To hear audio pronunciation of this topic, purchase a subscription or log in.

[Gr. aēr, air]
The invisible, tasteless, odorless mixture of gases surrounding the earth. Air at sea level consists of approx. 78% nitrogen and 21% oxygen by volume. The remaining constituents are water vapor, carbon dioxide, and traces of ammonia, argon, helium, neon, krypton, xenon, rare gases, and some pollutants.

There's more to see -- the rest of this topic is available only to subscribers.