Question: What are you smelling if you smell petrichor?
Answer: Petrichor is the earthy, usually quite pleasant odor of rainfall after a dry spell. Bacteria, plants, and ozone all play a role in producing the smell, particularly a molecule known as geosmin produced by a certain type of bacteria after a rain shower. Humans are extremely sensitive to that smell, and geosmin is increasingly being used as an ingredient in perfumes.
