What is clean air made up of?

Why do these percentages change very little?

Some of these processes are shown in the carbon cycle. Draw the carbon cycle.

Over the last few centuries the percentage of carbon dioxide in air has increased slightly due to a number of factors. Name two of these factors and why they have contributed to this increase.

What formed the original atmosphere?

What did plants that could photosynthesise do?

Where do gases come from?

What do scientists do to form theories about the original atmosphere?

Describe one theory about the Earth's early atmosphere.

Why is it important to control atmospheric pollution?

Sulfur dioxide is a pollutant. What can sulfur dioxide cause?

A car is fitted with a catalytic converter. What is a catalytic converter?

What does a car fitted with a catalytic converter do?

In a catalytic converter what reaction takes places on the surface of the catalyst?

Which two gases are formed in this reaction?

Write the balanced symbol equation for the reaction between nitric oxide and carbon monoxide which takes place in a catalytic converter.

What is a catalyst?