The weather
is grey and your mood is blue. It starts
to rain. You step outside in the first downpour of the season, after a long dry
spell: the sweet, fresh, earthy smell of rain just lifts up your spirits. The
aroma makes you feel happy and rejuvenated.
Do you know?
The smell of rain has its own scientific name – ‘Petrichor’.
The word
derives its ethereal essence from the Greek mythology- ‘PETRA’- which means
stone and ‘ICHOR’ - refers to the fluid that flows like blood in the veins of
the Gods.
History -
Back in 1964, a pair of Australian scientists (Isabel Joy Bear and R. G. Thomas)
began the scientific study of rain’s aroma in earnest with an article in Nature
titled “Nature of Argillaceous Odor.” In it, they coined the term petrichor to
help explain the phenomenon.
What Makes
Rain Smell So Good?
1. The
contribution of plants – The plants produce certain oils such as Palmitic acid
and Stearic acids, particularly when there is a relatively long spell of dry
weather. These are produced to inhibit growth and minimize competition for
water. These oils collect in the soil and in rocks; rain then causes a range of
smaller, volatile compounds to form within them. When a raindrop hits a porous
surface it traps tiny pockets of air. These bubbles then speed upward, like
bubbles in a glass of champagne, before breaking the drop's surface and
releasing microscopic particles, called aerosols which contain these oils
dispersed in them, giving the rain its characteristic smell.
2. Blame it
on the Bacteria –Certain bacteria, particularly Streptomyces and Actinomyces,
produce spores during very dry periods. The longer the soil goes without rain,
the more the number of spores. The smell isn’t actually caused by the spores
themselves, though. Rather it’s caused by a chemical excreted during the
production of the spores known as “Geosmin.” Geosmin is an organic compound
with a distinct earthy flavor. It is what gives beets that distinctive “earthy”
taste. The human nose is extremely sensitive to Geosmin and is able to detect
it at concentrations as low as 5 parts per trillion. If you’ve ever drank water that tasted
“muddy,” but was otherwise seemingly clean, there is likely some Geosmin in
your water.
3. Odour of
Ozone- Ozone or O3 is made up of three oxygen atoms bonded together. An
electrical charge can split oxygen and which then interacts with other oxygen
molecules in the atmosphere to produce ozone. Ozone has a sharp odour. It’s
unstable in the lower atmosphere, and is usually only found higher up –
however, the downdrafts of wind produced by a storm can sweep it down from the
higher atmosphere, making it possible for us to detect it, and giving the that
‘pre-rain’ smell.
Studies
reveal that the smell of rain can literally relieve stress and improve your
mood by over 60%. The smell apparently is so powerful that neuroscientists came
up with a perfume that matches it so the earthiness can also reap the benefits
of the feel-good scent.
Next time it rains try inhale the scent and brag
about it that now you know the reason behind the aroma and your elated mood.
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