Smog is a type of air pollutant.
The word smog was coined in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog.
The word was then intended to refer to what was sometimes known as pea soup fog a familiar and serious problem in London from the 19th century to the mid 20th century.
This kind of smog is caused by the burning of large amounts of coal within a city; this smog contains soot and smoke sulphur dioxide etc.
The atmospheric pollution levels of Los Angeles Beijing Delhi Mexico City Chandrapur and other cities are increased by inversion that traps pollution close to the ground.
It is usually highly toxic to humans and can cause severe sickness cancer shortened life or death.