Author: Antonio Da Roza
Sulphur dioxide (SO2) is formed primarily from combustion of sulphur-containing fossil fuels. In Hong Kong, power stations are the predominant emission sources of SO2, followed by marine vessels, fuel combustion and motor vehicles. 
Public electricity generation is the primary source of sulphur dioxide emission which contributed to 89% of total emission in 2007. There was a sharp reduction in 1994 due to the intake of nuclear electricity from Daya Bay. From 1995 to 1999, the use of natural gas and the installation of flue gas desulphurization units at coal-fired power generating units had further reduced the emissions. However, there was a rise in 2003 and 2004 due to increased power generation from coal-fired units. 
Since 2005, emission caps have been set for power generation and the emissions in 2007 decreased by 9% from 2006. The introduction of the use of ultra-low sulphur diesel and Euro V diesel in 2002 and 2007 also respectively led to the diminishing of the sulphur dioxide emissions from vehicles. 
High humidity aids the transfer of sulpher dioxide to sulphuric acid; sulphuric acid causes breathing problems and eye irritations.