How does atmospheric pressure change with altitude?

Atmospheric pressure decreases as altitude increases because there is less air above exerting pressure.

Atmospheric pressure is the force exerted by the weight of air in the Earth's atmosphere. At sea level, the atmospheric pressure is at its highest because there is a large column of air above pushing down. As you move higher in altitude, such as climbing a mountain or flying in an aeroplane, the amount of air above you decreases. This means there is less weight of air pressing down, resulting in lower atmospheric pressure.

The relationship between altitude and atmospheric pressure is not linear; it changes more rapidly at lower altitudes and more gradually at higher altitudes. For example, the pressure drops quickly as you ascend from sea level to a few thousand metres, but the rate of decrease slows down as you go even higher. This is because the density of air also decreases with altitude, meaning there are fewer air molecules in a given volume to exert pressure.

To give you a sense of scale, at sea level, the atmospheric pressure is about 1013 millibars (mb). At 5,500 metres, which is roughly the height of Mount Everest's base camp, the pressure drops to about 500 mb, roughly half of sea level pressure. At the summit of Mount Everest, around 8,848 metres, the pressure is about 300 mb, less than a third of sea level pressure.

Understanding how atmospheric pressure changes with altitude is crucial for various applications, such as weather forecasting, aviation, and even human physiology. For instance, pilots need to adjust cabin pressure in aeroplanes to ensure passengers remain comfortable and safe, as low atmospheric pressure can lead to altitude sickness due to reduced oxygen levels.