https://en.wikipedia.org/wiki/Petrichor

this is great to know actually

When a raindrop lands on a porous surface, air from the pores forms small bubbles, which float to the surface and release aerosols. Such aerosols carry the scent, as well as bacteria and viruses from the soil.

The human nose is sensitive to geosmin and is able to detect it at concentrations as low as 0.4 parts per billion. Some scientists believe that humans appreciate the rain scent because ancestors may have relied on rainy weather for survival.