Is a humidity of zero percent possible?
Given the Earth’s present climate and geography, it’s an impossibility. Water vapor is always present in the air, if only in trace amounts, and so it is impossible to have a relative humidity of exactly zero percent. All of the Earth’s surface contributes water vapor to the atmosphere: water evaporates from open water (0ceans, lakes, rivers), from ice and snow fields and from plants. Once water vapor is airborne, wind distributes it everywhere, even across arid deserts. The world’s lowest relative humidity value occurred at Safi-Abad Dezful, in western Iran, on June 20, 2017, when the temperature hit 115.7 degrees with a dewpoint of -27.8 degrees, giving a relative humidity of 0.36 percent.