Crazy Slo-Mo Video Explains Why Rain Has That Distinctive Smell

Here's Why Rain Has That Distinctive Smell

Have you ever smelled that distinctive, sweet aroma that lingers after it rains?

Scientists call it "petrichor," and since the 1960s, they've believed it comes from oils and chemicals that are released when raindrops hit the ground.

Now, for the first time, scientists at MIT have used high-speed cameras to show how that "rain smell" gets into the air -- just check out the video above for a look at their footage.

“It’s a very common phenomenon, and it was intriguing to us that no one had observed this mechanism before," Dr. Cullen R. Buie, a professor of mechanical engineering at the university and one of the researchers, said in a written statement.

For the research, Buie and post-doctoral researcher Youngsoo Joung filmed raindrops as they hit a variety of surfaces, including 16 different soil samples. They also varied the intensity and speed of the "rainfall"--from light to heavy--by dropping the water from different heights.

They found that when a raindrop hits a porous surface, tiny bubbles form inside the droplet. These bubbles grow bigger and float upward--like bubbles in a glass of champagne. When the bubbles reach the surface, they burst and release a "fizz of aerosols" into the air.

Buie and Jung believe these aerosols carry the rainlike aroma, along with viruses and bacteria from soil.

They also noticed that light and moderate rain, which falls at a slower rate, tends to produce more aerosols compared to the heavy rain--which explains why petrichor is more common after a light rain.

“Until now, people didn’t know that aerosols could be generated from raindrops on soil,” Joung said in the statement. “This finding should be a good reference for future work, illuminating microbes and chemicals existing inside soil and other natural materials, and how they can be delivered in the environment, and possibly to humans.”

The research was published on Jan. 14 in the journal Nature Communications.

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