MIT researchers have discovered that light can cause not only heating but also evaporation in a variety of natural and synthetic water surfaces. The discovery could have implications for climate modeling and lead to innovations in solar energy and water purification technologies.
This is the most basic of processes; water evaporates from the surface of oceans and lakes, fog burns off under the morning sun, and salt pools dry out, leaving solid salt behind. Vaporization is everywhere and people have been observing and using it throughout their lives. But again, it turns out we’ve been missing a big part of the picture all along.
Discovery of light-induced evaporation
In a series of meticulously precise experiments, a team of MIT researchers has shown that heat is not the only thing that causes water to evaporate. Light hitting the water surface at the point where air and water meet can break off water molecules and carry them into the air, causing evaporation in the absence of any heat source.
A surprising new discovery can have a wide range of important consequences. This could help explain mysterious measurements over the years of how sunlight affects clouds, and could therefore influence calculations of the impact of climate change on cloud cover and precipitation. This could also lead to new ways of designing industrial processes, such as desalination using solar cells or drying materials.
A newly discovered phenomenon
The new study builds on research published last year that described this new “photomolecular effect” only under very specific conditions, on the surface of specially prepared hydrogels immersed in water. In the new study, the researchers show that the hydrogel is not necessary for the process; This occurs on any water surface exposed to light, whether it is a flat surface such as a body of water or a curved surface such as a cloud vapor droplet.
Because the effect was so unexpected, the team tried to prove its existence with as much different evidence as possible. In this study, they report 14 different tests and measurements they made to establish that water does indeed evaporate, that is, water molecules fly off the surface of the water into the air, only by light, not by heat, as has long been thought. is the only mechanism involved.
Solve the cloud puzzle
This discovery could solve an 80-year-old climatology mystery. Measurements of how clouds absorb sunlight generally show that clouds absorb more sunlight than normal physics would predict. The additional evaporation caused by this effect may explain the long discrepancy, which has been the subject of debate since such measurements are difficult to make.
“These experiments are based on satellite data and flight data,” Chen explains. “They fly the plane above and below clouds and have data based on ocean temperature and radiation balance. And they all concluded that the clouds absorbed more than the theory predicted. However, due to the complexity of clouds and the difficulty of making such measurements, researchers debate whether such discrepancies are real. “And what we found suggests that there is another mechanism of cloud absorption that has not yet been explained, and that mechanism may explain the discrepancies.”
Chen said he recently spoke about this phenomenon at an American Physical Society conference, where a physicist who studies clouds and climate said they had never considered such a possibility, which could affect calculations of the complex effects of clouds on climate. The team conducted experiments using LEDs shining on an artificial cloud chamber and observed that the fog became warmer; This should not have happened because water is not absorbed in the visible spectrum. “Such warming can be more easily explained on the basis of the photomolecular effect,” he says.
Among a wealth of evidence, Lv says that “the flat region in the air temperature distribution over warm water is the easiest region for humans to breed.” This temperature profile, he says, is “a signature” that clearly indicates the effect.
Source: Port Altele
