What happens in general to the air pressure as altitude increases? and why ?

pressure decreases with increasing altitude. The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any elevation. At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels.

i would have a lunch. it's one big package of food, making it one food. : p

answer; i believe the answer is hydraulic action;