The Atmosphere

Definition: Envelope of different gases around the Earth.

Composition: Nitrogen (78%), Oxygen (21%), Argon (0.9%), CO₂ (0.03%).

Layers:

• Troposphere (0-12 km): Temperature decreases from 17°C to -58°C. Contains 99% of atmospheric mass (N₂, O₂). Weather occurs here. Aircrafts fly here.
• Stratosphere (12-50 km): Temperature increases from -58°C to 2°C due to Ozone layer (absorbs UV). Divided into lower, middle (ozone formation), and upper layers.
• Mesosphere (50-85 km): Temperature decreases to -93°C.
• Thermosphere (85-120 km): Temperature increases.

Definition: Harmful substances in air that damage environment and human health.

Types:

• Primary Pollutants: Emitted directly (e.g., SO₂, SO₃, CO, CO₂, NO, NO₂, CH₄, NH₃). Sources: Fossil fuel combustion, volcanic eruptions.
• Secondary Pollutants: Formed by reactions of primary pollutants (e.g., H₂SO₄, H₂CO₃, HNO₃, HF, PAN - Peroxy Acetyl Nitrate).

Sources:

• Oxides of Carbon (CO, CO₂): Burning of fossil fuels, forest fires. CO is highly poisonous (binds to hemoglobin). CO₂ is a Greenhouse gas.
• Oxides of Sulphur (SO₂, SO₃): Volcanic gases, burning coal/petroleum. Causes acid rain.
• Oxides of Nitrogen (NO_x): Internal combustion engines, thermal power plants. Combines with moisture to form Acid Rain.

Greenhouse Effect: Trapping of heat (Infrared radiations) by CO₂ and water vapors in the atmosphere, keeping Earth warm. CO₂ acts like glass of a greenhouse.

Global Warming: Increase in Earth's average temperature due to increased concentration of CO₂ (Greenhouse gas). Effects: Melting glaciers/snow caps, rising sea levels (floods), extreme weather changes.

Formation: SO₂ and NO_x dissolve in rain water to form H₂SO₄ and HNO₃. pH of acid rain is less than 4 (Normal rain pH 5.6-6).

Effects:

• Aquatic Life: Leaches heavy metals (Al, Hg, Pb) causing suffocation in fish (clogs gills).
• Buildings: Erodes limestone (CaCO₃) and marble (Taj Mahal).
• Soil/Plants: Increases soil acidity, damages leaves, retards growth.

Ozone Layer: O₃ layer in Stratosphere (25-30 km). Protects from harmful UV radiations.

Depletion Cause: Chlorofluorocarbons (CFCs) used in refrigerants/ACs. UV breaks CFCs releasing Chlorine free radicals (Cl^*) which destroy O₃. One Cl^* can destroy 100,000 O₃ molecules.

Ozone Hole: Region of depleted ozone layer (first noticed over Antarctica).

Effects: Skin cancer, eye cataracts, infectious diseases, damage to plants/crops (disrupts food chain).