I woke up to the smell of rain. I walked in my garden and breathed deeply of the scent of good Earth. Moist dewy air filled my lungs. The rain hadn’t touched the Earth but it smelled of it just the same. Where does this scent comes from?
In 1964, Australian scientists found that earthy smell, named petrichor, was from the release of chemicals in the soil after a light rain. But until now no one researched how those chemicals were released. In February two MIT mechanical engineers, Cullen Buie and Youngsoo Joung, published their research findings in the journal Nature Communications, that may explain just how those chemicals are released into the air. They were testing how water drops fall on synthetic materials and what they saw reminded them of raindrops and smell of rain. They then went on to research what happens when rain hits the ground.
The researchers filmed water droplets as they hit the soil or sandy ground. First the rain droplets flattened and tiny air bubbles formed within the droplet. These tiny bubbles fizzed up through the water droplet, rose to the top and burst through the surface, like champagne bubbles rising to the top of a wine glass. These tiny air bubbles may carry chemicals from the soil to the air. This may be the source of petrichor, the release of chemicals in the soil after a light rain. These air bubbles are called aerosols.
Researcher Joung and graduate student Zhifei Ge are continuing research to find if soil bacteria and pathogens are carried and spread through similar mechanisms which spread the those tiny aerosols which carry the smell of rain.
So, perhaps the smell of rain is the scent of the Earth carried on the wind. Rain clouds are pushed by wind across the sky and the scent of the already fallen comes along with it.
I have walked through a healthy deciduous forest as a light rain drips off deep green leaves. The distinctive scent of the forest and the goodness of the Earth is unbeatable for making me feel happy and at peace with the world.
“Rainfall can release aerosols, study finds.” NewsRX Health 1 Feb 2015:95.Student Resources in Context. Web 19 Mar 2015.
“Why rain smells like that”. Science News. 4 April 2015.