You know that lovely smell that only appears when it rains? It's got a name - petrichor - and the science behind it is awesome. Joe Hansen from It's Okay To Be Smart explains.
Our noses can detect up to a trillion different scents, and many of them are tied very deeply to our memories and emotions. Some scents are very personal to you, such as the smell of your grandma's house, or the teddy bear you carried around everywhere as a child, and some scents are more universal. Take the scent of rain, for example. You'd be hard-pressed to find someone who doesn't identify with it on some emotional level.
That earthy odour that you can smell before and during a storm can be traced to three chemical sources, says Joe Hansen in this episode of It's Okay To Be Smart. The first one comes from ozone, which actually gets its name from the Greek word meaning "to smell". As storm clouds approach, the electrical charge of lightning splits the surrounding oxygen molecules into separate atoms, and some of those will reform into ozone. This is swept downwards by the winds that precede the storm to the vicinity of your nostrils.
Once the rain starts to fall and hit the soil below us, you'll smell something different - a new "pleasantly pungent perfume we call petrichor," says Hansen. The meaning of the word can also be traced back to Greek origins, as a combination of ichor, which means the "ethereal essence" that was believed to flowed through the veins of their gods (so, basically, god's blood) and petros, which means "the stones that form the Earth". The actual science behind the smell comes from the moment when decomposed organic material is blown airborne from dry soil, some of it lands on rocks, and is here joined by a multitude of different minerals. Falling raindrops release this mixture and send it into the air for you to smell them.
Find out more about the wonderful science of petrichor by watching this very cool episode of It's Okay To Be Smart above.
Source: It's Okay To Be Smart