A Look at the Origins of Petrichor, the Distinctive Smell of Rain

December 10, 2024 | 11:11 am

TEMPO.CO, Jakarta - When the rain falls, the petrichor scent starts to be wafted. This gentle scent is often described as the smell of rain, earth, or nature. The petrichor scent also helps transform a person's environment.

As quoted from Green Turf, the combination of petrichor aroma and the peaceful sound of raindrops provide a strong sense of relief in the human brain. This scent can alleviate anxiety or depression and help alleviate temporary symptoms due to human innate biophilia.

So, where does the smell of rain or petrichor come from?

Petrichor was introduced by two scientists from Australia, Isabel Joy Bear and Richard Grenfell, in 1964. They defined petrichor as a unique scent that appears after rain falls on dry soil. They found that this unique scent emerges from the release of various volatile compounds by plants and microbes.

Petrichor comes from the Greek language consisting of two words, namely petra and ichor. Petra or petros means stone, while ichor means the noble blood of gods and goddesses. The petrichor scent originates from actinomycetes bacteria. During the dry season, these plants produce oil that is absorbed by the soil.

When it rains, this oil is released into the air along with other compounds. One of them is geosmin, a metabolic byproduct of actinobacteria. Geosmin contains 79.06 percent oxygen, 12.17 percent hydrogen, and 8.77 percent oxygen. When it rains, geosmin is released from the soil and mixes with ozone molecules.

Thunderstorms also play a role in creating petrichor by generating electrical discharge in the atmosphere. This produces a clean and sharp ozone scent. Professor Maribeth Stolzenburg from the University of Mississippi explains that thunderstorms, especially during rain, improve air quality. Most of the dust, aerosols, and other particulates that come into contact with rainwater make the air clean.

Furthermore, acid rain also affects the formation of the rain or petrichor scent. These acids come from the soil and plants known as Palmitic acid and Stearic acid. Sometimes, petrichor formed from these acids can make the rain scent unpleasant and undesirable to smell.

Because these acidic chemicals are found in organic debris such as bacterial spores, fuel residues, and so on. The more infrequently the rain falls in an area, the first rain will release a stronger petrichor than usual.

On the other hand, the rain scent may also be influenced by the flora in an area. Some plants release oil during dry periods. When it rains, the oil scent is released into the air. Stearic and palmitic acid can add to the rain scent.

Another scent related to rain is ozone. When lightning breaks down oxygen and nitrogen molecules in the atmosphere, then recombines into nitric oxide. This substance interacts with other chemicals in the atmosphere to form ozone. When someone can smell the rain scent, the wind may have carried ozone until it is inhaled into the nose.

Idris Boufakar and Naomy Ayu Nugraheni contributed to this article.

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