Question

what is the effect of altitude on atmospheric pressure

Answer 1

Altitude affects air pressure due to gravity. Gravity causes the pressure to increase or decrease based on the air's distance from sea level.

Answer 2

At sea level you have the highest pressure of the atmosphere, as you gain altitude from sea level atmospheric pressure decreases. It decreases because of gravity, gravity becomes lower as you gain altitude. Why? Because higher gravity, at sea level compresses the atmosphere the most. If you take the atmosphere’s oxygen at sea level, you have more or less 21% which is oxygen. As you gain altitude the atmosphere is compressed less, more or less you lose 10% of oxygen for every 1000 meters of altitude.