Atmospheric pressure decreases as altitude increases. High altitudes contain less air molecules, resulting in lower air density, decreased temperatures and lower air pressure. High altitudes are typically found above sea level.
Atmospheric pressure is measured as the weight of the air above a surface. Atmospheric pressure is affected by gravity, which is strong at lower altitudes and weak at higher altitudes. Gravity at lower altitudes causes air molecules to be pulled together, increasing the atmospheric pressure as the air becomes more dense. Atmospheric pressure experiences a rapid decrease at 5.5 kilometers above sea level and continues its decrease at a slower rate as altitude increases.