Environmental Chemistry 

1) Basic Definitions

• Pollutant: Any substance present in the environment in harmful concentration.
• Environmental pollution: Contamination of environment due to harmful wastes, mainly from human activities.

2) Atmospheric Regions

• Troposphere: Up to ~10 km from sea level.
• Stratosphere: Between 10 km and 50 km.

3) Types of Atmospheric Pollution

• Tropospheric pollution
• Stratospheric pollution
• Tropospheric pollutants may be gaseous or particulate.

4) Gaseous Air Pollutants

Oxides of Sulphur (SO₂, SO₃)

• SO₂ is the major pollutant.
• Causes eye irritation, redness and tears.
• Major contributor to acid rain.

Oxides of Nitrogen (NO, NO₂)

• Formed at high temperature (>1210°C) or during lightning.
• NO is oxidised by ozone to NO₂.
• NO₂ is highly toxic and responsible for acid rain.

Oxides of Carbon

• Carbon monoxide (CO): Produced by incomplete combustion.
• CO binds with haemoglobin more strongly than oxygen.
• Causes dizziness, muscular weakness, mental impairment and death.
• Carbon dioxide (CO₂): Natural constituent; essential for plants.
• Excess CO₂ causes respiratory stimulation and asphyxiation.

5) Greenhouse Effect

• Phenomenon where atmospheric gases trap heat radiated from Earth.
• Greenhouse gases: CO₂, CH₄, O₃, CFCs.
• Leads to global warming and rise in average temperature.
• Increases incidence of diseases like malaria, dengue and yellow fever.

6) Particulate Pollutants

Visible Particulates

• Living organisms like bacteria, fungi and moulds.
• Fungi can cause plant diseases.

Non-Visible Particulates

• Formed by breakdown of larger particles or condensation.
• Long-term exposure causes lung fibrosis.
• Industrial lung disease is called Pneumoconiosis.

7) Smog

Classical Smog

• Occurs in cool, humid climate.
• Caused by SO₂ and particulate matter.

Photochemical Smog

• Occurs in warm, dry and sunny climate.
• Caused by sunlight acting on NOx and hydrocarbons.
• Main components: NOx, O₃, PAN (Peroxyacetyl nitrate).
• PAN is most toxic — damages plant leaves.

8) Water Pollution Parameters

Biochemical Oxygen Demand (BOD)

• Amount of dissolved oxygen required by microorganisms.
• Measures organic pollution in water.
• Higher BOD → more polluted water.

Chemical Oxygen Demand (COD)

• Water treated with K₂Cr₂O₇ in acidic medium.
• Measures oxygen required to oxidise pollutants chemically.
• Expressed in ppm of oxygen.