This lesson explains environmental pollution, greenhouse gases, acid rain, water purification, and how chemistry helps solve global environmental problems.

1. Core Concepts (Short Notes)

24.1 Pollution

Pollution is the introduction of harmful substances into the environment. Major types:

• Air pollution

• Water pollution

• Soil pollution

• Noise pollution

24.2 Air Pollutants

Common air pollutants:

• CO (Carbon monoxide): produced from incomplete combustion; toxic.

• SO₂ (Sulfur dioxide): from burning fossil fuels; causes acid rain.

• NOx (Nitrogen oxides): from vehicle engines; causes acid rain & smog.

• CO₂: greenhouse gas → global warming.

• Particulates: dust, soot.

24.3 Greenhouse Effect & Global Warming

Greenhouse gases trap heat in the atmosphere:

• CO₂

• CH₄ (methane)

• N₂O

• Water vapor

Effects:

• Rising sea levels

• Extreme weather

• Climate change

24.4 Acid Rain

Caused by SO₂ and NOx reacting with water:

• SO₂ + O₂ + H₂O → H₂SO₄

• NO₂ + H₂O → HNO₃

Effects:

• Damages buildings & monuments

• Kills fish & aquatic life

• Harms plants & soil

24.5 Ozone Layer & Ozone Depletion

Ozone (O₃) absorbs harmful UV radiation. CFCs (chlorofluorocarbons) break down ozone: CFCl₃ → Cl· radical → destroys O₃

Effects:

• Skin cancer

• Cataracts

• Damage to marine life

24.6 Water Pollution

Sources:

• Industrial waste

• Sewage

• Agricultural runoff (fertilizers, pesticides)

• Oil spills

Effects:

• Eutrophication

• Loss of biodiversity

• Unsafe drinking water

24.7 Water Purification Methods

• Sedimentation

• Filtration

• Chlorination

• Aeration

• Reverse osmosis

24.8 Waste Treatment

Primary treatment:

• Screening & sedimentation

Secondary treatment:

• Biological oxidation of organic matter

Tertiary treatment:

• Advanced removal of nutrients (N, P)

• Disinfection

2. Key Reactions & Processes to Remember

Formation of Acid Rain

SO₂ + H₂O → H₂SO₃ → H₂SO₄ NO₂ + H₂O → HNO₃

Ozone Formation & Breakdown

O₂ → 2O (UV) O + O₂ → O₃

CFC breakdown: CFCl₃ → CFCl₂· + Cl· Cl· + O₃ → ClO· + O₂

3. Tips & Tricks for Exams

• Distinguish between greenhouse effect (natural & necessary) vs. enhanced greenhouse effect (caused by humans).

• Acid rain always involves SO₂ or NOx.

• CFCs are responsible for ozone depletion—not CO₂.

• Eutrophication occurs due to excess nutrients (N, P).

• Sustainable practices often appear in essay-style questions.

4. Important Points to Remember

• Environmental issues are interconnected.

• Chemistry provides solutions: catalytic converters, scrubbers, biodegradable materials.

• Clean energy reduces pollution and global warming.

• Water treatment is essential for public health.

International agreements (e.g., Montreal Protocol) help reduce ozone depletion.