What does rain smell like?

Rain itself has no scent. But moments before a rain event or as it begins, an earthy smell known as petrichor permeates the air. This comes from the moistening of the ground. Tiny microorganisms decompose dead or decaying organic matter, and a byproduct is a type of alcohol that has a strong scent. Its complex structure makes it noticeable even at extremely low levels of just a few parts per trillion air molecules.