60-second revision
- Original six Kyoto gases: CO2, CH4, N2O, HFCs, PFCs, SF6 (NF3 was added in 2012); water vapour is the most abundant natural greenhouse gas.
- Methane sources: flooded paddy, livestock, landfills, wetlands.
- Ozone layer is measured in Dobson units; CFCs are the main culprits; the hole forms over Antarctica in spring.
- Acid rain: SO2 and NOx; pH below ~5.6.
- Minamata – mercury; itai-itai – cadmium; blue baby – nitrates; fluorosis – fluoride.
- High BOD = more organic pollution; eutrophication = nitrate and phosphate overload.
- Bhopal 1984 = methyl isocyanate (MIC) from the Union Carbide plant.
Greenhouse effect and global warming
The Earth's surface absorbs sunlight and radiates heat as infrared radiation. Greenhouse gases absorb part of this outgoing heat and re-radiate it, keeping the planet warm enough for life — the natural greenhouse effect. Human activities, chiefly burning fossil fuels and deforestation, have raised the concentrations of these gases, causing an enhanced greenhouse effect and global warming.
| Gas | Main sources |
|---|---|
| Carbon dioxide (CO2) | Burning coal, oil and gas; deforestation; cement |
| Methane (CH4) | Flooded paddy fields, livestock (enteric fermentation), landfills, wetlands, coal mines |
| Nitrous oxide (N2O) | Nitrogen fertilisers, industrial processes |
| HFCs, PFCs, SF6 | Refrigeration, aluminium smelting, electrical switchgear — very high warming potential |
| Water vapour | Most abundant natural greenhouse gas; rises as air warms (a feedback) |
Effects of warming include melting glaciers and ice sheets, sea-level rise, more intense heatwaves and heavy rainfall events, coral bleaching and shifts in species ranges. Responses are mitigation (cutting emissions, renewable energy, carbon sinks such as forests) and adaptation (heat action plans, drought-resistant crops, coastal protection).
Ozone depletion
Stratospheric ozone absorbs harmful ultraviolet (UV-B) radiation. Chlorofluorocarbons (CFCs) from old refrigerators, aerosol sprays and foams, along with halons and other substances, release chlorine and bromine atoms that destroy ozone. The 'ozone hole' forms over Antarctica every southern spring (September–October), helped by polar stratospheric clouds. Ozone thickness is measured in Dobson units. Note that ozone near the ground is a harmful pollutant, a key part of photochemical smog.
Air pollution
| Issue | Key facts |
|---|---|
| Primary vs secondary pollutants | Primary are emitted directly (CO, SO2, NOx, particulates, lead); secondary form in the air (ground-level ozone, PAN, sulphuric acid) |
| Acid rain | SO2 and NOx form acids; rain below pH ~5.6; damages forests, lakes and marble (the Taj Mahal's 'marble cancer') |
| Classical (London) smog | Smoke plus fog plus SO2; cold, damp conditions |
| Photochemical (Los Angeles) smog | Sunlight acting on NOx and hydrocarbons from vehicles; forms ozone and PAN |
| Particulate matter | PM10 and the finer PM2.5, which penetrates deep into the lungs |
| National Air Quality Index | Covers eight pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3 and lead |
Water and soil pollution
| Pollutant | Disease / effect |
|---|---|
| Mercury | Minamata disease (Japan); nerve damage |
| Cadmium | Itai-itai disease; painful bone damage |
| Nitrates | Blue baby syndrome (methaemoglobinaemia) |
| Fluoride (excess) | Dental and skeletal fluorosis |
| Arsenic | Skin lesions and cancer; groundwater of the Ganga–Brahmaputra delta |
| Lead | Damage to the brain and nervous system, especially in children |
Biochemical Oxygen Demand (BOD) is the amount of oxygen needed by microbes to decompose the organic matter in water — the higher the BOD, the more polluted the water. Eutrophication occurs when nitrates and phosphates from fertilisers and sewage enrich a water body; algal blooms grow, die and decompose, using up dissolved oxygen so fish die. Thermal pollution from power plants also reduces dissolved oxygen.
Waste, noise and disasters
- Solid waste includes municipal waste, plastics, e-waste (old electronics with lead, mercury and cadmium), biomedical waste and fly ash from thermal power plants (which can be used in bricks and cement).
- Bioremediation uses microbes or plants to clean polluted soil and water, e.g. oil-eating bacteria at spill sites.
- Noise is measured in decibels (dB); long exposure to sound above about 85 dB can damage hearing.
- Bhopal gas tragedy (2–3 December 1984): methyl isocyanate leaked from the Union Carbide pesticide plant, among the world's worst industrial disasters.
- Chernobyl (1986, then USSR, now Ukraine) and Fukushima (2011, Japan) were major nuclear accidents.
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