How a bursting raindrop makes the smell of rain

The smell of rain comes from bursting bubbles, not the rain itself. Scientists at MIT used high-speed cameras to film raindrops hitting 28 different surfaces. They tried 12 man-made materials and 16 types of soil. When a raindrop lands on porous ground, it traps tiny air pockets. Those bubbles shoot up and burst at the drop's surface. They fling out hundreds of tiny droplets within microseconds. These droplets carry plant oils and bacterial compounds from the soil. That is what sprays the earthy smell into the air. Light to moderate rain made the most droplets. Sandy and clay soils released the most scent. The study was published in Nature Communications in January 2015.

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