Atmospheric pressure, often called air pressure, is the fundamental force exerted by the weight of the entire column of air in the atmosphere pushing down on the Earth’s surface. This pressure is the cumulative result of air molecules being pulled toward the Earth by gravity. At sea level, this results in a measurable pressure beneath an immense mass of gas molecules.
The Directional Answer: Altitude Causes Pressure to Drop
Atmospheric pressure decreases significantly with altitude. As elevation increases, such as traveling from a low elevation like a beach to a high elevation like a mountain peak, the air pressure steadily drops. This means air molecules are less compressed, resulting in a lower force exerted on any surface. For instance, at the top of Mount Everest, the atmospheric pressure is only about one-third of the pressure felt at sea level.
Understanding the Air Column and Density
The drop in pressure is directly related to the concept of the air column—the total mass of air directly above a measurement point. At sea level, the column of air extends to the top of the atmosphere, meaning the entire mass of air is pressing down. When climbing a mountain, a person leaves a large portion of that air mass below them, effectively shortening the column of air overhead. A shorter column translates to a lower weight and thus lower pressure.
This phenomenon is compounded by the effect of gravity on air density. Gravity pulls air molecules toward the Earth’s center, causing the air to be compressed and packed tightly together near the surface. Consequently, air is densest at lower altitudes, where the weight of the air above squeezes the molecules together. As altitude increases, there are fewer air molecules above to exert compressive force, which allows the air to become progressively thinner and less dense. The pressure decreases exponentially with altitude as the air mass thins out.
Practical Impacts of Reduced Pressure
The reduction in atmospheric pressure at high altitudes has several observable effects on the human body and daily life.
One physiological consequence is difficulty breathing, as lower pressure means the partial pressure of oxygen is also lower. This lack of available oxygen leads to altitude sickness in unacclimated individuals. Commercial aircraft, which cruise at altitudes where the external pressure is extremely low, must use pressurized cabins to maintain an interior environment comparable to sea level.
A more common experience is the temporary discomfort or “popping” in the ears during rapid ascent or descent, such as in an elevator or an airplane. This sensation happens because the air pressure inside the middle ear is briefly out of balance with the rapidly changing external pressure. Changes in pressure also cause physical effects, such as water boiling at a lower temperature at high elevations. Since boiling occurs when the liquid’s vapor pressure equals the surrounding atmospheric pressure, the lower air pressure allows water to boil before it reaches the standard 212°F (100°C). This lower boiling temperature increases cooking times. Weather professionals use instruments called barometers to measure these changes, as a drop in atmospheric pressure can indicate an incoming storm system.