How does altitude affect atmospheric pressure and composition?

Altitude affects atmospheric pressure by decreasing it, and marginally alters the composition of the atmosphere.

As altitude increases, atmospheric pressure decreases. This is because atmospheric pressure is the force exerted by the weight of air molecules above a given point. At sea level, there is a large column of air above us, exerting a high pressure. As we ascend, the column of air above us becomes smaller, hence the pressure decreases. This is why it's harder to breathe at high altitudes - there's less pressure to 'push' the air into our lungs.

The composition of the atmosphere also changes with altitude, but not as significantly as pressure. The atmosphere is primarily composed of nitrogen (78%) and oxygen (21%), with the remaining 1% consisting of argon, carbon dioxide, and trace amounts of other gases. This composition remains relatively constant up to about 80-100 kilometres above the Earth's surface. Above this, in the thermosphere and exosphere, lighter gases like hydrogen and helium become more prevalent. However, these regions are so thin that they contribute little to the overall composition of the atmosphere.

The decrease in atmospheric pressure with altitude also affects the weather. Lower pressure means air molecules are more spread out, which leads to lower temperatures. This is why mountain peaks are often snow-capped, even in tropical regions. Furthermore, the decrease in pressure can affect the boiling point of water, making it lower at high altitudes. This is why cooking instructions often vary for high-altitude locations.

In summary, altitude has a significant effect on atmospheric pressure, causing it to decrease as we ascend. The composition of the atmosphere also changes, but to a lesser extent, with lighter gases becoming more prevalent at extremely high altitudes. These changes have various implications, from breathing difficulties to alterations in weather and cooking conditions.