Coal pollution mitigation emissions of sulfur dioxide or oxides of nitrogen associated with the utilization of coal in the generation of electricity." Before being adopted in this fashion, historically "clean coal" was used to refer to clean-burning coal with low levels of impurities, though this term faded after rates of domestic coal usage dropped. The term appeared in a speech to mine workers in 1918, in context indicating coal that was "free of dirt and impurities." In the early 20th century, prior to World War II, clean coal (also called "smokeless coal") generally referred to anthracite and high-grade bituminous coal, used for cooking
Coal mining in the United Kingdom the United States. Of the coal mined in the UK in 2016 all was from open-cast coal mines. Employment in coal mines fell from a peak of 1,191,000 in 1920 to 695,000 in 1956, 247,000 in 1976, 44,000 in 1993, and to 2,000 in 2015. Almost all onshore coal resources in the UK occur in rocks of the Carboniferous age, some of which extend under the North Sea. Bituminous coal is present in most of Britain's coalfields and is 86% to 88% carbon. In Northern Ireland, there are extensive deposits of lignite which is less energy-dense based on oxidation (combustion)