Smog

Smog, a portmanteau of smoke and fog coined in the early 20th century, is a type of intense air pollution composed of nitrogen oxides, sulfur oxide, ozone, smoke, and other particulates. It is produced by coal combustion, vehicle emissions, agricultural emissions, industrial emissions, forest fires, and the photochemical reactions among these emissions; the term was originally applied to the smoky, opaque fog known in London from the 19th century to the mid-20th century as a London particular or London fog. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/