![]() When clouds form, however, they block out some solar radiation and thereby have a net effect of cooling the air.Nozzle of a mounted aerosol fire suppression systemĬondensed aerosol fire suppression is a particle-based method of fire extinction. The condensation process, however, releases latent heat, which may help the cloud to grow upward, by warming the humid air, causing it to rise, or, conversely, may evaporate the clouds as the warmed air falls below the saturation point and is able to absorb more water vapour. If the cooling continues beyond the point of saturation, and provided there are sufficient condensation nuclei in the air around which tiny cloud or fog droplets can form, the excess moisture will condense out of the air as cloud or fog droplets or various forms of precipitation at the Earth’s surface. This atmospheric cooling can be brought about in a number of ways, as by the arrival of a cooler air mass or by the movement of an air mass up a mountain side. Unsaturated air can become saturated in three ways-by evaporation of water into the air by the mixing of two masses of air of different temperatures, both initially unsaturated but saturated as a mixture or, most commonly, by cooling the air, which reduces its capacity to hold moisture as water vapour sometimes to the point that the water vapour it holds is sufficient for saturation. Saturated air, for example, has a relative humidity of 100 percent, and near the Earth the relative humidity very rarely falls below 30 percent. Relative humidity is the water-vapour content of the air relative to its content at saturation. When a volume of air at a given temperature holds the maximum amount of water vapour, the air is said to be saturated. ![]() At -40 ☌ (-40 ☏), however, it can hold no more than 0.2 percent. At 30 ☌ (86 ☏), for example, a volume of air can contain up to 4 percent water vapour. The water-vapour content of the atmosphere varies from place to place and from time to time because the humidity capacity of air is determined by temperature. Water vapour enters the atmosphere primarily by the evaporation of water from the Earth’s surface, both land and sea. What’s the Weather Today? Fact or Fiction SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history. ![]() #WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives. ![]()
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