Explain briefly the factors that affect Atmospheric Pressure.

The factors that affect Atmospheric Pressure are:

1. Altitude — Atmospheric Pressure decreases with increase in altitude at rate of 1 cm of mercury for every 110 m of ascent. Atmospheric Pressure is highest at sea level.
2. Temperature — Atmospheric Pressure decreases with increase in temperature.
3. Water Vapour — Water Vapour concentration affects atmospheric pressure because molecular weight of water (18 g/mol) is less than the average molecular weight of air (about 29 g/mol). Therefore, humid air is less dense and exerts less pressure than dry air.
4. Rotation of the Earth — Due to rotation of earth, bulk of the air at the poles is thrown away towards the Equator. This creates low pressure in Equatorial regions as they are hot whereas at the poles, the cold heavy air sinks down and creates high pressure. In fact, temperature and rotation of the earth together contribute to the formation of world pressure belts.