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CINDY DAY: Have you ever 'smelled' the rain?

Near Blomidon, N.S.,  just as the rain clouds were clearing, but Cape Blomidon was still lost in the fog.
Near Blomidon, N.S., just as the rain clouds were clearing, but Cape Blomidon was still lost in the fog. - Phil Vogler

Not long ago, I wrote about the distinctive smell that comes before a rain or, more specifically, before a storm rolls through.

Cindy Day
Cindy Day

That unique, hard-to-pinpoint scent in the air is the pleasant aroma of ozone, or a form of oxygen.

Since that column appeared, many have asked about the smell after it rains. Once the rain has started to fall, you might have noticed other smells wafting through the air. When it comes to rain smells, there are a few categories.

One category is post-precipitation scents and it has a name: petrichor. It occurs when airborne molecules from decomposing 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. Then, when the rain comes, the “after-the-rain” scent is released.

Another after-the-rain smell is one that can be described as a musty-earthy smell. Well, that smell also has a name: it’s called geosmin. Geosmin means “earth smell” in Greek and it’s a metabolic byproduct of bacteria or blue-green algae. It can be a comforting call to gardeners eager to dig in the dirt, but there is a darker side to this one: it has been known to contaminate wine or drinking water. You can also find geosmin in beets and freshwater fish like catfish and carp, where it concentrates in the fatty skin. Experts have found that humans are very sensitive to geosmin and can detect it at levels as low as five parts per trillion. If you’re not a fan of that earthy smell, you can cook the fish or beets with vinegar or lemon juice;  acids render the geosmin odourless. 

So there you have it: that after-the-rain smell is not in your head, it’s in the soil, some fish and those delicious beets.

There’s rain on the way June 24 and 25. Might I suggest you give the air the sniff test?  Let me know what you think. 

Cindy Day is the chief meteorologist for SaltWire Network.

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