On 4 December 1952, an anticyclone settled over a windless London, causing a temperature inversion with cold, stagnant air trapped under a layer (or "lid") of warm air.[6][7] The resultant fog, mixed with chimney smoke, particulates such as those from vehicle exhausts, and other pollutants such as sulfur dioxide, formed a persistent smog, which blanketed the capital the following day. The presence of tarry particles of soot gave the smog its yellow-black colour, hence the nickname "peasouper".[5] The absence of significant wind prevented its dispersal and allowed an unprecedented accumulation of pollutants.