The Science Behind The Fresh Smell Of Rain

Reports that Covid-19 robs you of your sense of smell has led me to appreciate those natural aromas that we so easily take for granted. The smell of newly cut grass, the warm yeasty smell of fresh bread, and the fresh fragrance that ushers in the rain.
As those great big raindrops touch the earth, they produce a very distinctive smell. This is called “petrichor” and it’s caused when the water hits the soil and releases chemical compounds. A recent MIT study used high-speed cameras to show that when rain hits the soil it releases aerosols into the surrounding atmosphere.
This infographic explains the science behind the smell of rain. These include the earthy aroma emitted by the bacteria in the soil. These bacteria decompose biological materials which then feed the surrounding flora and fauna. In the process, the bacteria emit geosmin which is what we smell. The decomposition process speeds up when there is moisture around–hence the enhanced fragrance.
In addition to the smell of geosmin, plants secrete oils during periods when there is no rain and when the rain comes down oxidization releases the aromatics from the surrounding soil. This is why rain smells so much sweeter after a long dry spell.
And, then there’s the clean fresh smell of ozone that comes along with the occasional thunderstorm.

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