The Air "is Thin" as Pressure Drops

What Are You Breathing?
If you have just come from the page Air Pressure and Atmospheric Density this page will make more sense to you. You may want to go there for a quick review.

     We hear people say that "the air gets thin" as we climb up mountains. We hear information about oxygen masks when we ride in planes, and mountain climbers take oxygen with them as they climb high peaks.

     What does all this really mean?

     Let's think about the air that we are breathing. How much air do we take in at a breath? An average woman takes in 4.5 liters. Athletes may take in 6 liters or more. (The cyclist Miguel "Big Mig" Indurain has a lung capacity of 7.8 meters!) Let's go with 5 liters per breath to make the math simple.



One atmosphere = 14.7 pounds of pressure per square At sea level, air pressure on earth is called one atmosphere.inch.

When you take a 5 liter breath at one atmosphere you are taking in

760 mm of mercury = 1 atmosphere of pressure

A scientist called Robert Boyle (1627-91)worked with gases. He came up with Boyle's Law which says that

Pressure multiplied by volume = mass multiplied by (a constant) multiplied by temperature





n=the mass, i.e., the number of moles

a mole = the number of molecules is 6.023*10^23

1 mole = 24 liters of atmospheric gas at sea level at 25 degrees celsius


50 billion molecules; volume of 8 liters at 5 atmospheres of pressure

10 billion molecules; volume of 8 liters at 1 atmospheres of pressure

Header from NASA Earth From Space