According to the Environmental Protection Agency (EPA), which one of the following is the largest source of sulphur dioxide emissions?

Answer: D. Power plants using fossil fuels are the largest source of sulphur dioxide emissions. According to the US EPA, fossil fuel-fired power plants (particularly coal-burning utilities) are responsible for the majority of anthropogenic SO2 emissions. Coal contains varying amounts of sulphur which, when burned, oxidises to form SO2. In the US (and India): approximately 60-70% of total SO2 emissions historically come from electric utilities. The remainder comes from industrial processes, ships and other transportation. Distractors fail by magnitude: (A) Locomotives are minor SO2 sources (especially as railways shift to electric and diesel becomes cleaner). (B) Ships using high-sulphur bunker fuel WERE significant, but post-IMO 2020 regulations have cut shipping SO2 sharply; still less than power plants globally. (C) Metal extraction emits SO2 (especially sulphide ore smelting) but on a smaller scale than power plants. Source: US EPA National Emissions Inventory / Central Pollution Control Board India.