The Earth is surrounded by a thin layer of gasses called the ATMOSPHERE. It is about 15km thick. Air forms part of the atmosphere - it is a mixture of different gases consisting of small molecules with large spaces between them.
There are also small amounts of water vapour, carbon dioxide and particulates.
When it comes to I/GCSE Chemistry, the amount of water vapour and polluting gases varies as a result of human activity or by natural processes (e.g. volcanoes). Many of these gases affect the quality of the air we breathe. Gases released in one part of the world will gradually spread through the atmosphere and can affect the air quality of people miles away.
THE EARTHS EARLY ATMOSPHERE
Since the formation of the Earth, 4.6 billion years ago, the atmosphere has changed a lot.
- The earliest atmosphere volcanoes.
- As the temperature of the planet fell, the water vapour in the air condensed to form oceans and seas.
- The evolution of photosynthesising organisms started to reduce the amount of carbon dioxide and increase the amount of oxygen in the atmosphere.
- Carbon from carbon dioxide in the air was removed from the atmosphere by dissolving in the oceans and then became locked up in sedimentary rocks as carbonates and fossil fuels.
- Clean air contains about 78% nitrogen, 21% oxygen and 1% other gasses including 0.035% carbon dioxide.
Normal air contains varying amounts of water vapour and some polluting gases.
Human activity has changed the composition of the atmosphere by adding small amounts of carbon monoxide, nitrogen oxides and sulphur dioxide to the atmosphere AND extra carbon dioxide and small particles of solids (e.g. carbon) to the atmosphere.
POLLUTANTS that harm the environment can also harm humans indirectly. For example:
Acid raid makes the water in rivers and lakes to acidic for plants and animals to survive → This has a direct impact on our food chain and natural resources like trees.
A low concentration of pollutants
– There are very few pollutant molecules in a certain volume of air. This is an indication of GOOD air quality
A high concentration of pollutants
– There is a large number of pollutant molecules in a certain volume of air. This shows that the air quality POOR
The quality of air where you live depends mostly on nearby sources of air pollutants, and the weather:
SOURCES: vehicles, power stations and industry are some of the main sources of air pollutants.
WEATHER: pollutants are mixed up and carried around by the winds. Wind can move the pollutants many miles and even carry them from one country to another.
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