🌍 Chemistry — Environmental Chemistry
1. Environment
COMPONENTS OF ENVIRONMENT
- Abiotic (Non-living): Atmosphere, Hydrosphere, Lithosphere
- Biotic (Living): Plants, Animals, Microorganisms
- Energy components: Solar radiation, thermal energy
LAYERS OF ATMOSPHERE
- Troposphere: Lowest layer (up to 18 km); contains N₂, O₂, CO₂, water vapour
- Stratosphere: 18-60 km; contains ozone layer (20-40 km); temperature rises with altitude
- Mesosphere: 60-85 km; temperature decreases; meteors burn here
- Thermosphere: 85-640 km; temperature up to 1500°C; International Space Station orbits here
- Exosphere: 500-1600 km; contains ionised gases; merges into interstellar space
OZONE FORMATION
- O₂ + UV → 2O
- O + O₂ → O₃
- Ozone absorbs 99.5% of harmful UV radiation
2. Atmospheric Pollution
POLLUTANTS
- Primary pollutants: Emitted directly (SO₂, NO₂, CO)
- Secondary pollutants: Formed by reactions (PAN, O₃, Aldehydes)
MAJOR GASEOUS POLLUTANTS
- SO₂: Causes respiratory diseases, acid rain, damages marble (Taj Mahal)
- NO₂: Brown gas; causes smog, acid rain; affects liver and kidneys
- CO: Forms carboxyhaemoglobin (200x more stable than oxyhaemoglobin); causes asphyxia
- Hydrocarbons: Carcinogenic; react with NOx to form secondary pollutants
PARTICULATE POLLUTANTS
| Disease | Cause |
|---|---|
| Pneumoconiosis | Coal dust inhalation |
| Silicosis | Free silica (SiO₂) inhalation |
| Black lung disease | Coal mine workers |
| Byssinosis | Cotton fibre dust |
3. Smog
CLASSICAL SMOG
- Occurs in cool, humid climate
- Main components: SO₂ + particulate matter
- Chemically reducing in nature
PHOTOCHEMICAL SMOG
- Occurs in warm, dry, sunny climate
- Components: NOx + CO + O₃ + PAN + Aldehydes
- Chemically oxidising in nature
- PAN: Most toxic to plants; causes bronzing of leaves
- Ozone: Pungent smell; damages rubber
- Control: Catalytic converters in vehicles
4. Stratospheric Pollution
OZONE DEPLETION
- Caused by Chlorofluorocarbons (CFCs)
- CFCs used in: Refrigeration, fire extinguishers, aerosol sprayers, plastic foam, electronic cleaning
- One Cl atom destroys 1000 ozone molecules
- Ozone hole: Mainly observed over Antarctica
- Occurs during spring time; gets replenished after spring
EFFECTS OF OZONE DEPLETION
- Skin cancer and cataract in humans
- Reduction of planktons in ocean
- Depletion of plants
5. Acid Rain and Global Warming
ACID RAIN
- Caused by: SO₂ + NO₂ → H₂SO₄ + HNO₃ in rainwater
- Damages: Marble monuments (Taj Mahal), buildings, statues
- Dissolves heavy metals (Pb, Cu, Hg, Al) — enters water sources
- Marble cancer: Corrosion of marble by acid rain
GREENHOUSE EFFECT & GLOBAL WARMING
- Greenhouse gases: CO₂, CH₄, H₂O vapour, N₂O, CFCs
- CO₂ absorbs infrared radiation
- Global warming effects: Melting ice caps, rising sea levels
- Kyoto Protocol: International agreement to reduce greenhouse gases
6. Water Pollution
POLLUTANTS
- Pathogens: Bacteria, viruses
- Organic wastes: Leaves, grass, sewage
- Chemical pollutants: Metals, petroleum, industrial wastes
BOD & COD
- BOD (Biochemical Oxygen Demand): Oxygen required by microbes to decompose organic matter
- COD (Chemical Oxygen Demand): Oxygen consumed by pollutants
- Clean water: BOD < 5 ppm
- Highly polluted water: BOD > 17 ppm
- For healthy aquatic life: DO = 5-6 ppm
WATER POLLUTANTS IN INDIA
- Arsenic: West Bengal, Haryana
- Fluoride: Andhra Pradesh, Gujarat, Haryana, Odisha, Punjab
- Uranium: Punjab
- Ganga Action Plan: Launched in 1985
7. Soil Pollution
SOURCES
- Pesticides: Insecticides (DDT, BHC), Herbicides, Fungicides
- Fertilisers: Excessive use destroys fertility
- Solid wastes: Industrial, farm, radioactive waste
- Soil conditioners: Compounds of As, Hg, Pb
TYPES OF POLLUTION
- Positive soil pollution: Reduced productivity due to undesirable substances
- Negative soil pollution: Reduced productivity due to erosion and overuse
- Landscape pollution: Fertile land to barren due to waste dumping
8. Pollution Control
STRATEGIES
- Recycling: Scrap metal, combustible waste energy recovery
- Sewage treatment: Treatment before discharge
- Incineration: Burning at >1000°C in excess oxygen
- Biogas production: From biodegradable waste
- Oil Zapping: Bioremediation using bacteria for oil spills
GREEN CHEMISTRY
- Reduces/eliminates use and generation of hazardous substances
- Example 1: CO₂ as blowing agent for polystyrene foam (reduces CFCs)
- Example 2: "Sea-nine" — safer marine antifouling compound
ELECTRONIC WASTE (E-WASTE)
- Discarded computers, mobile phones, TVs, refrigerators
- Toxic substances: Dioxins, PCBs, Cadmium, Chromium, Mercury, Lead
- A typical monitor contains >6% lead by weight
Summary: Environmental Chemistry at a Glance
| Topic | Key Point |
|---|---|
| Troposphere | Lowest layer; contains air, water vapour |
| Stratosphere | Contains ozone layer (20-40 km) |
| SO₂ | Causes acid rain, respiratory diseases |
| CO | Forms carboxyhaemoglobin (200x stable) |
| Photochemical Smog | NOx + O₃ + PAN; oxidising |
| CFCs | Ozone depletion; 1 Cl → 1000 O₃ |
| Greenhouse Gases | CO₂, CH₄, H₂O vapour, N₂O, CFCs |
| BOD | Clean water < 5 ppm; polluted > 17 ppm |
KEY TAKEAWAYS FOR UPSC
- Atmosphere layers: Troposphere → Stratosphere → Mesosphere → Thermosphere → Exosphere
- Ozone layer: In stratosphere (20-40 km); absorbs 99.5% UV
- SO₂: Causes acid rain; damages Taj Mahal (marble cancer)
- CO poisoning: Carboxyhaemoglobin 200x more stable than oxyhaemoglobin
- Photochemical smog: Oxidising; contains PAN, O₃, NOx
- CFCs: Deplete ozone; 1 Cl destroys 1000 O₃ molecules
- Greenhouse gases: CO₂, CH₄, H₂O vapour, N₂O, CFCs
- BOD: Clean water < 5 ppm; Highly polluted > 17 ppm
- Water pollutants in India: Arsenic (WB), Fluoride (AP, Gujarat), Uranium (Punjab)
- E-waste: Contains Pb, Cd, Cr, Hg, PCBs
High-Yield Interactive UPSC Quiz (Chemistry — Environmental Chemistry)
Q1. In which layer of the atmosphere is the ozone layer found?
Correct Answer: B. The ozone layer is located in the stratosphere at an altitude of 20-40 km.
Q2. Which gas forms carboxyhaemoglobin with haemoglobin?
Correct Answer: B. Carbon monoxide forms carboxyhaemoglobin, which is 200 times more stable than oxyhaemoglobin.
Q3. How many ozone molecules can one chlorine atom destroy?
Correct Answer: C. One chlorine atom can destroy approximately 1000 ozone molecules.
Q4. Photochemical smog is chemically:
Correct Answer: B. Photochemical smog is chemically oxidising in nature.
Q5. What is the BOD value of clean water?
Correct Answer: B. Clean water has BOD less than 5 ppm, while highly polluted water has BOD more than 17 ppm.
Q6. Which pollutant is responsible for marble cancer at Taj Mahal?
Correct Answer: B. SO₂ causes acid rain, which corrodes the marble of the Taj Mahal (marble cancer).
Q7. Which of the following is NOT a greenhouse gas?
Correct Answer: D. Oxygen (O₂) is not a greenhouse gas. Greenhouse gases include CO₂, CH₄, H₂O vapour, N₂O, and CFCs.
Q8. The Ganga Action Plan was launched in which year?
Correct Answer: C. The Ganga Action Plan was launched in 1985 to reduce pollution levels in the river.
Q9. Which disease is caused by inhalation of free silica?
Correct Answer: B. Silicosis is caused by inhalation of free silica (SiO₂).
Q10. The ozone hole is mainly observed over which region?
Correct Answer: B. The ozone hole is mainly observed over Antarctica during springtime.