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Photos show how rain smells

Bacteria and oil the aroma of rain

When a raindrop hits dirt, odors are released by aerosols in a three-step process, consisting of bubble formation, bubble growth, and bubble bursting. (mage courtesy of Youngsoo Joung)

JACKSONVILLE, Fla – Smell the rain...you are actually sniffing the byproducts of plants, dirt, bacteria, and ozone and not the rain itself.

The smell of rain this time of year can be so strong your nose often senses the rain before your eyes. 

Bacteria called, Streptomyces, make a molecule that humans can detect as a the familiar damp earth sent. 

The pungent aroma was given a special name called petrichor by the Australian scientists, Isabel Joy Bear and Richard Thomas, who first characterized the phenomenon in 1964. 

They recognized the distinctive scent of absorbed plant oil emitted by clay-based soils along with the pungent molecule, geosmin, which is emitted by bacteria in wet soil.

Decades later, scientists at MIT used high-speed cameras to identify how these odors get released into the air. 

Their pictures shows small aromatic aerosols shooting out from a raindrop once it hits a porous surface like dirt.

The smelly aerosols were higher in lighter rain because the higher impact speed of heavy rain, does not allow enough time to make bubbles inside the droplet that can be aerosolized. 

The smell of ozone may also be present if there is lightning. 
 


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