Why are air spaces located near the lower surface of the leaf?

The air spaces occur in Spongy mesophyll tissue. There are large spaces in a leaf because it is for storing water and carbon dioxide which will be used for photosynthesis. The large air spaces are usually found in the spongy layer of the mesophyll. The arrangement of this spongy mesophyll facilitates the movement of gases through the mesophyll. Directly beneath each stomate at the leaf surface there is usually a small air space, called a stomatal chamber, where no mesophyll cells are present. This also aids in gas exchange.