Pollution and Climate Change
Pollution and Climate Change
Pollution is the addition of harmful substances to air, water or soil; climate change is the long-term warming of the Earth caused mainly by greenhouse gases. NTPC asks the cause of acid rain, the gases behind global warming and ozone depletion, diseases caused by pollutants, and which sector emits the most greenhouse gases.
1. Air Pollution
| Pollutant or event | Source and effect |
|---|---|
| Acid rain | Sulphur dioxide and nitrogen oxides dissolve in rain; pH below 5.6; damages the Taj Mahal marble (marble cancer) |
| Carbon monoxide | Incomplete burning; binds haemoglobin and cuts oxygen supply |
| Photochemical smog | Nitrogen oxides and hydrocarbons react in sunlight to form ozone and PAN |
| Classical (London) smog | Smoke and sulphur dioxide in cold, damp air |
| PM2.5 | Fine particles that reach deep into the lungs |
| Bhopal gas tragedy (1984) | Methyl isocyanate leak |
| Ozone layer | In the stratosphere; depleted by CFCs; measured in Dobson units |
2. Water and Soil Pollution
| Pollutant | Disease or effect |
|---|---|
| Mercury | Minamata disease |
| Cadmium | Itai-itai disease |
| Excess fluoride | Fluorosis |
| Arsenic | Skin lesions; groundwater problem in the Ganga plain |
| Nitrate | Blue baby syndrome |
| Fertiliser run-off | Eutrophication: algal bloom, oxygen loss, fish death |
| High BOD | Water heavily polluted with organic waste |
3. Greenhouse Effect and Climate Change
| Item | Fact |
|---|---|
| Main greenhouse gases | Carbon dioxide, methane, nitrous oxide, CFCs, water vapour |
| Methane sources | Paddy fields, livestock, landfills, wetlands |
| Largest emitting sector worldwide | Energy, especially electricity and heat from fossil fuels |
| Effects | Rising temperature and sea level, melting glaciers, extreme weather |
| India's net-zero target | 2070 (announced at COP26, Glasgow) |
| National Clean Air Programme | Launched 2019 to cut particulate pollution in cities |
✗ Acid rain is caused mainly by carbon dioxide | ✓ It is caused mainly by sulphur dioxide and nitrogen oxides
✗ The ozone hole is caused by carbon monoxide | ✓ It is caused mainly by CFCs releasing chlorine in the stratosphere
हिंदी नोट: अम्ल वर्षा मुख्य रूप से सल्फर डाइऑक्साइड और नाइट्रोजन ऑक्साइड के कारण होती है। मिनामाता रोग पारे से और इटाई-इटाई रोग कैडमियम से होता है। ग्रीनहाउस गैसों का सबसे बड़ा उत्सर्जक क्षेत्र ऊर्जा (बिजली और ऊष्मा उत्पादन) है।
Exam Pointer: Verified NTPC patterns: the cause of acid rain (August 2025 UG CBT-1) and the sector that emits the most greenhouse gases (January 2021 CBT-1). Ozone, smog and water-pollution disease questions are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Acid rain
[PYQ: NTPC UG CBT-1 21-Aug-2025 Shift-2]
EXAM LEVEL
Q. Below what pH is rain called acid rain?
Below about 5.6, the pH of normal rain saturated with carbon dioxide.
Answer: 5.6
EXAMATLAS LEVEL
Q. Why is the Taj Mahal said to suffer from "marble cancer", and which gases are mainly responsible?
Acid rain reacts with calcium carbonate in marble and corrodes it. The acid comes mainly from sulphur dioxide and nitrogen oxides released by industries and vehicles nearby.
Answer: Acid rain eating marble; SO₂ and NOₓ
Pattern 2: Greenhouse gases and emitting sectors
[PYQ: NTPC CBT-1 8-Jan-2021 Shift-2]
EXAM LEVEL
Q. Which agricultural activity is a major source of methane?
Flooded paddy (rice) cultivation, along with livestock.
Answer: Paddy cultivation
EXAMATLAS LEVEL
Q. Which sector is the largest emitter of greenhouse gases worldwide, and by which year does India aim to reach net-zero emissions?
The energy sector, mainly electricity and heat produced by burning fossil fuels. India aims for net zero by 2070.
Answer: Energy sector; 2070
Pattern 3: Ozone depletion and smog
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. In which layer of the atmosphere is the ozone layer found, and in what unit is its thickness measured?
The stratosphere; it is measured in Dobson units.
Answer: Stratosphere; Dobson units
EXAMATLAS LEVEL
Q. Which gases form photochemical smog, and what extra condition does it need?
Nitrogen oxides and hydrocarbons, which react in strong sunlight to form ozone and PAN.
Answer: NOₓ and hydrocarbons; sunlight
Pattern 4: Diseases from pollutants
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Minamata disease is caused by which metal?
Mercury.
Answer: Mercury
EXAMATLAS LEVEL
Q. Match the pollutant with its effect: cadmium, nitrate in drinking water, excess fluoride.
Cadmium causes itai-itai disease, nitrate causes blue baby syndrome and excess fluoride causes fluorosis.
Answer: Itai-itai, blue baby syndrome, fluorosis
60-Second Revision
- Acid rain: SO₂ and NOₓ, pH below 5.6.
- Ozone layer: stratosphere, Dobson units, destroyed by CFCs.
- Minamata mercury; itai-itai cadmium; blue baby nitrate; fluorosis fluoride.
- Largest emitter: energy sector; India net zero by 2070.