Air Pollution

Introduction

To understand air pollution, imagine the atmosphere as a delicate mixture of gases that sustains life. When any unwanted solid, liquid or gaseous substance enters this mixture in harmful concentrations, it disrupts natural processes.

This disruption—whether it affects humans, animals, plants, property, or natural cycles—is what we call air pollution.

Why Is Air Pollution Increasing?

The common thread across power plants, industries, transport, mining, construction, and stone-quarrying is the burning of fossil fuels. As India urbanises and industrialises, fossil fuel usage keeps climbing—so does air pollution.

Acid Rain

Fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels burn, they release:
→ Nitrogen oxides (NOx)
→ Sulphur oxides (SOx)

These gases react with atmospheric water vapour to form:
→ Sulphuric acid (H₂SO₄)
→ Nitric acid (HNO₃)

When these acids fall along with rainwater, the rain becomes acidic.
This is called acid rain.

Marble Cancer

Acid rain corrodes marble monuments such as the Taj Mahal.
This slow corrosion is called marble cancer—a term often asked in UPSC prelims.

CFCs and Ozone Layer Depletion

Chlorofluorocarbons (CFCs) were widely used in refrigerators, air conditioners, aerosol sprays.

CFCs are extremely stable, so they reach the stratosphere where sunlight breaks them down, releasing chlorine radicals that destroy the ozone layer.

This leads to increased UV radiation reaching the earth, harming life forms.

Smog — A Sign of Severe Pollution

When fossil fuels burn, they produce unburnt carbon particles, hydrocarbons, other suspended particulate matter (SPM).

In cold weather, when water vapour condenses, it binds with these particles and creates a thick, hazy layer called smog.
Smog reduces visibility and is a clear indicator of poor air quality.

Major Causes of Air Pollution

1. Vehicular and Industrial Emissions (The Biggest Source in Cities)

Vehicles release a cocktail of pollutants. More than 80% of vehicular pollution comes from:
→ Carbon monoxide (CO)
→ Oxides of Nitrogen (NOx)
→ Non-Methane Volatile Organic Compounds (NMVOCs)
(examples: benzene, ethanol, formaldehyde, cyclohexane, acetone)

Other pollutants include:

• Methane (CH₄)
• Carbon dioxide (CO₂)
• Oxides of sulphur (SOx)
• Total Suspended Particles (TSPs)

Industries like iron–steel, cement, fertiliser, aluminium, sugar, and paper further add:
→ SPM
→ SOx,
→ NOx, and
→ CO₂.

2. Improper Use of Pyrolysis

What is pyrolysis?

Pyrolysis is the breakdown of synthetic material at high temperatures (300–400°C) in the absence of oxygen.

It is safer than open burning, but crude or sub-optimal pyrolysis technologies leave behind
→ fine carbon matter,
→ pyro-gas,
→ pyro-oil
which can pollute the local environment.

Applications

• Producing methanol, activated carbon, charcoal
• Producing synthetic gas for electricity generation
• Converting mixed pyrolytic waste into building materials
• Recently proposed for converting COVID-19 PPE kits into bio-crude fuel

Advantages

• Can process a wide range of waste cheaply
• Reduces landfill burden and greenhouse gases
• Minimises water pollution

Because of the pollution caused by burning tyres, the National Green Tribunal (2014) banned:
→ open burning of used tyres,
→ their use as fuel in brick kilns.

3. Fuel Adulteration

Kerosene is taxed less because it is a cooking fuel for poorer households.
This price difference encourages the illegal mixing of kerosene into petrol or diesel.

Adulterated fuel increases emissions of:
→ CO,
→ NOx,
→ particulate matter.

This especially worsens pollution in urban areas with high vehicle density.

4. Emissions from Agriculture, Waste Treatment, and Biomass Burning

Agriculture releases:

• Ammonia (NH₃)
• Methane (CH₄)
• Nitrous oxide (N₂O) — a strong greenhouse gas

Landfills and wastewater treatment plants also emit methane.
Composting generates ammonia, contributing to local air pollution.

5. Stubble Burning — A Seasonal but Severe Crisis

Stubble burning is the deliberate burning of crop residue after harvesting paddy or wheat. While it occurs across India, Punjab, Haryana, and Uttar Pradesh are the major contributors to the NCR winter pollution crisis.

Why does it spike in October–November?

There is only a narrow 2–3 week window between paddy harvesting and sowing of the Rabi crop. Farmers use burning as the quickest and cheapest clearance method.

Even though:

• it is a crime under IPC and the Air (Prevention and Control of Pollution) Act, 1981,
• and the NGT has banned stubble burning in several states,

the practice continues because alternatives are costly or inaccessible.

Effects of Stubble Burning

a. Pollution

Releases large amounts of:
→ CH₄,
→ CO,
→ VOCs,
leading to smog and respiratory problems.

b. Loss of Soil Fertility

Destroys beneficial microbes, nitrogen-fixing bacteria, organic carbon.

c. Loss of Soil Moisture

Heat penetrates the upper layers of soil, evaporating moisture and reducing productivity.

6. Household (Indoor) Air Pollution

Indoor pollution often goes unnoticed but is extremely harmful.

Sources

Burning coal, wood, agricultural residue, animal dung, kerosene under poorly ventilated conditions leads to emissions of:
→ PM2.5,
→ black carbon,
→ CO₂,
→ CO,
→ CH₄.

Even paints, carpets, furniture release VOCs (volatile organic compounds).

This disproportionately affects women and children in rural India.

7. Volcanism and Air Pollution

Volcanoes release gases like:
→ SO₂,
→ CO₂,
→ hydrogen fluoride,
→ hydrogen sulphide.

Local Effects

SO₂ leads to:
→ acid rain,
→ air pollution in downwind regions.

Global Effects

Large explosive eruptions inject sulphur aerosols into the stratosphere, which:
→ reduce surface temperatures (temporary global cooling)
→ contribute to ozone layer depletion

This is why volcanic eruptions have both short-term climatic impacts and long-term atmospheric effects.

World Air Quality Report 2024

The World Air Quality Report 2024, released by Swiss company IQAir, ranked India as the 5th most polluted country globally. 

What are the Key Findings of the World Air Quality Report? 

India

• India is the 5th most polluted country in 2024, improving slightly from 3rd place in 2023. 
• Polluted Cities: Delhi remains the most polluted capital globally with a Particulate matter (PM) 2.5 concentration of 91.6 µg/m³ (micrograms per cubic metre).
  • 6 of the world’s 10 most polluted cities and 13 of the top 20 are in India, with Byrnihat (Assam-Meghalaya border) topping the list at a PM2.5 concentration of 128.2 µg/m³.  
  • Other polluted cities include Mullanpur (Punjab), Gurugram, Faridabad, Bhiwadi, and Noida. 
• PM2.5 Reduction: India saw a 7% decrease in PM2.5 levels, averaging 50.6 µg/m³ in 2024, down from 54.4 µg/m³ in 2023.
  • However, this is still 10 times higher than the World Health Organization (WHO’s) recommended safe limit of 5 µg/m³. 35% of Indian cities reported PM2.5 levels exceeding this limit. 
• Pollution Sources: Major contributors include vehicle emissions, industrial pollution, and the burning of biomass.
  • Northern India faced extreme pollution levels with crop stubble-burning contributing to 60% of PM2.5 levels. 

Global

The most polluted countries by annual average PM2.5 levels are Chad (91.8 µg/m³), Bangladesh (78 µg/m³), Pakistan (73.7 µg/m³), and Congo (58.2 µg/m³). 

• The report highlights that most of the global population is breathing polluted air, with only 12 countries, regions, or territories reporting PM2.5 concentrations below the WHO’s recommended limit.