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The Atmosphere

Climate change, acid rain & ozone depletion

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Atmosphere Structure

Layers from Earth's surface up:

Troposphere: Where we live. Temperature decreases with altitude. Weather happens here.

Stratosphere: Contains ozone layer. Temperature increases (ozone absorbs UV). Aircraft fly here.

Mesosphere: Coldest layer. Meteors burn here.

Thermosphere: Outermost. Temperature increases with altitude. Aurora occurs here.

Ozone layer in stratosphere = protects us from UV radiation.

Atmosphere Composition

Clean dry air:

78% Nitrogen (N₂): Inert, mostly unusable

21% Oxygen (O₂): Breathable, supports combustion

1% Other: Argon, carbon dioxide, water vapour, neon, helium

CO₂ makes up ~0.04% but is the main climate concern.

Water vapour = variable, depends on humidity & location.

The Natural Greenhouse Effect

How Earth stays warm (GOOD):

1. Sun's rays enter atmosphere

2. Some radiation reflected back to space

3. Most absorbed by land & ocean (heating Earth)

4. Earth re-emits heat as infrared radiation

5. Greenhouse gases (CO₂, CH₄, H₂O) trap heat, re-radiate back to surface

Without this, Earth would be -18°C and lifeless. WITH it = 15°C and habitable.

Greenhouse Gases

CO₂ (Carbon Dioxide): ~410 ppm. Fossil fuel burning, deforestation. Stays in atmosphere 100+ years.

CH₄ (Methane): 25x more potent than CO₂. Cattle digestion, rice paddies, wetlands, landfills.

H₂O (Water Vapour): Most abundant GHG, but naturally controlled by hydrological cycle.

Since 1800, CO₂ increased 50% (280→420 ppm). Methane tripled.

Enhanced Greenhouse Effect

PROBLEM: Human activities increase greenhouse gas concentrations

Causes:
• Combustion of fossil fuels (coal, oil, gas)
• Agriculture (cattle methane, rice paddies)
• Deforestation (removes CO₂-absorbing trees)
• Cement production (heats limestone)
• Population growth & energy use

Result: Extra greenhouse gases trap MORE heat = global warming

Impacts of Climate Change (12 listed)

Physical impacts:

1. Higher surface & ocean temperatures
2. Melting ice sheets, glaciers, permafrost → sea level rise
3. Ocean acidification (CO₂ → carbonic acid)

Ecological impacts:

4. Disrupted food chains
5. Changed biodiversity
6. Habitat loss

Human impacts:

7. Forced migration
8. Extreme weather (floods, droughts, hurricanes)
9. Changed crop yields
10. Pest outbreaks & invasive species
11. Food shortages
12. Increased disease risk

Reducing Carbon Footprint (12 strategies)

Energy & transport:

• Reduce fossil fuel use (switch to renewables)
• Improve energy efficiency
• Transport policies (public transit, EVs)

Food & land:

• Plant-based diet, buy local & seasonal
• Reduce livestock farming
• Reforestation & afforestation

Carbon removal & policy:

• Carbon sequestration (capture CO₂)
• International agreements (Paris Agreement)
• Carbon taxation
• AI to predict impacts & model solutions

Climate Change Adaptation

Definition: Alter behaviour, practices & infrastructure to cope WITH climate change (we can't stop it now)

Agricultural: Develop drought/flood-resistant crops

Infrastructure: Better flood defences, seawalls, elevated buildings

Planning: Land use zoning (no building on floodplains/coasts)

Building design: Heat-resistant materials, better insulation

Adaptation critical for vulnerable countries (low-lying islands, Sahel, Bangladesh).

Acid Rain Formation

Three main pollutants:

Sulfur dioxide (SO₂): From burning coal/oil with sulfur. Also volcanic gases.

Oxides of nitrogen (NOₓ): From vehicle engines (heat fixes atmospheric N₂)

In the atmosphere:

SO₂ + H₂O → sulfuric acid
NOₓ + H₂O → nitric acid

These fall as rain with pH < 5.6 = acid rain

Impacts of Acid Rain

Water: Acidifies lakes/rivers → fish deaths, disrupted food webs

Soil: Becomes too acidic → nutrient leaching, crop damage

Vegetation: Leaf damage (defoliation), growth reduction, tree death

Buildings: Dissolves limestone, corrodes metals (statues, roofs)

Impacts spread across borders (Scandinavia affected by British pollution).

Managing Acid Rain

Flue-gas desulfurisation (FGD): In coal power plants, spray calcium carbonate/oxide to remove SO₂ before it escapes

Catalytic converters: In car exhausts, convert NOₓ to harmless N₂ & O₂

Transport policies: Reduce vehicle use, cleaner fuels, public transit

FGD & catalytic converters very effective (90%+ removal).

But need to be fitted to ALL sources (developing countries lag).

Ozone Depletion

Ozone layer (stratosphere) protects us from UV radiation.

Problem: CFCs (chlorofluorocarbons)
Used in aerosols & refrigerants. Released into air → stratosphere → UV light breaks CFC → chlorine atoms → destroys ozone

One chlorine atom destroys 100,000 ozone molecules.

Impacts: Higher UV reaching Earth → skin cancer, cataracts, plant damage, reduced crop yields

Ozone Protection

Montreal Protocol (1987): International agreement to phase out CFCs

Strategies:

• Ban CFCs in new products
• Alternatives (HFCs, HCFOs - safer)
• Safe disposal of old refrigerators/aerosols
• International cooperation & monitoring

Montreal Protocol = most successful environmental treaty.

Ozone hole still exists but not widening anymore. Expected recovery by 2070.

Benefits & Limitations of Management

Climate change mitigation:

Benefits: Prevent catastrophic warming, preserve ecosystems, health benefits (cleaner air)

Limitations: Expensive, requires global cooperation, fossil fuels entrenched in economy

Acid rain control:

Benefits: Fish return, forests recover, buildings saved

Limitations: Technology cost, some countries don't enforce standards

Summary: Atmospheric Health

Protecting the atmosphere:

✓ Switch to renewable energy
✓ Reduce fossil fuel combustion
✓ Plant forests (CO₂ sinks)
✓ Improve energy efficiency
✓ FGD in power plants (SO₂)
✓ Catalytic converters (NOₓ)
✓ Phase out CFCs (ozone)
✓ International cooperation (Paris, Montreal)
✓ Adapt infrastructure to climate change

Current trajectory: +3°C warming by 2100.
Paris goal: Limit to +1.5°C. Action needed NOW.