Scents of seasonal rains after a dry period

I’ve never thought about comparing the seasonal rains in two these periods of time. It just crossed my mind when I was coming home after a scattering rain in the middle of April – the first month of the rainy season in Vietnam. The smell and space of streets after rains are totally different from Saigon and my hometown. In my rural hometown, when the rain finished, the life pace of all living creatures (including humans, trees and animals) seems slower and more silent than it is usual.

Fortunately, when my living city came with the rainy season, Givaudan unveiled Geogaia™ – a blend that reproduces the scent of Petrichor, the smell that comes from the ground when rain falls after a dry period, which makes me more curious about the smell of nature after rain.

I found that:

Petrichor

Petrichor is the term coined by Australian scientists (Isabel Joy Bear and Richard Thomas ) in 1964 in their article “Nature of Argillaceous Odour”, to describe the unique, earthy smell associated with rain. It is caused by the water from the rain, along with certain compounds like ozone, geosmin, and plant oils. The word was coined from Greek Petros, meaning “stone”, and ichor, meaning “the fluid that flows in the veins of the gods”.

Geosmin

Actinomycetes, a type of bacteria found in soil, secrete a compound called geosmin, which is released from the soil into the air by raindrops. Geosmin in the air can be detected by the human nose at less than 5 parts per trillion.

From: https://www.acs.org

“It’s a really potent material and it smells just like the concrete when the rain hits it,” said perfumer Marina Barcenilla. “There’s something very primitive and very primal about the smell.”

Volatile plant oils

Stearic acid and palmitic acid are common plant oils. They are fatty acids, long hydrocarbon chains with a carboxyl group on one end and a methyl group on the other. During dry weather, plants produce compounds that accumulate in between rocks and soil. When it rains, these compounds are released into the air to add to the earthy smell of petrichor.

From: https://www.acs.org

Besides, rain may also break dry plant material releasing chemicals because seasonal dry periods can slow down plant metabolism, with renewed rainfall giving it a kick start and causing plants to release a pleasant scent.
That contributes to the delight scent of Petrichor.

Scents of Seasonal rains now and in my childhood

When coming dorm after working in the lab all day, I recognize that Saigon streets after rain are different from those in my hometown. The hustle and bustle of city life is still happening even whether the weather is hot or cold, rainy or sunny. People still are busy with their concerns to make a living.

In my rural town, after a rain shower, almost things from humans to nature seems to take a break to enjoy the valuable time of delight and cool weather. The winds stop blowing, and rees or flowers stop swaying. Everything seems to settle down. People there usually avoid traveling on the streets during heavy rains or strong thunders.

Unlike my childhood hometown, the life pace of Saigon is always bustling. During or after rain, people still work and travel a lot in the streets, outdoor activities are happening even it’s raining heavily (of course, some food street stalls have to stop selling food because no owners want their well-prepared products wet and cooled by the bad weather).

Scentmefree._