Air pressure is greater at sea level primarily due to the weight of the atmosphere above us. The Earth’s atmosphere is made up of a mixture of gases, and as you go higher in elevation, there is less of this atmosphere pressing down on you.
At sea level, we are at the base of the atmospheric column, and all the air above us contributes to the pressure we feel. As altitude increases, there’s less air above to exert pressure, which results in lower atmospheric pressure. This is why if you’ve ever climbed a mountain or gone to a high elevation, you may have noticed the change in how difficult it can be to breathe.
In addition, temperature and weather conditions can also affect air pressure. Warm air tends to rise, causing lower pressure at the surface, while cooler air can sink and increase air pressure. However, at sea level, we generally see the highest air pressure due to the density of air and the gravitational pull that retains it closer to the Earth’s surface.