Public electricity generation is one of the major sources of RSP emission. It contributed to 28% of total emission in 2007. The import of nuclear electricity from Daya Bay of the Mainland in 1994 and the use of natural gas for power generation since 1995 had resulted in a downward emission trend. The increase in 2003 and 2004 was due to the increased power generation from coal-fired units. Since 2005, emission caps had been set in licences of the power plants and the emissions in 2007 decreased by 14% from 2006.