What factors affect air pressure?

Answer 1

Fundamentally air pressure iscontrolled at the earths surface by the mass/weight of the column of air above a piece of ground.
Assuming the atmosphere is of constant thickness (i.e. the height of the column of air remains constant), then the weight of the air will be controlled by the temperature of the air in the column. This is because warm air take up more volume than cold air thus if the column of air is cold the weight/pressure will be high while if the air is warm the pressure will be low.
Apart from over a volcano, the air on the Earth is warmed by the Sun and therefore from the equator to the poles the temperature of the air column will fall which means that the pressure should be high at the poles and low at the equator. However things are not that simple because where you have pressure differences the air masses in the columns will move to equalize them and this causes a convecting air current to begin to form. And as warm air is taken upward it cools and sinks again and so a cycle forms which gradually moves warm air form the equator towards the cold polar areas. Further, the spinning of our planet causes this circulation pattern to rotate as it moves north or south. This means that what we end up with are areas of low and high (warm and cold) air moving across the planet in a rotating motion called cyclones (low pressure areas) and anticyclones (high pressure areas).
It can affect you

Answer 2

P = F/A

Pressure = Force / Area

If you have a 2KG weight on your hand it does not hurt, but if its balancing on a pin on your hand it will most probably Hurt like nothing else. The weight did not increase, only the pressure increased as the force was divided by a smaller surface.

Answer 3

temperature and altitude =D

Answer 4

Temperature and Altitude