The-fog is a type of fog that forms when warm, moist air comes into contact with a cooler surface. This type of fog is commonly found along coastlines when moist sea breezes from tropical regions blow over areas of land where the ground is cool.
In inland areas, radiation fog can form in the early morning when cool air from the ground meets warm, dry air above. The cold air sinks below the dew point temperature and water vapor condenses around dust particles to form fog.
This is a regular occurrence in north western Europe and also in coastal areas of North America. When warm, moist air from offshore – the North Atlantic and the waters around the British Isles – moves towards a colder land surface or shallow water surface it cools below the dew point temperature.
Upslope fog can be seen on the top of mountains when moist air comes into contact with the slope of the mountain. As the air rises, it cools because of adiabatic cooling and the drop in pressure as the altitude increases.
Smog can be formed when pollutants (soot, sulphur dioxide) in the air come into contact with the surface of the air. It is a common type of fog in industrial areas, especially where coal is burnt for heat and electricity.
Smog can reduce visibility to under a quarter of a mile and it can be very dangerous. It can also make it difficult to see traffic and road signs. It can be compared to mist, but is denser and has more of an impact on visibility.