The major source(s) of emissions of SOx is/are
smelting of ores
combustion of petroleum
petroleum refining
all of these
Although there are natural sources of sulphur dioxide (accounting for 35-65% of the total sulphur dioxide emissions) such as volcanoes, most anthropogenic sulphur dioxide is produced by burning fuels containing sulphur or by roasting metal sulphide ores. Thermal power plants burning high-sulphur coal or heating oil are generally the main sources of sulphur dioxide emissions worldwide, followed by industrial boilers and nonferrous metal smelters. Emissions from domestic coal burning and from vehicles can also contribute to high concentrations of sulphur dioxide.