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Petrichor-The Smell of Rain

Weather Talk
Wednesday, March 26, 2014 - 12:16pm

There are a few oils and chemicals that combine to produce that wonderful aromatic smell when it rains on dry ground

Last night there were light showers and even a few thunderstorms that traveled through our parched desert. There was this beautiful, pleasant smell that floated through the air and lingered into the late nighttime hours. I had honestly never known the name for the amazing odor before, during and after a rainfall. I just called it, like many of us, “the smell of rain”.  A news producer I worked with, Jessica, told me a couple years back that the name for this wonderful smell is “petrichor”. So in today’s “Weather Talk” I thought I would tell you where the name came from, what are the sources that combine to produce the smell and what it signifies and is called in other cultures.

Petrichor- The word is Greek – Petro from Greek "petros" “stone” or “rock” and ichor – the golden fluid or blood flowing in the veins of the gods in Greek mythology. The term was coined in 1964 by two Australian scientists, researchers I.J. Bear and R.G. Thomas, studying the smells of wet weather while working for Australia's Commonwealth Scientific and Industrial Research Organization. They came up with the term to describe the “essence of rock”. This is officially also known as “argillaceous odor”. Bear and Thomas also wrote many other related articles through a publication called Nature.

What Causes this Smell- This smell is derived from a combination of two chemical reactions from two different sources.

First Source- Some plants, especially here in the desert, secrete oils during dry periods. When it rains, these oils are released into the air.

Second Source- of petrichor is when chemicals produced by soil-dwelling bacteria known as actinomycetes are released. This release is commonly referred to as geosmin.

These two aromatic compounds mix with each other to create the pleasant petrichor scent when rain hits the dry ground.

There is another scent that is produced with rain, ozone. Lightning, within a thunderstorm can split oxygen and nitrogen molecules in the atmosphere, and they in turn can recombine into nitric oxide. This substance interacts with other chemicals in the atmosphere to form ozone, which has a sharp smell that smells a little bit like chlorine.
Many times when you smell rain or a storm approaching, you actually smell the ozone being carried in by storm winds.

Neil Griffin, a contributor to talks about two other names for petrichor; “In Lucknow, India the scent is collected from clay-disks inundated with rain during the monsoon season. It is mixed with sandalwood oil and sold in vials as matti ka attar – earth perfume. In the parched red clay deserts of Western Australia, the Anangu people call it panti wiru, simply meaning ‘good smell’. It is the harbinger for a wave of greenness and fresh vegetative growth to overtake the desert - signaling a time of plenty. Panti wiru is associated with youth, health, fecundity, and new beginnings.”

So now you know that "Petrichor” is the smell from the combination from the oils given off by vegetation and the chemicals released by soil dwelling bacteria that is released by rain then mixes together to become a wonderful smell. We also know there may by a little nitric oxide or ozone mixed in as well. We have to thank the two Australian scientists, Bear and Thomas, for coming up with the term. I am sure it is called by many names, in many languages around the world. I have come to the conclusion that is does symbolize some sort or new start or beginning of life, definitely plant life. To myself and many others, it is just a beautiful smell that brings about good feelings and happiness.

Chuck DeBroder, Chief Meteorologist
KTSM, NewsChannel 9, NBC, El Paso, TX Chuck DeBroder NC9 @wxchuckNC9


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