Pollutant Information: Sulphur Dioxide 

About Sulphur Dioxide

Category: Air pollutants

Sulphur dioxide (SO2 expressed as SOx) has long been recognized as a pollutant because of its role, along with particulate matter, in forming winter-time smog. Studies indicate that SO2 causes nerve stimulation in the lining of the nose and throat. This can cause irritation, coughing and a feeling of chest tightness, which may cause the airways to narrow. People suffering from asthma are considered to be particularly sensitive to SO2 concentrations.

Fuel combustion accounted for 91% of UK SO2 emissions in 2021 with the main sources being the combustion of coal, heavy fuel oil and petroleum coke (a solid fuel produced in crude oil refineries). Sulphur dioxide emissions from fuel combustion originate from the sulphur contained in the fuel being burnt, and coal, coal-based smokeless fuels, fuel oil and petroleum coke all have a high sulphur content relative to other fuels.

Since 1990, SO2 emissions have declined by 96%. This has occurred due to a steady decline in the use of coal and fuel oil in all sectors of the UK economy, plus improved abatement technology, most notably the fitting of flue-gas desulphurisation (FGD) systems at coal-fired power stations. Across all sources, emissions from use of coal have reduced by 99% between 1990 and 2021 and for fuel oil the figure is 99%. Emissions from the use of coal to generate electricity have decreased by 99.8% since 1990, and emissions in 2021 were down by 30% from the previous year due to coal consumption. Fuel oil is no longer used in significant quantities at power stations and emissions in 2021 were just 0.1% of the emission in 1990. In recent years, as the consumption of coal and fuel oil in the UK has dwindled, the percentage contribution of petroleum coke to the UK inventory has increased. Emissions from the use of petroleum coke were just 1% of the UK total in 1990 but grew to 28% by 2021, while for coal the corresponding figures are 69% of emissions in 1990 and 28% in 2021 and for fuel oil, the figures are 19% in 1990 and 6% in 2021. Petroleum coke formed in UK refinery processes is burnt to recover energy while imported petroleum coke is used as a fuel for certain industrial processes and as a residential sector fuel, for example in smokeless fuels.

More stringent legislation on the sulphur content of liquid fuels used in transportation has also helped to reduce emissions, and emissions from gas oil and road diesel in 2021 have decreased by 95% since 1990.

Emissions of SO2 will need to be reduced by 25% based on the 2021 total to meet the 2030 National Emission Ceilings Regulations and Gothenburg Protocol targets.

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Time series graph

Notable events

Start year End year Sector Information Impact
1985 2009 Combustion in Energy and Transformation Industry Power Station Flue Gas Desulphurisation (FGD) abatement equipment installed. By 2008 FGD contributed between 1/4 and 1/3 of total emissions reductions from power stations. Decrease in emissions
1984 1985 Combustion in 'Industry', 'Residential', 'Commercial' 1984 miners' strike led to a significant decrease in the use of coal for combustion in electricity generation. A noticeable dip in emissions from coal-fired combustion sources in 1984 but increase in use of alternative fuels (e.g. Oil) and resulting emissions of pollutants (Cadmium & Lead). Decrease in emissions
1981 2018 Combustion in 'Industry', 'Residential', 'Commercial' Restriction on use of smoke producing fuels in urban areas, switch from coal and oil to natural gas and from 2006 reduction in sulphur content of gas oil Decrease in emissions
2009 2012 Industrial process The economic downturn has caused significant reductions in energy demands and many industries have made cut backs or closures, resulting in reduced emissions. Decrease in emissions
2010 2012 Public Electricity and Heat Production As a result of the economic downturn the drive to cut energy costs has resulted in an increase in solid fuel use, particularly in 2012 some coal-sensitive pollutants have seen a significant rise in coal burning emissions. Increase in emissions
2012 2018 Combustion in energy and transformation industry Coal combustion in power stations has fallen by over 40% Decrease in emissions
2020 2020 Road transport, aviation and railways Because of measures in place during the COVID-19 pandemic, SO2 emissions from road transport, aviation and railways in 2020 were 25%, 60% and 6% lower than they had been in 2019 respectively. Decrease in emissions
2021 2021 Road transport As a result of easing COVID-19 restrictions, SO2 emissions from road transport 2021 were 14% higher than they had been in 2020 Increase in emissions