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Mist and fog are a mass of tiny water droplets suspended in the lower layers of the atmosphere.

Fog is denser than mist i.e. has more moisture.

Both hinder visibility although fog reduces visibility to less than a kilometre.

When fog mixes with smoke its called smog.

How They Form

  • Moist air cools below dew point.
  • Condensation takes place.
  • The resultant water droplets remain suspended in the air.

Types of Fog

  1. Radiation Fog
  • Type formed when moist air is cooled below dew point as a result of intense radiation on the ground at night.
  1. Advection Fog
  • Type formed when moist air from the sea moves horizontally over a cold surface e.g. snow covered ground.
  1. Orographic/Hill/Upslope Fog
  • Type formed when moist air is cooled after climbing a hill or mountain.
  1. Evaporation Fog
  • Type formed when water vapour is added to cold air that is already near saturation causing excess water vapour to condense and form fog.
  1. Frontal Fog
  • Type formed when warm moist air is cooled from below as it rises over a cold air mass.
  1. Steam Fog
  • Type formed when moist air passes over the surface of a much warmer fresh water body.
  • The warm water is cooled from above and condensing water vapour forms fog. It appears to be steaming.
  1. Ice Fog
  • Type formed when water vapour is converted directly into ice crystals when temperatures are below freezing point.

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