It's been kind of dry around here. Remember the smell of rain?
There's a name for the various smells of rain: petrichor. (For Dr. Who fans, it's also a telepathic password to the TARDIS.)
Petrichor is a combination of two Greek words --petra, stone and ichor, the fluid of the gods. According to Scientific American, it was first defined and described in 1964 by two Australian mineralogists, Isabel Joy Bear and R. G. Thomas of Australia's Commonwealth Scientific and Industrial Research Organization.
Here's how they described it---"Petrichor occurs when airborne molecules from decaying plant or animal matter become attached to mineral or clay surfaces. During a dry spell, these molecules chemically recombine with other elements on a rock's surface. When the rains come, the redolent combination of fatty acids, alcohols and hydrocarbons is released."
This complex blend of smells we associate with rain can be caused by many things---
The distinctive smell of wet earth called geosmin is caused by bacteria that grow in the soil. These bacteria can be found all over the world, which accounts for the universality of this "after the rain" smell. When the soil dries out, the bacteria produce spores, and the force of falling rain kicks them up into the air. The moisture acts as an aerosol, like a spray perfume.
Some scents come from volatile oils from plants and trees. Think of a pine forest, or the smells of lavender, rosemary or basil after a rain. Those plant oils collect on surfaces (such as rocks or sidewalks), and the rainwater reacts with the oils and minerals, producing these wonderful aromas.
Other rainy smells are caused by the chemistry of rainwater. Rain tends to be somewhat acidic, especially in more urban environments. When rainwater comes in contact with debris or chemicals on the ground, it can cause some interesting aromatic combinations. Think of soggy french fries, wet paper, gasoline!
Now, I wonder do they make one with the smell of wet earth, and city streets after the rain.....
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