Chemistry of the atmosphere

What was Earth’s early atmosphere like?

• Mostly carbon dioxide (CO₂)

• Very little or no oxygen (O₂)

• Other gases: water vapour (H₂O), nitrogen (N₂), methane (CH₄), ammonia (NH₃)

Where did Earth’s early gases come from?

Volcanic activity released CO₂, water vapour, and other gases.

How did oceans form and affect CO₂ levels?

• Water vapour condensed → oceans formed.

• CO₂ dissolved in oceans and formed sedimentary rocks (e.g. carbonates).

How did photosynthesis change the atmosphere?

Algae and plants evolved → Photosynthesis reduced CO₂ and increased O₂.

What is the balanced equation for photosynthesis?

• 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What is the composition of Earth’s atmosphere today?

• 78% nitrogen (N₂)

• 21% oxygen (O₂)

• ~1% other gases (CO₂, water vapour, noble gases)

What caused the drop in atmospheric CO₂ over time?

• Formation of oceans (dissolved CO₂)

• Formation of sedimentary rocks and fossil fuels

• Photosynthesis

What are the main greenhouse gases?

• Carbon dioxide (CO₂)

• Methane (CH₄)

• Water vapour (H₂O)

How do greenhouse gases cause the greenhouse effect?

They absorb longwave infrared radiation from Earth and re-radiate it in all directions, warming the atmosphere.

What human activities increase greenhouse gases?

• CO₂: Burning fossil fuels, deforestation

• CH₄: Cattle farming, rice fields, landfill sites

What are the potential effects of global climate change?

• Rising sea levels

• More extreme weather

• Changes in rainfall and temperature

• Habitat loss and species extinction

• Food and water insecurity

What are carbon footprints?

Total amount of CO₂ and other greenhouse gases emitted over the full life cycle of a product or activity.

How can carbon footprints be reduced?

• Using renewable energy

• Energy efficiency

• Carbon capture and storage

• Carbon offsetting (e.g. planting trees)

• Taxing carbon emissions

What is complete combustion?

Fuel + plenty of oxygen → produces CO₂ and H₂O

What is incomplete combustion?

Fuel + limited oxygen → produces carbon monoxide (CO), soot (carbon), and water

Why is carbon monoxide dangerous?

• It is colourless, odourless, and toxic.

• Binds to haemoglobin and prevents oxygen transport in blood.

What problems does soot (particulates) cause?

• Global dimming (reduces sunlight reaching Earth)

• Respiratory problems when inhaled

How is sulfur dioxide (SO₂) formed?

From sulfur impurities in fuels during combustion.

How are nitrogen oxides (NOₓ) formed?

Formed at high temperatures in engines from nitrogen and oxygen in the air.

What are the effects of SO₂ and NOₓ?

• Cause acid rain (damages buildings, kills plants and aquatic life)

• Cause respiratory issues

Why is climate change a difficult issue to address?

• Scientific complexity

• Uncertainty in predictions

• Political, economic, and social disagreements

Why is peer review important in climate science?

• Ensures data reliability

• Avoids bias and misinformation

• Helps inform policy decisions

Why do some people remain sceptical about climate change?

• Misinformation

• Economic/political interests

• Confusion between natural climate variation and human impact

What natural processes remove CO₂ from the atmosphere?

• Photosynthesis

• Dissolving in oceans

What natural processes add CO₂ to the atmosphere?

• Respiration

• Volcanic activity

• Combustion

• Decomposition

What human activities disrupt the carbon cycle?

• Burning fossil fuels

• Deforestation