You can probably smell it right now. It’s almost a tingling electric scent in the air as a storm starts to make its way through. Even after the rain has fallen, this smell transforms into a pleasant musty scent that somehow brings a nostalgic feeling to mind. What you are smelling is the molecular scent of ozone and plant compounds that are released into the air.
As a storm approaches, downdrafts from the storm drop from high into the atmosphere to the surface and spread out from under the storm. This air carries with it the tingling scent you often smell before rain. Ozone is the main cause of this smell. Since a larger concentration of ozone is present in our upper atmosphere, many downdrafts from storms pull it down to the surface. The air from a downdraft can travel for long distances even bringing the smell of rain to areas that have yet to see storm clouds. This is why many of us can predict that it will rain just by smelling the air a couple hours to a day before it actually rains. Lightning additionally, is a contributor to the release of ozone in the air. When lightning strikes, the energy splits oxygen and nitrogen molecules, the oxygen molecules then recombine into ozone. Many people describe the sharp smell of ozone to resemble the smell of chlorine.
After it rains, the smell of ozone mixes with something else, something strongly musky. what you are smelling here is called petrichor. The term petrichor, meaning “relating to rocks”, is defined as the smell that accompanies rain after a long spell of dry weather. Petrichor’s smell originates from small compounds or spores that plants release during dry weather. These compounds are released into the air and then settle on hard surfaces, in between crevices, rocks, and pavement. When it rains, the force of raindrops hitting the surface sends the spores back into the air. You may also recognize this smell if you have ever taken a walk in a moist forest or turned over soil in your garden.
The smell of rain has entered our noses for years alerting us of oncoming showers or relaxing us with nostalgic memories of cozy rainy days indoors. It’s interesting to know that plants and ozone are the makers behind it all. Next time it rains, and you notice the satisfyingly pungent smell, just think how awesome it is that you now know its origins. It’s certainly a fun scientific fact you can share with you friends and family too.
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© 2019 Meteorologist Alex Maynard
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