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Emissions of acidifying substances

Indicator Specification Created 19 Aug 2010 Published 25 Oct 2010 Last modified 04 Sep 2015, 06:59 PM
Indicator codes: CSI 001 , APE 007
This indicator is discontinued. No more assessments will be produced.

Assessment versions

Published (reviewed and quality assured)
  • No published assessments


Justification for indicator selection

Emissions of acidifying substances cause damage to human health, ecosystems, buildings and materials (corrosion). The effects associated with each pollutant depend on its potential to acidify and the properties of the ecosystems and materials. Substantial reductions in sensitive ecosystem areas subjected to deposition of excess acidity have occurred since 1990 and even more since 1980. Nevertheless, the area subjected to acid deposition beyond its critical loads in 2010 will still exceed about 10% of the EEA-32 natural ecosystem area.

The indicator supports assessment of progress towards meeting the national emission ceilings of the Gothenburg Protocol under the 1979 Convention on Long-range Transboundary Air Pollution (LRTAP Convention) and the EU Directive on National Emission Ceilings (NECD) (2001/81/EC).

Detailed information on individual acidifying pollutant emissions may also be found in the accompanying indicator fact-sheets for sulphur dioxide, nitrogen oxides and ammonia.

Scientific references

  • No rationale references available

Indicator definition

  • The indicator tracks trends since 1990 in anthropogenic emissions of the acidifying pollutants nitrogen oxides (NOX) , ammonia (NH3), and sulphur oxides (SOX as SO2).
  • The indicator also provides information on emissions by sectors: Energy production and distribution; Energy use in industry;, Industrial processes; Road transport; Non-road transport; Commercial, institutional and households; Solvent and product use; Agriculture; Waste; Other.
  • Geographical coverage: EEA-32. The EEA-32 country grouping includes countries of the EU-27 (Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, and the United Kingdom) EFTA-4 (Iceland, Liechtenstein, Switzerland and Norway) and Turkey.
  • Temporal coverage: 1990-2010.


ktonnes (1000 tonnes)

Policy context and targets

Context description

Within the European Union, the National Emission Ceilings Directive (NEC Directive) imposes emission ceilings (or limits) for emissions of the acidifying pollutants nitrogen oxides, sulphur dioxide and ammonia that harm human health and the environment (the NEC Directive also sets emissions ceilings for a fourth pollutant - non-methane volatile organic compounds).

Other key EU legislation is targeted at reducing emissions of air pollutants from specific sources, for example:

  • transport;
  • industrial facilities and other stationary sources.

Internationally, the issue of air pollution emissions is also being addressed by the UNECE Convention on Long-range Transboundary Air Pollution (the LRTAP Convention) and its protocols. A key objective of the protocol is to regulate emissions on a regional basis within Europe and to protect eco-systems from transboundary pollution by setting emission reduction ceilings to be reached by 2010 for the same 4 pollutants as addressed in the NECD (i.e. SO2, NOX, NH3 and NMVOCs). Overall for the EU Member States, the ceilings set within the Gothenburg protocol are generally either slightly less strict or the same as the emission ceilings specified in the NECD.


Emissions of SO2, NOX and NH3 are covered by the EU National Emission Ceilings Directive (NECD) (2001/81/EC) and the Gothenburg protocol under the United Nations Convention on Long-Range Transboundary Air Pollution (LRTAP Convention) (UNECE 1999). The NECD generally involves slightly stricter emission reduction targets than the Gothenburg Protocol for EU-15 Member States for 2010.

Table: 2010 Targets under the NEC Directive and the Gothenburg Protocol, in kt

2010 NECD ceilings

2010 CLRTAP Gothenburg Protocol ceilings








Austria 103 39 66 107 39 66
Belgium 176 99 74 181 106 74
Bulgaria 247 836 108 266 856 108
Cyprus 23 39 9
Czech Republic 286 265 80 286 283 101
Denmark 127 55 69 127 55 69
Estonia 60 100 29
Finland 170 110 31 170 116 31
France 810 375 780 860 400 780
Germany 1051 520 550 1081 550 550
Greece 344 523 73 344 546 73
Hungary 198 500 90 198 550 90
Ireland 65 42 116 65 42 116
Italy 990 475 419 1000 500 419
Latvia 61 101 44 84 107 44
Liechtenstein 0.37 0.11 0.15
Lithuania 110 145 84 110 145 84
Luxembourg 11 4 7 11 4 7
Malta 8 9 3
Netherlands 260 50 128 266 50 128
Norway 156 22 23
Poland 879 1397 468 879 1397 468
Portugal 250 160 90 260 170 108
Romania 437 918 210 437 918 210
Slovakia 130 110 39 130 110 39
Slovenia 45 27 20 45 27 20
Spain 847 746 353 847 774 353
Switzerland 79 26 63
Sweden 148 67 57 148 67 57
United Kingdom 1167 585 297 1181 625 297


* Iceland and Turkey do not have a ceiling under either the NEC Directive or the Gothenburg protocol.

Related policy documents

  • Directive 2001/81/EC, national emission ceilings
    Directive 2001/81/EC, on nation al emissions ceilings (NECD) for certain atmospheric pollutants. Emission reduction targets for the new EU10 Member States have been specified in the Treaty of Accession to the European Union 2003  [The Treaty of Accession 2003 of the Czech Republic, Estonia, Cyprus, Latvia, Lithuania, Hungary, Malta, Poland, Slovenia and Slovakia. AA2003/ACT/Annex II/en 2072] in order that they can comply with the NECD.
  • UNECE Convention on Long-range Transboundary Air Pollution
    UNECE Convention on Long-range Transboundary Air Pollution.

Key policy question

What progress is being made in reducing emissions of acidifying pollutants across Europe?

Specific policy question

How do different sectors and processes contribute to emissions of acidifying pollutants?


Methodology for indicator calculation

This indicator is based on officially reported national total and sectoral emissions to EEA and UNECE/EMEP (United Nations Economic Commission for Europe/Co-operative programme for monitoring and evaluation of the long-range transmission of air pollutants in Europe) Convention on Long-range Transboundary Air Pollution (LRTAP Convention), submission 2011. For the EU-27 Member States, the data used is consistent with the emissions data reported by the EU in its annual submission to the LRTAP Convention.

Recommended methodologies for emission inventory estimation are compiled in the EMEP/EEA Air Pollutant Emission Inventory Guidebook, (EMEP/EEA, 2009). Base data are available from the EEA Data Service ( and the EMEP web site ( Where necessary, gaps in reported data are filled by ETC/ACC using simple interpolation techniques (see below). The final gap-filled data used in this indicator are available from the EEA Data Service (

Base data, reported in the UNECE/EMEP Nomenclature for Reporting (NFR) sector format are aggregated into the following EEA sector codes to obtain a consistent reporting format across all countries and pollutants:

  • Energy production and distribution: emissions from public heat and electricity generation, oil refining,  production of solid fuels, extraction and distribution of solid fossil fuels and geothermal energy;
  • Energy use in industry: emissions from combustion processes used in the manufacturing industry including boilers, gas turbines and stationary engines;
  • Industrial processes: emissions derived from non-combustion related processes such as the production of minerals, chemicals and metal production;
  • Road transport: light and heavy duty vehicles, passenger cars and motorcycles;
  • Non-road transport: railways, domestic shipping, certain aircraft movements, and non-road mobile machinery used in agriculture & forestry;
  • Commercial, institutional and households: emissions principally occurring from fuel combustion in the services and household sectors;
  • Solvent and product use: non-combustion related emissions mainly in the services and households sectors including activities such as paint application, dry-cleaning and other use of solvents;
  • Agriculture: manure management, fertiliser application, field-burning of agricultural wastes
  • Waste: incineration, waste-water management;
  • Other: emissions included in national total for entire territory not allocated to any other sector


The following table shows the conversion of Nomenclature for Reporting (NFR) sector codes used for reporting by countries into EEA sector codes:

EEA classification

Non-GHGs (NFR)


National totals

National total


Energy production and distribution

1A1, 1A3e, 1B


Energy use in industry



Road transport



Non-road transport (non-road mobile machinery)

1A3 (exl 1A3b)


Industrial processes



Solvent and product use








Commercial, institutional and households

1A4ai, 1A4aii, 1A4bi, 1A4bii, 1A4ci, 1A4cii, 1A5a, 1A5b




In addition to historic emissions, Figure 1 of the indicator factsheet also shows the latest 2010 projection estimates reported by the EU-27 Member States under the NEC Directive. The "with measures" (WM) projections reported by Member States take into account currently implemented and adopted policies and measures. Where countries have instead reported "business as usual" or "current legislation" projections, it is assumed for comparison purposes that these are equivalent to a WM projection. The "with additional measures" projections reported by Member States take into account additional future planned policies and measures but which are not yet implemented.

Methodology for gap filling

An improved gap-filling methodology was implemented in 2010 that enables a complete time series trend for the main air pollutants (eg NOX, SOX, NMVOC, NH3 and CO) to be compiled. In cases where countries did not report emissions for any year, it meant that gap-filling could not be applied. For these pollutants, therefore, the aggregated data are not yet complete and are likely to underestimate true emissions. Further methodological details of the gap-filling procedure are provided in section 1.4.2 Data gaps and gap-filling of the European Union emission inventory report 1990–2009 under the UNECE Convention on Long-range Transboundary Air Pollution (LRTAP).

Methodology references

Data specifications

EEA data references

Data sources in latest figures


Methodology uncertainty

The use of gap-filling for when countries have not reported emissions for one of more years can potentially lead to artificial trends, but it is considered unavoidable if a comprehensive and comparable set of emissions data for European countries is required for policy analysis purposes.

Data sets uncertainty

NOX emission estimates in Europe are thought to have an uncertainty of about ±20% (EMEP, 2010), as the NOX emitted comes both from the fuel burnt and the combustion air and so cannot be estimated accurately from fuel nitrogen alone. However, because of the need for interpolation to account for missing data, the complete dataset used will have higher uncertainty. The trend is likely to be more accurate than the individual absolute annual values - the annual values are not independent of each other.

Overall scoring: (1-3, 1=no major problems, 3=major reservations)

  • Relevancy: 1
  • Accuracy: 2
  • Comparability over time: 2
  • Comparability over space: 2


SOX emission estimates in Europe are thought to have an uncertainty of about +/-10% as the sulphur comes from the fuel burnt and therefore can be accurately estimated. However, because of the need for interpolation to account for missing data, the complete dataset used will have higher uncertainty. EMEP has compared modelled and measured concentrations throughout Europe (EMEP 2010). From these studies, differences in the annual averages have been estimated to be +/-30%, which is consistent with an inventory uncertainty of +/-10% (there are also uncertainties in the measurements and especially the modelling). The trend is likely to be much more accurate than individual absolute values

Overall scoring: (1-3, 1=no major problems, 3=major reservations)

  • Relevancy: 1
  • Accuracy: 2
  • Comparability over time: 2
  • Comparability over space: 2


NH3 emission estimates in Europe are more uncertain than those for NOX, SOX and NMVOCs due largely to the diverse nature of major agricultural sources. It is estimated that they are around +/- 30% (EMEP, 2009). The trend is likely to be more accurate than the individual absolute annual values - the annual values are not independent of each other. 

Overall scoring: (1-3, 1=no major problems, 3=major reservations)

  • Relevancy: 1
  • Accuracy: 2
  • Comparability over time: 2
  • Comparability over space: 2

Rationale uncertainty

This indicator is regularly updated by EEA and is used in state of the environment assessments. The uncertainties related to methodology and data sets are therefore of importance.

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Martin Adams


European Environment Agency (EEA)


Indicator code
CSI 001
APE 007
Version id: 3
Primary theme: Air pollution Air pollution


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Frequency of updates

This indicator is discontinued. No more assessments will be produced.


DPSIR: Pressure
Typology: Performance indicator (Type B - Does it matter?)
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