This Science Explains Why You Can Smell Rain

Some people swear they can smell the weather. Lorelei Gilmore from the Gilmore Girls even made it part of her personality –  she could smell snow before it happened. But did you know that you really can smell the rain? Well, not precisely rain, but the ground after it rains. And it's not exactly because rainwater is dirty.

This is called petrichor, the smell of the first drops of rain as they hit the ground after a long dry spell. Petrichor is more than a perfume featured on an Eleventh Doctor episode of Doctor Who, it's an actual scientific word coined in 1964.

Petrichor is a combination of different fragrances and chemical reactions of microorganisms, according to Discover Magazine. Chief among them are actinobacteria, a microorganism that decomposes dead or decaying organic matter. These release something called geosmin which is like a type of alcohol and has a strong enough smell for people to perceive. During drier periods, actinobacteria slow down. But when rain is imminent, the air becomes moist and the actinobacteria start coming alive and produce more geosmin.

Once rain hits the ground, the microorganisms splatter into the air. Aerosols are released and carried to surrounding areas. Scientific American reports that petrichor smells different depending on where rain falls. More rural areas with lots of trees and vegetation release a different smell than a city, where actinobacteria live on concrete.

Only happy when it rains

Petrichor is the smell that rain releases but it isn't the only reason why people can tell if rain is imminent. Per Scientific American, the ozone layer also gives off a fragrance.

Ozone has a sharp, sweet smell which also emanates from fertilizers, pollutants, and other natural sources. When an electrical charge hits the air either from lightning or maybe even a generator, it splits nitrogen and oxygen atoms which then sometimes bond three oxygen atoms to form ozone. Downdrafts of wind from a thunderstorm carries these ozone molecules to our noses. If it kind of smells like chlorine in a swimming pool, says Smithsonian Magazine, it's because you smell ozone and it's probably going to rain soon.

Many people associate the smell of rain, whether it's petrichor, ozone, or both, with pleasant relaxing feelings. The Smithsonian Magazine writes it's because people over the years have equated rain with greenery and the feeling of renewal. After all, rain brings much-needed water to dried out fields. So if a friend tells you they can smell rain coming, bring an umbrella, because they're picking up on a scent straight from the heavens.