Grandpa Used to Say ‘I Smell Rain Moving In’ – Could He?
Growing up I would always hear older people, like my grandpa, say "It smells like rain." I never kept detailed records of when I'd hear people say that and when it would rain, so I don't have any data to consult to see if it was true. But, it is one of those things that seems like it could be true. Like the way, Bill in the movie Twister was a human barometer and could feel the storms coming.
Yea, I've seen that movie way too much.
Anyways, with the resources of the internet at my fingertips, I decided to dig in and see if there was, in fact, some scientific basis to the idea that one could smell the rain coming. Or if it is an old wives tale.
Turns out, yes you can smell the rain. There are a three common rain smells according to Scientific American. There's a distinct 'before the rain starts' smell, one from when rain is falling, and one after you're wet.
Before the rain starts, the wind can whip up the smell of ozone. This scent is likely blown down from the clouds after being created by lighting.
Before the rain begins, one of the first odors you may notice as winds pick up and clouds roll in is a sweet, pungent zing in your nostrils. That's the sharp, fresh aroma of ozone—a form of oxygen... An electrical charge—from lightning or a man-made source such as an electrical generator—splits atmospheric nitrogen and oxygen molecules into separate atoms. Some of these recombine into nitric oxide, and this in turn reacts with other atmospheric chemicals, occasionally producing a molecule made up of three oxygen atoms—ozone, or O3. (Most atmospheric oxygen is made up of two atoms—O2.) The scent of ozone heralds stormy weather because a thunderstorm's downdrafts carry O3 from higher altitudes to nose level.
Once the rain starts, it can create a smell known as 'petrichor.' It comes from the rain disturbing molecules on dry surfaces and launching them into the air. The wind will then carry them to your nose. Trees, plants, concrete, and asphalt are the usual sources for these molecules.
[Petrichor] 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 rains came, the redolent combination of fatty acids, alcohols and hydrocarbons is released.
After the rain, there is often an "earthy-musty" smell caused by bacteria or algae. I think this smells like what I smell at a lake, so I'm guessing it comes from a similar source.
This is the aroma of geosmin, a metabolic by-product of bacteria or blue-green algae.
Watch this video from The Weather Channel for more: