COLUMN: What’s that smell? Is rain in the forecast?

My schedule for the day was pretty loose…this column to write, some gardening to do, and a bit of chainsaw work on a fallen oak tree. Having no idea what to write about, I went out on deck instead to see which way I should go: the half-planted garden or the distant forest?

To aid in my decision making, I took a deep breath followed by a slow release. “Hmm. It smells like rain.” And with that revelation I went back and started writing.

Rain comes with a low air pressure system, and this low pressure situation allows odor particles to move more freely. The humidity in the air also helps as the odor particles stick to the moisture droplets and from there stick to the inside of my nostrils, giving my brain time to process these field samples.

The more humid the air (read: rain), the more likely the ozone will have a chance to kick in. Ozone has three oxygen molecules (come on, I’m sure you remember that from Grade 13 Chemistry) and as such is unstable with a free oxygen molecule looking for something to do.

The raindrops themselves are an important factor in making the world smell beautiful. First, they collect ozone from high altitudes and transport the molecules downward. At the same time, the earth is bombarded by millions of raindrops that crash and crash against the terra firma.

This hitting the ground releases all sorts of odor particles that are thrown upwards. And where did these odor particles come from? Leaf mold and rotting twigs! And how does this leaf mold get there? Through the combined efforts of billions of tadpoles (also known as “snow fleas” in another season) and soil bacteria that break down organic material.

This fragrance we associate with a spring rain comes from a process called “petrichor”, a Greek word meaning “essence of rocks”. When you’re on your knees and sticking bulbs in the ground, that earthy smell you smell is petrichor.

Our noses certainly let us know when a skunk has passed by or when you’ve just walked through a patch of wild mint, but aside from these types of billboard-sized scents, our sniffer is usually regulated to just an alternative way to get air into our lungs, a task undertaken approximately 23,000 times a day.

As I rummaged through a stack of books in my room that had been bought over the years for the express purpose of expanding my literary horizons (though, for a multitude of very good excuses, not yet been read), I came across over a very interesting one. published in 1990 (the stack of books is, ahem, very large).

In her book, A natural history of the sensesDiane Ackerman approaches each of the five senses in detail, examining how they enhance our experiences of the biological world around us.

Ms. Ackerman’s chapter on the sense of smell deals with the biology and history of smells and noses; from the theory of the evolution of the nose developing before the brain, to the intimate relationship between Napoleon and Josephine over the scent of violets.

Although I found the entire book entertaining and insightful, one of Diana’s passages really hit home: “Smells detonate lightly in our memory like landmines, hidden under the weed table of many years and experiences. suddenly a complex vision emerges from the undergrowth’.

No doubt you have your own set of olfactory tripwires: grilled hot dogs; lilac at the edge of the garden; pizza fresh out of the oven, white pine on the Canadian Shield…or a distant skunk marking its territory. It’s truly amazing how one whiff of a scent or another can trigger instant mental ruminations of a place or time long ago.

It seems the rain has moved south for now anyway, leaving me with a chance to lean on a rake or fire a chainsaw. Ah yes, the smell of chainsaw exhaust… so many memories come attached to that!