Chemistry · Both
Atmosphere & Climate
Composition of the atmosphere, greenhouse effect, human impact and common air pollutants.
Earth’s atmosphere is mainly nitrogen and oxygen. Human activity has increased greenhouse gases and other pollutants, affecting climate and air quality.
Composition of the atmosphere
Current dry air (approx):
• Nitrogen ~78%
• Oxygen ~21%
• Argon ~0.9%
• Carbon dioxide ~0.04%
Early atmosphere was different (more CO₂); oxygen increased due to photosynthesis over geological time.
Greenhouse effect and climate change
Greenhouse gases (CO₂, methane, water vapour) trap heat in the atmosphere – natural greenhouse effect keeps Earth warm enough for life.
**Enhanced greenhouse effect** from human activities (burning fossil fuels, deforestation, agriculture) → global warming and climate change.
Consequences: rising sea levels, extreme weather, changing ecosystems.
Air pollutants
• **Carbon monoxide** – incomplete combustion; toxic
• **Sulfur dioxide** – from sulfur in fuels; causes acid rain
• **Nitrogen oxides** – from engines; acid rain and respiratory problems
• **Particulates** – soot; respiratory issues
• **Carbon dioxide** – greenhouse gas
Practice questions
Try these without looking at the answers first.
Q1.What is the most abundant gas in the atmosphere?
Show answer
Nitrogen
Q2.Name two greenhouse gases.
Show answer
CO₂ and methane (or water vapour)
Q3.What causes acid rain?
Show answer
Sulfur dioxide / nitrogen oxides