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O Level · Chemistry 0620

Air Quality & Climate

Revise Air Quality & Climate for Chemistry 0620 (O Level) — revision notes and instant AI marking.

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Quick Overview

📊 Air & Pollution

  • 78% nitrogen, 21% oxygen
  • Pollutants: CO₂, CO, particulates, CH₄, NOₓ, SO₂
  • Each has different sources and effects

🌡️ Greenhouse Effect

  • Natural: keeps Earth warm
  • Enhanced: too much gas traps too much heat
  • Causes global warming and climate change

🔧 Solutions

  • Renewable energy instead of fossil fuels
  • Catalytic converters in cars
  • Reforestation and lifestyle changes

🌿 Photosynthesis

  • Plants remove CO₂ from air
  • Convert it to glucose and oxygen
  • Key part of carbon cycle

💨 Acid Rain

  • Caused by NOₓ and SO₂
  • Damages buildings and ecosystems
  • Can travel vast distances in wind

⚗️ Combustion Types

  • Complete: excess O₂ → CO₂ + H₂O
  • Incomplete: limited O₂ → CO + H₂O + soot
  • Determines pollutants produced

1. Air Composition & Air Pollution

Natural Air Composition

The air in Earth's atmosphere has stayed remarkably stable for the last 200 million years. It consists of:

  • 78% Nitrogen (N₂) — largely unreactive in the atmosphere
  • 21% Oxygen (O₂) — essential for combustion and respiration
  • 0.9% Argon and noble gases
  • 0.04% Carbon dioxide — crucial for photosynthesis

These five components make up virtually all of the air we breathe. The beauty of this composition is that it's been sustained naturally for millions of years through cycles like photosynthesis and decomposition.

What Is Air Pollution?

Air pollution occurs when gases produced by human activities are added to the atmosphere. These gases are not naturally present in harmful quantities, and they damage air quality and human health. The main culprits come from burning fossil fuels, industrial processes, and farming.

💡 Key Insight: Natural greenhouse gases like CO₂ and methane already exist in air. The problem isn't that they exist — it's that human activities are adding far too much, too fast.

Pollutant 1: Carbon Dioxide (CO₂)

Sources:

  • Complete combustion of carbon-containing fuels (coal, oil, gas, wood)
  • Power stations, vehicles, heating systems, factories

The Chemistry: When a fuel burns completely in excess oxygen, all the carbon forms CO₂:

Complete Combustion Example CH₄ + 2O₂ → CO₂ + 2H₂O
Methane (from natural gas) reacts with oxygen to produce carbon dioxide and water. This is the "cleanest" type of combustion, but it still produces CO₂.

Adverse Effects:

Pollutant 2: Carbon Monoxide (CO)

Sources:

The Chemistry:

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Also in the full note
  • 2. The Greenhouse Effect & Global Warming
  • 3. Acid Rain
  • 4. Strategies to Reduce Environmental Issues
  • 5. Catalytic Converters (Extended Tier)
  • 6. Photosynthesis & the Carbon Cycle
  • What to Memorise
  • Concepts Checklist
  • ⚠️ Exam Tips & Common Pitfalls
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