Air pressure is caused by the weight and motion of air molecules pressing on everything around them.

Core idea: What causes air pressure?

  • Air is made of tiny molecules (like nitrogen and oxygen) that have mass and are pulled toward Earth by gravity.
  • This whole ā€œocean of airā€ stacked above you has weight, and that weight pushes down on the surface, creating atmospheric pressure.
  • On a microscopic level, air pressure is also the result of air molecules constantly moving and colliding with surfaces (and with each other); more or faster collisions mean higher pressure.

Think of standing at the bottom of a swimming pool: the water above you has weight, so it presses on you. The atmosphere works the same way, just with invisible gas instead of water.

Main factors that create and change air pressure

1. Gravity and the ā€œair columnā€

  • Gravity pulls air molecules toward Earth, so the air near the ground is more compressed and denser; this makes pressure higher at sea level than on a mountain.
  • A spot on Earth with more total air mass stacked above it will have higher surface pressure; less mass above means lower pressure.

2. Air density (how tightly packed the air is)

Air density changes air pressure in two big ways:

  • If you pack more molecules into the same space (higher density), there are more collisions with surfaces, so pressure rises.
  • If there are fewer molecules in that space (lower density), there are fewer collisions, so pressure drops.

In the atmosphere, colder air is denser and tends to give higher pressure at the surface, while warmer air is less dense and often linked to lower pressure areas.

3. Temperature

Temperature controls how energetic the molecules are:

  • Warmer air: molecules move faster, spread out more, and rise; as air rises and spreads aloft, the surface below often ends up with lower pressure.
  • Colder air: molecules slow down and pack more tightly, often sinking and increasing surface pressure beneath them.

This temperatureā€“pressure relationship is why weather maps show shifting high- pressure (often clearer) and low-pressure (often stormier) systems.

4. Motion of air (winds and circulation)

  • Large-scale wind patterns and circulation can ā€œpile upā€ air in one region, increasing the mass of air above that area and raising pressure.
  • Where air is diverging or flowing away aloft, the mass of air above decreases, leading to lower pressure at the surface.

Mechanical processes (like air being blocked by mountains or converging into a storm) can therefore raise or lower pressure, even without big temperature changes.

Why pressure changes from place to place

Putting it together, different locations get different air pressures because of combinations of:

  1. Gravity and altitude (how much air is above you).
  2. Temperature differences (warm vs cold air masses).
  3. Air density (how compressed the air is).
  4. Large-scale weather patterns and winds that move air around.

For example, a cold, dense air mass sitting over a region with air slowly sinking tends to form a high-pressure system with clearer weather, while a warm, rising air mass where air is spreading out aloft tends to be a low- pressure system associated with clouds and rain.

TL;DR:
Air pressure exists because air has weight and is pulled down by gravity, and because moving molecules constantly hit surfaces; changes in temperature, density, altitude, and air movement make pressure go up or down.

Information gathered from public forums or data available on the internet and portrayed here.