OCR TwentyFirst Century Science C1

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  • Created by: Nia
  • Created on: 26-08-13 16:06

Air Quality

The Atmosphere

The Earth is surrounded by a thin layer of gases called the atmosphere. The atmosphere contains:

  • About 78% nitrogen
  • 21% oxygen
  • 1% argon and other noble gases
  • Small amounts of Water Vapour, Carbon Dioxide and Other Gases.

Evolution of the Atmosphere

Scientists believe that the atmosphere probably evolved in the following way:

1. The early atmosphere was created by volcanic activity and consisted mainly of Carbon Dioxide and Water Vapour.

2. As the earth cooled, the water vapour condensed to form the oceans.

3. Simple photosynthetic organisms evolved in the oceans, adding oxygen to the atmosphere and removing the carbon dioxide.

4. Some carbon dioxide was removed due to it dissolving in the oceans and forming sedimentary rocks and fossil fuels.

Pollutants in the air

Pollutants are chemicals. They can harm the environment and our health. Human actions, such as burning Fossil Fuels, release pollutants into the atmosphere. Power stations and cars release pollutants in this way.

Pollutants can harm us indirectly. For example, Acid Rain makes rivers too acidic for organisms to survive. This affects some food chains and natural resources, e.g. trees

Pollutant- Harmful to- Why?

Carbon Dioxide- Harmful to the environment- it traps heat in the Earth's Atmosphere.

Nitrogen oxides- Harmful to the environment and Humans- it causes acid rain and can cause breathing problems and can make asthma worse.

Sulfur Dioxide- Harmful to the environment- it causes acid rain.

Particulates (small particles of solids, e.g. carbon)- harmful to the environment and humans- it makes buildings dirty, and can make asthma and lung infections worse if inhaled. 

Carbon Monoxide- Harmful to Humans- it prevents the blood from carrying oxygen, which can be fatal.

Measuring pollutants

It's possible to measure concentrations of pollutants in the air in pbb (parts per billion) or ppm (parts per million). For example, a sulfur dioxide concentration of 16ppb means that in every one billion (1 000 000 000) molecules of air, 16 molecules will be sulfur dioxide.

When measuring the concentrations of pollutants, it's important to repeat the measurements. For example, the concentration of nitrogen oxides from cars may change depending on the time of the day, the amount of traffic and the weather. Repeat measurements will allow a chemist to calculate a mean, which will give a good estimate of the true value of the concentration of the pollutant.


Elements are the 'building blocks' of all materials. There are over 100 elements. Each one is made of tiny particles called atoms. All atoms of a particular element are the same and unique to that element. Atoms can join together to from bigger building blocks called molecules.

Compounds form when the atoms of two or more different elements chemically combine. The properties of compounds are very different from the properties of the elements they're made from.

Chemical symbols and numbers are used to write formulae. A formula shows the...

  • different elements that make up a compound
  • number of atoms of each element in one molecule.

Chemical change


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