1. What is sulphur dioxide and why are emissions of it estimated?

Sulphur dioxide (SO2) is a corrosive, acidic gas which is predominantly produced from the combustion of coal or crude oil.

Direct exposure to SO2 is associated with asthma and chronic bronchitis, and can lead to irritation and constriction of the airways. SO2 emitted from coal burning played a key contributory role to thousands of respiratory-related deaths during the London smog in 1952. SO2 can also combine with nitrogen oxides and ammonia to form particulate matter (PM) which also has serious health implications (see the PM section in this release for more information on the health impacts of PM).

SO2 can also combine with water vapour in the atmosphere to form acid rain that can be transported large distances. Acid rain causes significant damage to ecosystems such as forests and freshwater habitats. Emissions of SO2 from the UK that landed as acid rain in Scandinavia in the 1970s and 1980s resulted in severe damage to habitats there. The international discussions surrounding the discovery of these transboundary impacts were the initial driver for establishing the Convention on Long Range Transboundary Air Pollution (CLRTAP), of which the UK is a founding member.

SO2 can be emitted both by natural processes, such as forest fires and volcanic eruptions, and as a result of human activities, such as the combustion of fuels. The National Atmospheric Emissions Inventory, and the statistical tables published as part of this release, only covers SO2 emissions from human activities. The information presented in this document only covers SO2 emissions from human activities within the UK.

UK emissions of SO2 from energy production have been vastly reduced in recent decades due to restrictions on the sulphur content of fuels and the closure of coal-fired power plants. However, the UK, under the CLRTAP and National Emission Ceilings Regulations (2018) (NECR), aims to reduce SO2 emissions even further: by 59 per cent compared to 2005 emissions by 2020 and in each subsequent year up to and including 2029 and by 88 per cent compared to 2005 emissions by 2030.

2. Trends in total annual emissions of sulphur dioxide in the UK, 1990 to 2023

Figure 12: Annual emissions of sulphur dioxide in the UK: 1990 - 2023

Note:

1. ‘ERC’ refers to the UK’s 2020-2029 emission reduction commitment, set out in the National Emission Ceilings Regulations (2018) and the ’2020 and beyond’ emission reduction commitment, as set out in the Convention on Long Range Transboundary Air Pollution.

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Emissions of sulphur dioxide have decreased by 97 per cent since 1990, to 111 thousand tonnes in 2023. This was driven by a decline in coal use in energy industries. Emissions from the combustion of coal in energy industries decreased by 83 per cent of 1990 levels by 2005, following which they decreased by almost 100 per cent from 2005 levels through to 2023. Stricter limits being placed on the sulphur content of liquid fuels has also reduced emissions in the long-term. Emissions of sulphur dioxide decreased by 6 per cent from 2022 to 2023 reaching the lowest level since emissions estimates have been calculated.

For emissions of sulphur dioxide, there is an annual ceiling of 321 thousand tonnes applicable between 2020 and 2029. In 2023, there were 111 thousand tonnes of sulphur dioxide emitted. Therefore, the UK met the 59 per cent emission reduction commitment for 2020 to 2029.

3. Major emission sources for sulphur dioxide in the UK

Figure 13: Annual emissions of sulphur dioxide in the UK by major emission source: 1990, 2005, 2020 and 2023

Notes:

1. ‘Industrial combustion’ refers to the burning of fuels on manufacturing and construction sites, to generate energy for industrial use, for example to drive mobile machinery or to create heat or electricity for industrial processes. This does not include emissions for public electricity and heat production, for the production of fuels, or from fuel combustion in the public sector, the commercial sector, or from the agricultural, forestry and fishing sectors.

2. ‘Energy Industries’ refers to fuel combustion in energy industries. This includes combustion in public electricity and heat production, petroleum refining and the production of other fuels.

3. ‘Domestic combustion’ refers to households burning a variety of fuels, e.g. in stoves and fireplaces

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In 2023 the three largest sources of SO2 emissions were domestic combustion (26 per cent of national total), industrial combustion (26 per cent of the national total) and fuel combustion in energy industries (26 per cent of national total).

Emissions reductions in the energy production and industrial sectors have been the strongest drivers for the long-term trend of decreasing SO2 emissions. This is due to a shift away from fuels with a high sulphur content (i.e. coal and fuel oil) to fuels with a low sulphur content (i.e. to gas and biomass-based fuels) and the fitting of flue gas desulphurisation in the remaining coal fired plants in the power sector. SO2 emissions from combustion in energy industries have decreased by 99 per cent between 1990 and 2023, while emissions from industrial combustion have decreased by 93 per cent since 1990.

The decrease in SO2 emissions in recent years, with UK emissions having decreased by 77 per cent between 2012 and 2023, was largely due to the closure or the conversion to biomass-based fuels of many coal-fired power stations. This has significantly reduced the overall coal-burning capacity in the UK’s power stations.

SO2 emissions from domestic combustion are estimated to have fallen by 75 per cent from 1990 to 2023. In 2023, most emissions from this source came from the combustion of petroleum coke in fireplaces and stoves.

Levels and trends in emissions from specific sources are available for the period 1990 to 2023 through the statistical tables that accompany this release.

Sections in this release

Summary

Background

Emissions of particulate matter (PM10 and PM2.5)

Emissions of nitrogen oxides

Emissions of ammonia

Emissions of non-methane volatile organic compounds

Compliance with the Code of Practice for Statistics and Defra group Statistics quality principles, and recent changes to the publication

Methods and quality processes for UK air pollutant emissions statistics (PDF)

Statistical tables (ENV01 – Emissions of air pollutants)