Scientists Finally Figured Out Why Rain Smells So Good

When it rains we get the strong yet pleasant aroma from the wet earth and clean air breeze. It is both appealing and satisfying; giving a sense of relaxation and has a soothing effect. This pleasant aroma not only has been investigated by the scientists but painstakingly by the experts from the perfume industry as well.

On the other hand, it has been a focal point for poems and songs too.

Researchers soon realized that there is a complicated chemistry behind this strange aroma. It grabs attention also by the facts that not only it is hard to recreate it but those who have been successful have kept their formulas well away from the public eyes.

Picture credits: Jeremy Segrott via Flickr

The aroma is known exactly as “Petrichor”.

The term “Petrichor” was essentially named by two Australian scientists, Isabel Joy Bear and Richard Thomas in their literature published in the year 1964.

The term was derived from Greek word “Petros”, meaning “stone”, and “Ichor”, meaning “the fluid that flows in the veins of the gods”; hence the term “Petrichor” was formed.

The Dazzling Chemistry Behind Petrichor

To understand this aroma better we have to see it’s causing factors or the dazzling chemistry behind it. The characteristic aroma is believed to be factored in by bacteria, plants and even lightning. The complicated chemistry of this aroma has been thoroughly investigated by the scientists, and as per them, it is a result of changes occurring when it is about to rain, and when the rain actually begins.

Mary Halton a Science Reporter of the BBB News highlights that the aroma is associated with the molecule known as Geosmin which is produced by the Streptomyces bacteria. And, further details about thunderstorms producing the smell of ozone and the link of Geosmin relation with Terpenes (scent causing source in plants).

In an article authored by Howard Poynton, the Research Group Leader (Materials Characterisation) of  Commonwealth Scientific and Industrial Research Organisation emphasized that the aroma itself comes about when there is an increased humidity level in the atmosphere just before the actual rain. As a result of this, the pores of rocks, soil, etc experience a slight presence of water in them.

This change in the pores causes expulsion of oil from them and hence “Petrichor” is released in the environment. And, when the actual shower occurs, this release of “Petrichor” is sped up.

Interestingly, scientists from the Massachusetts Institute of Technology observed the Petrichor process with the aid of super slow motion video cameras. They observed that when a rain droplet strikes a porous medium, it strangles minute air bubble at the point of engagement. And, ultimately, the trapped bubbles exploded into the air. The research further studied the volume of gas expelled.

According to Mano Miso, a researcher, there are two types of smells associated with the rain:

  1. Good rain smell which is similar to the fragrance in the woods
  2. Bad rain smell caused by the acidity of the rain

Acid rain is a usual case nowadays in the urban settlements. The article further emphasized that sometimes cloud cover keeps the pollution close to the ground surface. And, due to pollution, the rain becomes acidic which may be sensitive to allergy patients.

The Affection With The Aroma

Rain is an essential element of our great ecosystem. As far as at ancient times the rain has been of great interest to human beings; especially at that time, it was considered more than necessary for the survival of human settlements.

Psychologists believe that this close relationship of human beings with rain since early times has established a natural instinct in humans to see rain as a sign of blessing. And, so is the case with its aroma.

Picture credits: Pixabay

Entry Into The Perfume Industry

Experts from the perfume industry have been keen to learn more about the rain fragrance to achieve higher business prospects. In India, it is a century-old practice of recreating this fragrance. It is known locally by the name of “Mitti Attar”. There are abundant perfumeries in Kannauj city of India. The process followed back then involved extraction of clay from the topsoil and then baking it in a kiln. Followed by water submersion in copper cauldrons. Subsequently, the mixture was sealed with soil and cauldron was subjected to heating. The vapors caused by heating then transit through pipes and ultimately condensed. And, hence the final product “Mitti Attar” was produced.

This process in scientific terms is simply hydro-distillation.

Producing “Mitti Attar” is an income source today for many families across India and Pakistan. These families often large in size are destined to follow their family business. Although the process of making “Mitti Attar” may seem simple and straightforward but the exact technique of making it is still kept a secret since it’s discovery, and only a handful of people know it. The secret formula has been relaying over within these families; where parents pass it over to their children and the process continues. Outsiders are usually not allowed to intervene in the production process and even if they are, they are assigned simple tasks only.

A perfumer from India with an interview with the “The Asian Age” stated:

I don’t know the formula myself. Even the factory workers don’t know it. They just follow instructions

Likewise, well-known perfume brands in the modern era who have discovered the formula and devised highly complex scientific processes to recreate the aroma have adopted strict security measures to keep it a secret.

In Summary

Rain beside being a pleasant sign of nature can sometimes cause slight disturbance especially when you are traveling or are on a move. But, it’s appealing aroma or otherwise known as “Petrichor” cannot be ignored in any case. The demand of the fragrance has been increasing in the perfume industry.

This can be noticed from the rising customers worldwide on various e-commerce platforms. Whatever is the case, it is clear that this characteristic smell is part of our lives and is a result of complex changes which produce a strong yet pleasant aroma coming from the wet earth and air breeze.

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