KEZAKO: Quelle est la composition de l’air?
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KEZAKO: Quelle est la composition de l’air?

October 17, 2019


The air around us is a gas, or, more precisely, a mix of several gas. There are 4, in large quantities: oxygen, nitrogen, argon and water steam. The percentage of water steam varies,
according to the moment and place, ecause it depends on various parameters,
including temperature. For example, in cold air, at 0°C, the water steam volume in the air
is located between 0 and 0,6%. On the contrary,
if the temperature is 30°C, this volume can go above 4%. The proportion between
the three other gas is constant if you don’t take into account water steam, that is, in dry air: about 78% nitrogen, 21% oxygen, and a little less than 1% argon. These proportions are, not only identical
from one place to another on Earth, no matter the weather, but also up to an altitude of 100km! Proportions remain the same, but the overall concentration of air
decreases with altitude. It is twice as low at an altitude of 5.5km three times as low at the top
of mount Everest (8848 m high), and ten times as low at 16 km. At 100km above sea-level, it is two million times as low: this amounts to saying
that there is almost no more air, at least, not enough to carry a plane. The World Air Sports Federation actually sets the limit between
the atmosphere and space at 100 km. Numerous gas are present in the air, even in tiny amounts,
and they can play an important part. It is the case, for example,
with carbon dioxide, CO2, whose proportion is almost 25 times
lower than argon’s, and 500 times lower than oxygen’s. Despite that, the amount of CO2 in the air
has a major impact on climate, because it is a powerful
greenhouse effect gas. Unlike the main gas, the proportion of these other gas
can vary with altitude. It is the case with ozone, for instance. There is 3 million times less ozone
than oxygen in the air around us. Yet, between an altitude of 20 and 40 km, this concentration is multiplied by 100. We call this area the “ozone layer”, even though the percentage of ozone
present in the air remains negligible. But it is enough to stop the UV-C rays,
which are highly harmful to living beings and, as a consequence, plays a major
part in the existence of life on Earth. In the air, you will not only find gas,
but also airborne particles, which are called “aerosols”. Their concentration is very fluctuating,
and may depend on local conditions: pollens, sand during sandstorms, or even ash from a volcanic eruption. There are also aerosols produced
by human activity. It is the case of, for example,
particles emitted by diesel engines, or of CFC’s – molecules made of carbon,
chlorine and fluorine. They are actually the cause of the
partial destruction of the ozone layer, which we commonly call the “ozone hole”. Ozone, which is actually trioxygen, that is a molecule made
of three atoms of oxygen, which interacts with CFC’s
and turns into dioxygen, which is the usual oxygen gas,
which does not stop UV-C rays.

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  1. Merci pour la composition exacte.
    Si ont rajoute des particules de baryum, d’aluminium j'en oublie pleins mais rien que CA vaut le zyclonB a petit doses ou les pesticides stock de 1914 sur les poilus.
    Des particules radio actives pour nous changer l'ADN et forcé aux cancer ou l'avortement pour anomalies génétiques.

  2. Je suis ici pour un cours de SPC et je trouve cette vidéo assez bien pour comprendre par rapport à mes cours !Super !

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