Rain, What Is That Smell

Petrichor (/ˈpɛtrɪkɔːr/) is the earthy scent produced when rain falls on dry soil. The word is constructed from Greek petra (πέτρα), meaning “stone”, and īchōr (ἰχώρ), the fluid that flows in the veins of the gods in Greek mythology.

Some plants secrete oils during dry periods, and when it rains, these oils are released into the air. The second reaction that creates petrichor occurs when chemicals produced by soil-dwelling bacteria known as actinomycetes are released. These aromatic compounds combine to create the pleasant petrichor scent when rain hits the ground.

Another scent associated with rain is ozone. During a thunderstorm, lightning can split oxygen and nitrogen molecules in the atmosphere, and they in turn can recombine into nitric oxide. This substance interacts with other chemicals in the atmosphere to form ozone, which has a sharp smell faintly reminiscent of chlorine.

You can read more here – https://www.livescience.com/37648-good-smells-rain-petrichor.html