ICSE Class 10 Chemistry: Atmospheric Pollution — Notes 2026

Composition of Clean Atmosphere

• N₂ (78%), O₂ (21%), Ar (0.93%), CO₂ (0.04%), water vapour + trace gases
• Layers: troposphere, stratosphere (ozone layer), mesosphere, thermosphere
• Natural processes maintaining balance: photosynthesis, nitrogen cycle, water cycle

Air Pollutants — Sources and Effects

• CO: incomplete combustion; binds haemoglobin; causes suffocation
• SO₂ from burning coal; irritates respiratory system; causes acid rain
• NOₓ from vehicle exhausts and lightning; photochemical smog precursor

Acid Rain

• Formation: SO₂/NO₂ + H₂O → H₂SO₄/HNO₃; pH < 5.6
• Effects: acidification of lakes (kills fish), leaching of soil nutrients, corrosion of stone buildings (Taj Mahal)
• Control: use low-sulfur fuels, scrubbers in chimneys, catalytic converters

Greenhouse Effect and Global Warming

• Greenhouse gases: CO₂, CH₄, N₂O, water vapour; trap outgoing IR radiation
• Enhanced greenhouse effect due to increased CO₂ from fossil fuels and deforestation
• Consequences: rising sea levels, extreme weather, ecosystem disruption

Ozone Layer Depletion

• Ozone O₃ in stratosphere absorbs harmful UV radiation (UV-B and UV-C)
• CFCs (chlorofluorocarbons) released Cl radicals that catalytically destroy ozone: Cl + O₃ → ClO + O₂
• Montreal Protocol 1987 banned CFCs; ozone hole over Antarctica slowly healing

Water Pollution

• Sewage, agricultural runoff (fertilisers, pesticides), industrial effluents
• Eutrophication: excess nutrients → algal bloom → oxygen depletion → fish death
• Heavy metals (Pb, Hg, Cd) bioaccumulate through food chains

Measures to Reduce Pollution

• Renewable energy (solar, wind) reduces fossil fuel burning
• Catalytic converters in vehicles convert CO, NOₓ, HC to CO₂, N₂, H₂O
• Waste management: reduce, reuse, recycle; ban on single-use plastics