbon dioxide, so reducing methane can slow near-term warming.

What is the difference between primary and secondary pollutants?

Primary pollutants are emitted directly from sources, such as sulphur dioxide, carbon monoxide and soot. Secondary pollutants form in the atmosphere through reactions, such as ground-level ozone formed from nitrogen oxides and volatile organic compounds in sunlight, and some fine particles formed from ammonia and sulphur or nitrogen gases.

Why is open burning of waste harmful?

Open burning of garbage, plastics and crop residue releases fine particles, carbon monoxide, black carbon and toxic chemicals like dioxins and furans, which can cause respiratory and other diseases and persist in the environment. It also contributes to winter smog in north India and is prohibited under several rules.

PYQ Practice — Statement Analysis

1 Paddy fields are a source of methane.

True

Along with cattle.

2 Ozone is a primary pollutant.

False

It is secondary.

3 Thermal power plants release SO2.