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A close-up view of water droplets forming fog. Those outside the camera lens's depth of field appear as orbs. Fog forms when the difference between air temperature and dew point is less than 2.5 °C (4.5 °F). [6] [7] Fog begins to form when water vapor condenses into tiny water droplets that are suspended in the air.
[citation needed] One main difference between mist and fog is visibility. [1] The phenomenon is called fog if the visibility is 1 km (1,100 yd) or less. In the United Kingdom, the definition of fog is visibility less than 100 m (330 ft) on the surface for driving purposes, [2] while for pilots the distance is 1 km at cruising height. Otherwise ...
Likewise, warming air decreases the relative humidity. Warming some air containing a fog may cause that fog to evaporate, as the droplets are prone to total evaporation due to the lowering partial pressure of water vapour in that air, as the temperature rises. Relative humidity only considers the invisible water vapour.
In the air, the condensed water is called either fog or a cloud, depending on its altitude when it forms. If the temperature is below the dew point, and no dew or fog forms, the vapor is called supersaturated. This can happen if there are not enough particles in the air to act as condensation nuclei. [5]
Since the saturation vapor pressure is proportional to temperature, cold air has a lower saturation point than warm air. The difference between these values is the basis for the formation of clouds. When saturated air cools, it can no longer contain the same amount of water vapor.
Water in Earth's atmosphere is not merely below its boiling point (100 °C), but at altitude it goes below its freezing point (0 °C), due to water's highly polar attraction. When combined with its quantity, water vapor then has a relevant dew point and frost point, unlike e. g., carbon dioxide and methane.
Mist in an airplane cabin often gets mistaken for smoke and can cause anxiety or panic among passengers. Here’s the science behind it and why it’s perfectly harmless.
Usually, within the lower atmosphere (the troposphere) the air near the surface of the Earth is warmer than the air above it, largely because the atmosphere is heated from below as solar radiation warms the Earth's surface, which in turn then warms the layer of the atmosphere directly above it, e.g., by thermals (convective heat transfer). [3]