Línfén (simplified Chinese: 临汾; traditional Chinese: 臨汾) is a prefecture-level city in southern Shanxi province, People's Republic of China. It is situated along the banks of the Fen River. It has an area of 20,275 square kilometres (7,828 sq mi) and according to the 2010 Census, a population of 4,316,612 inhabitants. It was known as Pingyang (平阳) during the Spring and Autumn Period. According to a study by Blacksmith Institute based in New York City in 2006, Linfen is the most polluted city in the world.