What Causes the Smell After Rain?

causes-smell-after-rain Credit: Christopher Furlong/Getty Images News/Getty Images

The smell of rain is unmistakable, and there are many factors that make up its sweet, earthy scent. It comes mostly from rainwater falling on dried materials, bacteria, or algae on the ground. There is also evidence that some people can smell the rain not only after it’s gone but before it comes.

The first key word to understanding rain’s distinct smell is petrichor, or molecules in the air that come from decomposed animal or plant materials. These particles settle on hard surfaces like rock, clay, concrete, or asphalt. When the rain comes, the petrichor releases chemicals back into the air, giving the surroundings a unique odor.

Another element that contributes to the rain’s smell is the (equally difficult to pronounce) chemical geosmin, which is a waste product of bacteria and blue-green algae. When combined with water, geosmin releases an earthy smell that is similar to soil. This smell is more prevalent in rural settings.

Biologists have studied the effect of the geosmin on behavior in both wildlife and humans. Keith Chater, an English microbiologist, has found that geosmin helps camels find nearby water sources. He even found that the bacteria that releases geosmin uses the camels as spore carriers.

But does the smell of rain carry bigger meaning for humans? Perhaps. Australian anthropologist Diana Young, who studies Aboriginal tribes, noticed that their seasonal hunting and harvesting practices were connected to the rain patterns and its odor. The Aboriginals associated the smell of rain with the color green, and they reproduced it in the form of a “perfume” using animal and plant materials.

There is also a lot of evidence to suggest that people can predict rain based on the smell of the atmosphere. Ozone tends to accumulate before a storm, thanks to natural sources as well as fertilizers and pollutants. The good part is: you’re not crazy for thinking you can do this. The bad part? You’re not really alone in your superpower.