Asked by: Nina Cunningham, Oxfordshire

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By definition, fog has a visibility of less than 1km, but it can get much thicker than that. The Met Office visibility scale runs down to a Category X fog, where visibility is less than 20m. If fog gets mixed with industrial pollution, it becomes smog and can be thicker still. The Great Smog of 1952 was so bad that it penetrated indoor areas and drivers couldn’t see their own headlights!

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luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.

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