In simple terms, fog is cloud at ground level. It can cover vast areas, vary in density and thickness, and, like clouds, comprises of a various types. Broadly speaking, fog forms when the saturation point of the air near the ground is reached - this means that the air contains the maximum amount of water vapour that it can hold for that specific temperature and pressure, therefore this invisible water vapour condenses into liquid water droplets with an average diameter between 0.
In order for fog to form, dust, sea salt or other air pollutants must be present. Water vapour condenses onto these microscopic particles and forms fog — in the same way as clouds and ultimately rainfall is formed. Thickest, or densest, fog occurs in areas where there are many microscopic particles, such as industrial areas or over the sea.
Of course, thick fog can obscure even the largest of structures. Mist and fog are often used interchangeably - and they are closely related - but there is a key difference which depends on how far you can see through them. This is called visibility and forecasting it is very important not only for shipping and aviation, but also for the public, as driving conditions are affected.
The more water droplets there are suspended in the air, the lower the visibility. The term fog is used when visibility is less than 1 km. This distinction is agreed internationally for aviation purposes. However, for the general public, forecasters frequently use the term fog to describe when visibility is less than m. Mist typically dissipates more rapidly, even with slight winds. Interestingly, it can also describe your breath on a cold day.
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You cannot download interactives. A volcano is a feature in Earth's crust where molten rock is squeezed out onto the Earth's surface. Along with molten rock, volcanoes also release gases, ash, and solid rock.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. If the mist is a hazardous material, eye and skin contact as well as inhalation is a danger.
You can change your workplace practices to reduce or eliminate the formation of mists in the first place, use engineering controls such as local exhaust ventilation , and wear appropriate personal protective equipment to reduce these risks. Also recognize that when a mist droplet hits a solid surface it will usually wet the material, compounding your problems. See also : boiling point , dust , engineering controls , fume , vapor , ventilation. Additional definitions from Google and OneLook. Entry last updated: Sunday, February 23, This page is copyright by ILPI.
Unauthorized duplication or posting on other web sites is expressly prohibited. Learn more. Asked 10 years, 2 months ago. Active 3 years, 8 months ago. Viewed 29k times. Improve this question. David Z Obviously there is the concept of humidity, which formalizes the capacity of air to hold water at a certain temperature. Steam, however, requires being over the boiling point to be called "steam". I wonder about the physics of how steam changes into humidity and the molecular energy distribution changes through the process.
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