Environment at a Glance 2013
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branch 1. Environmental trends
  branch Sulphur oxides (SOx) and nitrogen oxides (NOx) emissions

Atmospheric pollutants from energy transformation and energy consumption, but also from industrial processes, are the main contributors to regional and local air pollution. Major concerns relate to their effects on human health and ecosystems.

In the atmosphere, emissions of sulphur and nitrogen compounds are transformed into acidifying substances such as sulphuric and nitric acid. When these substances reach the ground, acidification of soil, water and buildings arises. Soil acidification is one important factor causing forest damage; acidification of the aquatic environment may severely impair the life of plant and animal species.

Nitrogen oxides (NOx) also contribute to ground-level ozone formation and are responsible for eutrophication, reduction in water quality and species richness. They are associated with adverse affects on human health as high concentrations cause respiratory illnesses.


The indicators presented here refer to total emissions from human activities of sulphur oxides (SOx) and nitrogen oxides (NOx), given as quantities of SO2 and NO2. They show changes in emissions over time, as well as emission intensities per unit of GDP and per capita.

It should be kept in mind that SOx and NOx emissions provide only a partial view of air pollution problems. They should be supplemented with information on the acidity of rain and snow in selected regions, and the excedance of critical loads in soil and water, which reflect the actual acidification of the environment.


Compared to 1990, SOx emissions have decreased significantly for the OECD as a whole as a combined result of structural changes in the economy, changes in energy demand through energy savings and fuel substitution, pollution control policies and technical progress.

SOx emission intensities per capita and per unit of GDP show significant variation among OECD countries. A strong decoupling of emissions from GDP is seen in many countries.

The Gothenburg Protocol, adopted in Europe and North America to reduce acid precipitation even further, has been in force since May 2005. Most countries reached the goal they fixed for 2010; some countries (mainly in Northern and Eastern Europe) reached the goal early.

NOx emissions have decreased in the OECD overall since 1990, but less than SOx emissions. Major progress in the early 1990s, particularly in OECD Europe, reflects changes in energy demand, pollution control policies and technical progress. However, these results have not compensated in all countries for steady growth in road traffic, fossil fuel use and other activities generating NOx.

Several countries attained the emission ceilings of the Gothenburg Protocol for 2010, but other countries had difficulties in doing so.

Emission intensities per capita and per unit of GDP show significant variations among OECD countries. Two-thirds of the countries have achieved a strong decoupling from economic growth since the 1990s; in a few countries emissions continue to grow in line with GDP.

Despite large reductions SOx and NOx emissions and subsequent improvements in air quality, acid deposition remains a concern, in particular in North America, and more needs to be done to assure the recovery of aquatic and terrestrial ecosystems.

See Annex A for decoupling trends and emission structure.



International data on SOx and NOx emissions are available for almost all OECD countries. The details of estimation methods for emissions such as emission factors and reliability, extent of sources and pollutants included in estimation, etc., may differ from one country to another.

The high emission levels of SOx for Iceland are due to SOx emissions from geothermal energy which represented 77% of total emissions in 2010.

OECD totals do not include Chile and Mexico.

For additional notes, see Annex B.


OECD Environment Statistics (database), http://dx.doi.org/10.1787/data-00598-en.

UNFCCC, “National Inventory Submissions 2012” , National Reports, http://unfccc.int/national_reports/annex_i_ghg_ inventories/national_inventories_submissions/items/6598.php.

European Monitoring and Evaluation Programme (EMEP) (2012), www.emep.int/.

Further information


UNECE (2012), “Convention on Long-Range Transboundary Air Pollution” , www.unece.org/env/lrtap/multi_h1.html.


Indicator in PDF Acrobat PDF page

1.3. Sulphur oxides (SOx) emissions and intensities
    Table in Excel
1.4. Nitrogen oxides (NOx) emissions and intensities
    Table in Excel

1.11. Change in SOx and NOx emissions, since 1990 Figure in Excel
Change in SO and NO emissions, since 1990
1.12. SOx and NOx emission intensities, 2010 Figure in Excel
 SO and NO emission intensities, 2010