With the removal from the earth's surface air density decreases. This is because the pressure in the upper layers of the atmosphere is lower than that of the earth.
What is the relationship between air pressure and its density?
It is clear and intuitive: the lower layers of air are under the most intense pressure than the top.
What does low blood pressure and reduced air density? This means that such thin air contains fewer molecules, including molecules of oxygen. That is why at high altitude hard to breathe.
By the way...
At 0°C the mass of one cubic meter (1 m3) of air is:
- at the earth's surface - 1, 293 kilograms;
- at the altitude of 12 km - 319 grams;
- at a height of 40 km - 4 grams.