In the air we breathe these are some of the important the gases:
Nitrogen: 78% (78 parts out of a hundred)
Oxygen: 20% (21 parts out of a hundred)
Carbon Dioxide: 0.03% (3 parts out of ten thousand)
Rare Gases also known as the Noble Gases, (Helium, Argon, Krypton,
Neon, Xenon and Radon together make up 0.97%)
Water Vapour (the amount varies)
Nitrogen is important in that it dilutes the oxygen, so you get
the right amount. Too much oxygen is almost as dangerous as too
little. We use the oxygen to help turn the food we eat into energy,
so we can do all the things we do. Without it we would die. Carbon
dioxide is important in that it is used by plants in a process
called photosynthesis to make food in the form of sugar and starch.
So this gas, even though there isn't much of it is essential
for life on earth. The amount of water vapour in the air changes
from day to day. The air is drier on some days than on others.
Without the water vapour in the air, our skin would dry up. Argon
is used in filling electron light bulbs and in gas layers and
arc welding. Neon is used in lights in advertising displays.
Krypton is used in bulbs, sometimes for lighting airfields as
it shines through fog better than ordinary light. Xenon is used
in lighting in high speed photographic tubes. The most common
use of helium is for filling balloons. A form of radon can be
used in treatment of tumours. We also find ozone in the air.
We get this as a discharge from cars and from an electric spark
being passed through oxygen. We also have carbon monoxide from
car exhausts. We get sulphur dioxide from anything that generates
heat or power from oil or coal containing sulphur.