Probing water's skin

From the wind-whipped surface of the open ocean, to trillions of tiny water drops in clouds, the air-water interface—water's skin— is the site for crucial natural processes, including ocean-atmosphere exchange and cloud acidification. The air-water interface has even been postulated as the cradle of life. However, factors such as its subnanometer size and dynamic nature, render the investigation of interfacial wanter a daunting task.