Chapter 7 – Environmental Chemistry (JEE)
1. Introduction to Environmental Chemistry
Environmental Chemistry deals with the study of chemical processes occurring in the environment,
their effects on living organisms, and methods to control environmental pollution.
This chapter is mainly **theoretical** but very **scoring** in JEE Main.
2. Atmospheric Pollution
Atmospheric pollution is the presence of undesirable substances in air that adversely affect
human health, plants, animals, and materials.
Major Air Pollutants
- Carbon monoxide (CO)
- Oxides of nitrogen (NO, NO₂)
- Oxides of sulphur (SO₂, SO₃)
- Hydrocarbons
- Particulate matter (PM₂.₅, PM₁₀)
3. Carbon Monoxide Pollution
Carbon monoxide is produced by incomplete combustion of carbon-containing fuels.
$2C + O_2 \rightarrow 2CO$
CO binds strongly with haemoglobin to form carboxyhaemoglobin, reducing oxygen transport.
4. Oxides of Nitrogen (NOx)
Oxides of nitrogen are produced during high-temperature combustion in automobile engines.
$N_2 + O_2 \xrightarrow{high\ temperature} 2NO$
$2NO + O_2 \rightarrow 2NO_2$
5. Oxides of Sulphur (SOx)
SO₂ is produced by burning fossil fuels containing sulphur.
$S + O_2 \rightarrow SO_2$
$2SO_2 + O_2 \rightarrow 2SO_3$
6. Acid Rain
Acid rain refers to precipitation with pH less than 5.6 due to formation of strong acids.
$SO_3 + H_2O \rightarrow H_2SO_4$
$4NO_2 + 2H_2O + O_2 \rightarrow 4HNO_3$
Effects include soil degradation, corrosion of monuments, and aquatic life damage.
7. Smog
Classical Smog
Occurs in cold, humid climates and contains smoke + fog (London smog).
Photochemical Smog
Occurs in warm, dry climates due to sunlight acting on NO₂ and hydrocarbons.
$NO_2 \xrightarrow{sunlight} NO + O$
$O + O_2 \rightarrow O_3$
8. Tropospheric Ozone
Ozone at ground level is a harmful secondary pollutant.
It causes eye irritation, respiratory problems, and damages crops.
9. Greenhouse Effect
Greenhouse gases trap infrared radiation, increasing Earth's temperature.
Major Greenhouse Gases
- CO₂
- CH₄
- N₂O
- Water vapour
- CFCs
10. Global Warming
Global warming is the gradual increase in Earth's average temperature due to enhanced greenhouse effect.
Consequences include melting glaciers, sea-level rise, and climate change.
11. Ozone Layer
The ozone layer in the stratosphere protects Earth from harmful UV radiation.
$O_2 \xrightarrow{UV} 2O$
$O + O_2 \rightarrow O_3$
12. Ozone Depletion
Chlorofluorocarbons (CFCs) are responsible for ozone depletion.
$CF_2Cl_2 \xrightarrow{UV} CF_2Cl + Cl$
$Cl + O_3 \rightarrow ClO + O_2$
One chlorine radical can destroy thousands of ozone molecules.
13. Water Pollution
Water pollution occurs due to contamination of water bodies by harmful substances.
Sources
- Industrial waste
- Sewage
- Agricultural runoff
14. Chemical Oxygen Demand (COD)
COD is the amount of oxygen required to oxidize organic matter chemically.
Higher COD indicates higher water pollution.
15. Biochemical Oxygen Demand (BOD)
BOD is the amount of oxygen required by microorganisms to decompose organic matter biologically.
High BOD leads to depletion of dissolved oxygen in water.
16. Soil Pollution
Soil pollution occurs due to excessive use of pesticides, fertilizers, and industrial waste.
17. Industrial Waste Management
Methods include recycling, treatment before discharge, and use of eco-friendly technologies.
18. Green Chemistry
Green chemistry aims to reduce or eliminate hazardous substances in chemical processes.
Key Principles
- Use of safer solvents
- Waste prevention
- Energy efficiency
19. Environmental Laws and Protocols
Important agreements include:
- Montreal Protocol (ozone protection)
- Kyoto Protocol (greenhouse gas reduction)
20. Importance of Environmental Chemistry
Understanding environmental chemistry helps in sustainable development and pollution control.
This chapter connects chemistry with real-life environmental issues.