Standard atmospheric pressure in atm

Both temperature and altitude affect barometric pressure. Air pressure varies with altitude; it is always lower at high altitudes, regardless of weather. Cool air is less dense than warm air because there are fewer collisions between air molecules.

This results in lower air pressure. For example, 500 mb of air pressure occurs at a lower altitude for cooler air.

What is atmospheric pressure at sea level

Warm air expands, so 500 mb of air pressure is found at higher altitudes. 500 mb of air pressure in Canada would likely occur at a lower altitude than in Mexico.

To compare air pressure at different elevations, weather observers must correct for the effect of altitude by adding the air pressure that would be exerted at sea level.

For example, if air pressure measures 840 mb at an elevation of 1,000 meters above sea level, the measurement adjusted for sea level is 1,020 mb. Without correcting for air pressure at sea level, the air pressure on the top of Mt.

Everest is near 300 mb.