What happens when you go up in the atmosphere

Rise in altitude is directly proportional to decrease in pressure

The earth's atmosphere has its own pressure known as atmospheric pressure. The pressure level is highest right at the surface of the earth because the air at this level is supporting the weight of all the air above it. More weight above means a greater downward gravitational force. As we move up through levels of the atmosphere, the air has less air mass above it and gravity isn't strong enough to pull down a greater number of particles. So the balancing pressure decreases. This is why atmospheric pressure drops as we rise in altitude.