When the expected summer storms blew in this past June, they brought with them certain, familiar smells. Many people simply describe the scent as “the smell of rain.” However, this odor is actually the smell of ozone, petrichor, and geosmin–the most common scents emitted before, during, and after a storm.
The scent of the ozone is often the first that one can detect, and it arrives even before a storm occurs. This odor is produced when nitric oxide reacts with other atmospheric chemicals, which can then create a molecule consisting of three oxygen atoms, otherwise known as ozone. In fact, the word ozone comes from the Greek word ozein, meaning to smell. Brought down to Earth by the downdrafts of thunderstorms, ozone's odor signifies that a storm is coming.
Petrichor, another scent commonly noticed in the summer, is especially prominent when the rain begins to fall. First defined in 1964 by mineralogists Isabel Joy Bear and R.G. Thomas, petrichor comes from molecules on the surface of decomposing plant and animal matter attached to and combined with pieces of mineral or clay. Falling rain then disturbs this combination, releasing odor into the air.
The third scent typically associated with the summer, simply described as the smell of damp earth, is geosmin. A metabolic byproduct of bacteria or blue green algae, geosmin can be smelled following rainfall.
Although the various smells associated with storms may not seem significant, they actually serve as signals for some animals. For example, microbiologist Keith Chater at the John Innes Center in England suggests that geosmin's odor might lead camels to desert oases. Other biologists suggest that the scent of petrichor in waterways can signal fish to begin reproducing.
So the next time you see dark clouds on the horizon, instead of running inside and checking the weather channel to see if it is going to rain, try using your nose instead!
[Source: Scientific American]