Nitrogen oxides (NOx) emissions

Assessment versions

Published (reviewed and quality assured)

• No published assessments

Rationale

Justification for indicator selection

Nitric oxide (NO) and nitrogen dioxide (NO₂) are together referred to as nitrogen oxides (NO_X). Combustion of fossil fuels is by far the dominant source of NO_X emissions. The emissions are not dependent solely on the amount of nitrogen in the fuel but also on the air-fuel mix ratio. High temperatures and oxidation-rich conditions generally favour NO_X formation in combustion.

NO_X contributes to acid deposition and eutrophication which, in turn, can lead to potential changes occurring in soil and water quality. The subsequent impacts of acid deposition can be significant, including adverse effects on aquatic ecosystems in rivers and lakes and damage to forests, crops and other vegetation. Eutrophication can lead to severe reductions in water quality with subsequent impacts including decreased biodiversity, changes in species composition and dominance, and toxicity effects. In many cases, the deposition of acidifying and eutrophying substances still exceeds the critical loads of the ecosystems (see EEA indicator Core Set Indicator (CSI) 005 'Exposure of ecosystems to acidification, eutrophication and ozone'). Further details concerning emissions of acidifying pollutants are provided in EEA CSI 001 'Emissions of acidifying substances.

It is NO₂ that is associated with adverse affects on human health, as at high concentrations it can cause inflammation of the airways. NO₂ also contributes to the formation of secondary particulate aerosols and tropospheric ozone (O₃) in the atmosphere - both are important air pollutants due to their adverse impacts on human health. NO_x is therefore linked both directly and indirectly to effects on human health. Further details concerning the contribution of NO_X to emissions of tropospheric ozone precursors and particulate matter are contained in EEA CSI 002 'Emissions of ozone precursors' and CSI 003 'Emissions of primary particles and secondary particulate precursors'.

Scientific references

• No rationale references available

Indicator definition

• This indicator tracks trends since 1990 in anthropogenic emissions of nitrogen oxides.
• 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

Units

kilotonnes (1000 tonnes)

Policy context and targets

Context description

• A number of policies have been implemented that directly or indirectly reduce the emissions of nitrogen oxides. These include: The National Emission Ceilings Directive 2001/81/EC (NECD), which entered into force in the European Community in 2001. The NECD sets emission ceilings for four important air pollutants (NO_x, sulphur dioxide (SO₂), ammonia (NH₃) and non-methane volatile organic compounds (NMVOCs)) to be achieved from 2010 onwards for each Member State. The ceilings are designed to improve the protection in the Community of the environment and human health against risks of adverse effects arising from acidification, eutrophication and ground level ozone. The NECD is presently under review, the European Commission may adopt a proposal for a revised Directive during 2010.

• In parallel with vehicle technology developments, improvements in the quality of petrol and diesel fuels have been made as a result of the EU Directive on fuel quality (98/70/EC as amended by 2003/17/EC). Fuel quality has little effect on NO_x emissions directly, but improvements in fuel quality have allowed the fitting of exhaust after-treatment technologies and provided better catalyst performance, hence helping to reduce NO_x emissions further. 

• Directive 97/68/EC on the emissions of pollutants from internal combustion engines installed in non-road mobile machinery sets emission standards and type approval procedures for engines fitted to non-road mobile machinery.

Targets

Emissions of NO_X 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 countries for the period 1990-2010. The Gothenburg Protocol entered into force on 17 May 2005, after ratification by 16 countries early in 2005. The 2012 revision to the Gothenburg protocol proposed emission reduction targets for 2020 relative to 2005 reported emissions for all EU-27 Member States and some EEA-32 non-EU member states.

Table: 2010 NO_X ceilings under the NEC Directive and the Gothenburg Protocol (kt)

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

Related policy documents

• 1999 Protocol to Abate Acidification, Eutrophication and Ground-level Ozone
  Convention on Long-range Transboundary Air Pollution 1999 Protocol to Abate Acidification, Eutrophication and Ground-level Ozone, amended on 4 May 2012.
• Council Directive 96/61/EC (IPPC)
  Council Directive 96/61/EC of 24 September 1996 concerning Integrated Pollution Prevention and Control (IPPC). Official Journal L 257.
• Council Directive 96/62/EC of 27 September 1996
  Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management.
• Directive 97/68/EC of 16 December 1997
  Directive 97/68/EC of the European Parliament and of the Council of 16 December 1997 on the approximation of the laws of the Member States relating to measures against the emission of gaseous and particulate pollutants from internal combustion engines to be installed in non-road mobile machinery
• Directive 98/70/EC, quality of petrol and diesel fuels
  Directive 98/70/EC of the European Parliament and of the Council of 13 October 1998 relating to the quality of petrol and diesel fuels and amending Directive 93/12/EEC
• Directive 2001/80/EC, large combustion plants
  Directive 2001/80/EC of the European Parliament and of the Council of 23 October 2001 on the limitation of emissions of certain pollutants into the air from large combustion plants
• 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.
• DIRECTIVE 2003/17/EC
  It amends the Directive 98/70/EC relating to the quality of petrol and diesel fuels
• UNECE Convention on Long-range Transboundary Air Pollution
  UNECE Convention on Long-range Transboundary Air Pollution.

Methodology

Methodology for indicator calculation

This indicator is based on officially reported national total and sectoral emissions to the EEA and the 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 (http://dataservice.eea.europa.eu/dataservice/metadetails.asp?id=1096) and the EMEP web site (http://www.ceip.at/). Where necessary, gaps in reported data are filled by European Topic Centre/EEA using simple interpolation techniques (see below). The final gap-filled data used in this indicator are available from the EEA Data Service (http://dataservice.eea.europa.eu/PivotApp/pivot.aspx?pivotid=478)

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 metals;
• 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 and 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:

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 NO_X, SO_X, 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 is not yet complete and is 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

No methodology references available.

Data specifications

EEA data references

• National emissions reported to the Convention on Long-range Transboundary Air Pollution (LRTAP Convention) provided by United Nations Economic Commission for Europe (UNECE)
• National Emission Ceilings (NEC) Directive Inventory provided by Directorate-General for Environment (DG ENV)

Data sources in latest figures

Uncertainties

Methodology uncertainty

The use of gap-filling 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

NO_X emissions estimates in Europe are thought to have an uncertainty of about ±20% (EMEP, 2010), as the NO_X emitted comes from both 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

Rationale uncertainty

This indicator is regularly updated by the EEA and is used in state of the environment assessments. The uncertainties related to methodology and datasets are therefore of importance. Any uncertainties involved in the calculation and in the datasets need to be accurately communicated in the assessment to prevent erroneous messages influencing policy actions or processes.