For years, the smell of rain after a dry spell has continued to entice people with its fresh and sweet scent. The aroma is so pleasing to the senses that air fresheners, candles and colognes have incorporated the smell in their products. Now, experts have finally discovered how this smell comes to fill the air.
According to Mashable, scientists from the Massachusetts Instutute of Technology conducted a study on how people smell rain in the air. Their research showed that the scent, also known as "petrichor," comes from tiny bubbles that drift into the air after it escapes the rain particles that hit porous surfaces.
A report by IFL Science detailed this process further. Plants and other organisms found in the ground often secrete oil. During dry spells, these organisms and plants secrete more oil. With a longer period of drought comes more oil build-up in the ground. When water comes in contact with this oil build-up during rain, it gets released in the air through tiny bubbles.
Cullen Buie, assistant professor for mechanical engineering in MIT, along with Youngsoo Joung, conducted the experiment to observe this mechanism, noted Science 20. The duo handled an estimated 600 experiments done on 28 different kinds of surfaces with 16 of it from soil samples and 12 from created materials. To better observe the process, they set up a high-speed camera system to capture the droplets' contact on the surface.
The results they got showed that the raindrops are flattened soon as it hit the ground. At the same time, tiny bubbles rise up from the contact and spread in the air. However, the kind of surface and speed of the drop affects the way the bubbles or "frenzied aerosols" as the researchers called it, are dispersed.
According to Joung, "We found you can control the speed of aerosol generation with different porous media and impact conditions."
Also based from their study, the team discovered that light rain produces more aerosols while heavy rain comes out with only a few, hence, the "petrichor" is more obvious during light to moderate rains than during a heavy downpour.
According to the Smithsonian, two Australian scientists, Isabel Joy Bear and R.G. Thomas, coined the term "petrichor" in 1964. The research discovered where the scent comes from, which was indicated then as oils from plants and organisms in the ground. But the said research did not include an explanation on how the oils are dispersed into the air. Buie believes that their study has finally uncovered the process.
"Interestingly, they don't discuss the mechanism for how the smell gets into the air. One hypothesis we have is that the smell comes from this mechanism we've discovered," noted Buie.
