After a rainstorm, you’ve likely noticed a distinct scent in the air, a familiar fragrance that often lies somewhere between damp soil and freshly watered plants. But did you know that this specific smell, a pleasant aroma experienced worldwide, actually has a name?
The Name: Petrichor
That earthy, fresh scent is called petrichor. The term was first proposed by two Australian researchers in the 1960s to describe the agreeable smell of rain. Breaking down the word, the prefix “petr” refers to stone, and “ichor” refers to an essence from the source material.
Researchers Isabel Joy Bear and Richard Thomas discovered the specific conditions under which petrichor is strongest. They found that the dry source material needs to be exposed to warm air for a long period of time before becoming wet. Furthermore, materials rich in silica or iron oxide exhibited the strongest petrichor smell.
Scented History and Science
The appreciation for this scent isn't new. In India, the rain's perfume is known as “mitti ka attar” and has been captured and sold as a perfume for several centuries. To create this unique fragrance, workers use a traditional method of steam-distilling baked clay disks that have been previously exposed to the intense sun during hot summer months. The distillers then absorb the clay essence of the vapor with sandalwood oil, which forms the base of all "attars," or scented oils.
Petrichor isn't the only pleasant fragrance brought out by rain. Researchers note that some plants secrete oils during dry periods, which are then released into the air during a rain event, adding to the refreshing bouquet.
The Smell Before the StormAnother major contributor to the scent of rain, and one often noticeable before the rain actually hits, is ozone. Ozone has a scent reminiscent of chlorine.
During a storm, lightning plays a role in its formation: it can split oxygen and nitrogen molecules in the atmosphere. When these molecules recombine and interact with other chemicals, ozone is formed. This explains why some people say they can "smell" a storm coming, they are likely detecting the presence of ozone carried on the pre-storm winds.
