7.1-7.4: The Atmosphere & Human Activities Notes:

The Atmosphere

Structure of the Atmosphere

• Troposphere (0–14 km): densest layer, contains most water vapor, weather occurs here, temp decreases with altitude.

• Stratosphere (14–50 km): dry, thin air, temp rises due to ozone layer (19–48 km) absorbing UV radiation.

• Mesosphere (50–85 km): coldest layer (~–100°C), meteors burn up, ice clouds visible at sunset.

• Thermosphere (85–600 km): temp rises to 1000°C, auroras form, ISS orbits here.

• Exosphere (600–10,000 km): merges into space, satellites orbit.

Composition

• Nitrogen (78%), Oxygen (21%), Argon (0.9%).

• Trace gases: CO₂, methane, nitrous oxide, ozone, neon, helium.

• Human activity modifies proportions → climate change.

The Ozone Layer

• Found in stratosphere (19–48 km).

• Absorbs/scatters harmful UV radiation.

• Protects plants, animals, humans from damage.

Natural Greenhouse Effect

• Greenhouse gases (water vapor, CO₂, methane, ozone) trap outgoing long‑wave radiation.

• Keeps Earth habitable (~15°C average).

• Without it, Earth would be ~–18°C.

Atmospheric Pollution and Its Causes

Smog

• Somg is a term used to describe visible air pollution.

• Causes: coal burning, VOCs (paints, petrol, cleaning products), vehicle emissions, industrial processes, forest fires, photochemical reactions, temperature inversions.

• Photochemical smog: sunlight + NOx + VOCs → ground‑level ozone.

• Temperature inversion: traps polluted air near surface.

Acid Rain

• Causes: SO₂ + NOx from power stations, vehicles, industry → sulfuric/nitric acid in rain.

• Can travel long distances via prevailing winds.

Ozone Layer Depletion

• Cause: CFCs (aerosols, refrigerators) release chlorine → destroys ozone.

• Greatest depletion in polar regions (Antarctica “ozone hole”).

• Montreal Protocol (1989) banned CFCs → recovery started.

Enhanced Greenhouse Effect

• Human activity (fossil fuels, agriculture, vehicles) increases CO₂, methane.

• More heat trapped → global warming.

• CO₂ levels rose from <300 ppm (historic) to >400 ppm today.

Impact of Atmospheric Pollution

Smog

• Human health: burning eyes/throat, coughing, asthma attacks, respiratory disease, heart attack risk.

• WHO: outdoor air pollution kills >3 million annually.

Acid Rain

• Water: acidifies lakes/streams, kills fish, reduces biodiversity.

• Vegetation: damages roots, reduces soil fertility, lowers crop yields.

• Buildings: corrodes stone, metal, paint.

Ozone Depletion

• More UV radiation → higher skin cancer, cataracts.

• Damages plant tissues, reduces growth.

• Disrupts ecosystems/food webs.

Climate Change (Enhanced Greenhouse Effect)

• Melting ice sheets, glaciers, permafrost.

• Sea‑level rise → flooding, land loss, forced migration.

• Ecosystem shifts, species extinction risk.

Managing Atmospheric Pollution

Individual Strategies

• Reduce carbon footprint: public transport, fly less, use renewable energy, recycle, eat local.

• Energy efficiency: smart meters, insulation, efficient boilers.

Government Strategies

• Transport policies: taxes on polluting cars, road pricing, investment in public transport.

• Taxation: green taxes on emissions, subsidies for clean energy.

• Reforestation/Afforestation: absorb CO₂, restore habitats.

• Flue‑gas desulfurisation: scrub SO₂ from power station emissions.

• Catalytic converters: reduce CO, NOx from cars.

International Strategies

• Paris Agreement (2016): limit warming <2°C, finance low‑carbon development.

• Montreal Protocol (1989): banned CFCs → ozone recovery.

• Carbon capture & storage: trap CO₂ from power stations, store underground.

NOTES DONE BY FARIDA SABET

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