In 2013, the largest proportion of SOX emissions came from non-ferrous smelting and refining, representing 30% (370 kt) of total emissions, followed by the oil and gas industry, representing 25% (302 kt) of total emissions. Emissions from the use of fuel for electricity and heating contributed 24% (294 kt) of national emissions. The largest reduction in emissions between the years 1990 and 2013 was from non-ferrous smelting and refining, with an emissions reduction of 903 kt.