Due to altitude the higher you go the less dense air becomes. Since mountains are up so high the air is less dense than it is at sea-level. Air's density is highest at low elevations but decreases as elevation increases.
There is lower air pressure on top of mountains compared to sea level, due to the decrease in atmospheric density as altitude increases.
warm air is low densitycool air is high density
As temperature increases, density decreases.
= What is low air density? = well, high or low are relative concepts. Normally the standard air density of the air is defined as the density of the air at 15ºC and at sea level pressure (standard conditions), what give a value of 1,225kg/m3. This way, we can talk about high or low air density related to the standard value. Air density depends on temperature and pressure. The colder the temperature the higher the density is, and the higher the height in the atmosphere the lower the density becomes. In the Everest peak, e.g., air density can be lower than 0,5. Meanwhile in the Antarctica (at sea level) the density could reach values higher than 1,5.
density
Carbon dioxide has a higher density than air. This is why it can accumulate in low-lying areas and pose a risk of asphyxiation if not properly ventilated.
As temperature increases, air density decreases because the air molecules have more energy and spread out, causing the air to become less dense. Conversely, as temperature decreases, air density increases because the air molecules have less energy and come closer together, making the air more dense.
When a high density air mass pushes into a low density air mass, the denser air will typically force the less dense air to rise. This can lead to the formation of weather fronts, including cold fronts and occluded fronts, which can result in changes in temperature, precipitation, and wind patterns.
Hot air has low density because its molecules are more spread out and have higher kinetic energy, causing them to move further apart. This leads to a decrease in the air's mass per unit volume, resulting in lower density compared to cold air.
density
Air pressure decreases from high to low as one moves upwards in the atmosphere due to a decrease in air density. Conversely, air pressure increases from low to high as one moves closer to the Earth's surface where more air molecules are compressed together, creating higher pressure.
When air pressure drops temperature also drops. Thus on high mountains low air pressure is accompanied by low temperature. This is true for high atmosphere also.