A team of scientists from the Massachusetts Institute of Technology (MIT) has identified the mechanism that releases the particular wet smell that we notice when it rains . The finding has been published in the journal Nature Communications .
For their research, the experts conducted nearly 600 experiments on 28 different types of surfaces including the soils throughout the MIT campus, along the Charles River and even the sandy soil of Nahant Beach (Massachusetts). Once in the lab, they measured the permeability of each soil sample by pouring the material into long tubes to start with and then adding water to the bottom of each tube while taking measurements of the rate at which the water was rising through the soil. . They found that the more permeable the soil was, the faster the water rose.
On the other hand, they deposited individual water droplets on each of the surfaces under study, simulating various rain intensities. The experiment revealed that the greater the droplet release, the faster its maximum speed .
Capturing the raindrops at the moment of impact with high-speed cameras they discovered a mechanism not seen before: when a drop of water hits a surface, it begins to flatten and simultaneously small bubbles begin to rise before bursting into the air. Thus, depending on the speed of the drop and the properties of the surface, a frenzied cloud of aerosols disperses through the air, causing this particular wet smell. The conclusion was that more aerosols are produced when the rain is light, but they are expelled in greater numbers when it rains heavily .
‘Frantic means it can generate hundreds of aerosol droplets in a short time, for a few microseconds. And we found that the rate of aerosol generation can be controlled with different porous media and impact conditions, ”explains Youngsoo Joung, co-author of the study.
The researchers clarify that, in natural environments, aerosols can carry aromatic elements , along with bacteria and viruses that are stored in the soil. These aerosols are released during rain and spread by the force of the wind.
” This finding should be a good reference for future work , illuminating existing microbes and chemicals inside soil and other natural materials, and how they can be delivered into the environment, and possibly humans,” Joung adds.
