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EEA-32 Nitrogen oxides (NOx) emissions

Indicator Specification Created 15 Oct 2009 Published 15 Feb 2010 Last modified 04 Sep 2015, 06:59 PM
Note: new version is available!
Indicator codes: APE 002

Assessment versions

Published (reviewed and quality assured)
  • No published assessments


Justification for indicator selection

Nitric oxide (NO) and nitrogen dioxide (NO2) are together referred to as nitrogen oxides (NOx). Combustion of fossil fuels is by far the dominant source of NOx 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 NOx formation in combustion.

NOx 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 CSI 005 'Exposure of ecosystems to acidification, eutrophication and ozone'). Further details concerning emissions of acidifying pollutants are provided in EEA's Core Set Indicator 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. NOx is therefore linked both directly and indirectly to effects on human health. Further details concerning the contribution of NOx to emissions of tropospheric ozone precursors and particulate matter are contained in EEA's Core Set Indicators 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

  • The indicator tracks trends since 1990 in anthropogenic emissions of nitrogen oxides.
  • The indicator also provides information on emissions by sectors: Energy industries; road and other transport; industry (processes and energy); other (energy); fugitive emissions; waste; agriculture and other (non energy).
  • 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: 1990-2007


ktonnes (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 (NOx, 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.
  • The Gothenburg Protocol (1999) to the United Nations Economic Commission for Europe's (UNECE) Convention on Long-Range Transboundary Air Pollution (LRTAP Convention) to abate acidification, eutrophication and ground-level ozone. 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.
  • The Large Combustion Plant Directive (2001/80/EC) is important in reducing emissions of NOx, SO2 and dust from combustion plants having a thermal capacity equal to or greater than 50 MW. Installations within the scope of this Directive include power stations, petroleum refineries, steelworks and other industrial processes running on solid, liquid and gaseous fuels. "New" plant must meet the emission limit values (ELVs) given in the LCPD. However Member States can choose to meet obligations for existing plant (i.e. those in operation per-1987) by either complying with the ELVs or they can operate within a national emission reduction plan (NERP) that sets a ceiling for each pollutant. The interaction of the LCPD and the IPPC Directive (see below) is currently being examined as part of a review of the IPPC Directive.   
  • The Directive on Integrated Pollution Prevention and Control (96/61/EC) entered into force in 1999. It aims to prevent or minimise pollution to air, water or land from various industrial sources throughout the European Union. Those installations covered by Annex I of the IPPC Directive are required to obtain authorisation from the authorities to operate. New installations and existing installations, which are subject to 'substantial changes' have been required to meet the requirements of the IPPC Directive since 30th October 1999. Other existing installations must have been brought into compliance by the 30th October 2007. The emission limit values outlined in the permit conditions must be based on the best available techniques (BAT). The Commission has been undertaking a review of the IPPC Directive and related legislation on industrial emissions and on the 21st December 2007 adopted a proposal for a Directive on industrial emissions. The proposal recasts seven existing Directives relating to industrial emissions (including IPCC and the LCPD) into a single legislative instrument.
  • The aim of the Directive 96/62/EC on ambient air quality assessment and management (the 'Air Quality Framework Directive') is to maintain and improve air quality within the European Community by establishing objectives for ambient air, drawing up common methods and criteria for assessing air quality and obtaining and disseminating information. The first "Daughter" Directive 99/30/EC entered into force in 1999 and set limit values for hourly and annual average nitrogen dioxide concentrations to be achieved throughout the community by 1st January 2010.
  • Since the early 1990s standards on NOx emissions from new cars sold in Europe have been in place. This first came about with EU Directive 91/441/EC, which effectively mandated the fitting of three-way catalysts to all new petrol cars to significantly reduce emissions of CO, hydrocarbons and NOx. Standards for this Directive, frequently referred to as Euro 1, were followed by Euro 2 standards implemented by Directive 94/12/EC during the mid 1990s. Yet more stringent EU Directives have been put in place to reduce NOx emissions further, the most recent being (98/69/EC) setting emission limits for petrol cars sold after 2000 and then after 2005 (Euro 3 and 4 standards respectively).
  • NOx emissions from diesel vehicles have also been regulated since the early 1990s (since 1988 for heavy duty vehicles) with a succession of more stringent EU Directives. The legislation currently in force for heavy duty vehicles is 2005/55/EC and 2005/78/EC (implementing provisions) which define the emission standard currently in force, Euro IV, as well as the next stage (Euro V) which entered into force in October 2008.
  • 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 NOx 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 NOx 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.


Emissions of NOx 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.


Table: Percentage reduction (#) required by 2010 from 1990 levels by country, for emissions of NOx


1990 - 2010: NECD
ceilings (%)

1990 - 2010: CLRTAP Gothenburg Protocol ceilings (%)













Czech Republic
























Iceland *

























































United Kingdom




# The actual 2010 emission ceilings specified in the NECD and Gothenburg Protocol are expressed as absolute emissions of SO2, NOx, NH3 and NMVOC (in ktonnes). For the purposes of this indicator 1990 is considered as a 'base year' and the percentage change to emissions to meet the ceilings is calculated. Reported emissions for past years may change reflecting e.g. updated and revised emission inventory guidance, and so the % reduction required to meet the CLRTAP and NECD targets as shown here may change slightly in the future. 

* Emissions data not available for Iceland.

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.
  • 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.

Key policy question

What progress is being made in reducing emissions of NOx?

Specific policy question

How do different sectors and processes contribute to emissions of NOx?


Methodology for indicator calculation

Indicator is based on officially reported national total and sectoral emissions to 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 2009. Recommended methodologies for emission inventory estimation are compiled in the EMEP/CORINAIR Atmospheric Emission Inventory guidebook, EEA Copenhagen (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 is available from the EEA Data Service (

Base data, reported in SNAP, draft NFR or NFR are aggregated into the following EEA sector codes to obtain a common reporting format across all countries and pollutants:

  • 'Energy industries': emissions from public heat and electricity generation, oil refining and production of solid fuels;
  • 'Fugitive emissions': Emissions from extraction and distribution of solid fossil fuels and geothermal energy;
  • 'Industry (Energy)': emissions from combustion processes used in the manufacturing industry including boilers, gas turbines and stationary engines;
  • 'Industry (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;
  • 'Off-road transport': railways, domestic shipping, certain aircraft movements, and non-road mobile machinery used in agriculture & forestry;
  • 'Other (energy-related)': emissions principally occurring from fuel combustion in the services and household sectors;
  • 'Other (Non Energy)': 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;
  • 'Unallocated': The difference between the reported national total and the sum of the sectors reported by a country.

The 'unallocated' sector corresponds to the difference between the reported national total and the sum of the reported sectors for a given pollutant / country / year combination. It can be either negative or positive. Inclusion of this additional sector means that the officially reported national totals do not require adjustment to ensure that they are consistent with the sum of the individual sectors reported by countries.

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)


0 National totals

National total

National totals without LUCF

1 Energy Industries



3 Industry (energy)



2 Fugitive emissions



7 Road transport



8 Other transport (non-road mobile machinery)

1A3 (exl 1A3b)

1A3a, 1A3c, 1A3d, 1A3e

9 Industry processes



4 Agriculture

4 + 5B


5 Waste



6 Other (energy)

1A4a, 1A4b, 1A4b(i), 1A4c(i), 1A5a

1A4, 1A5

10 Other (non-energy)

3 + 7

3 + 7

12 Energy industries (power production)



14 Unallocated

Difference between national total and sum of sectors (1 - 10)

Methodology for gap filling

EEA/ETC-ACC gap-filling methodology. To allow trend analysis where countries have not reported data for one or several years, data has been interpolated to derive annual emissions. If the reported data is missing either at the beginning or at the end of the time series period, the emission value has been considered to equal the first (or last) reported emission value. It is recognised that the use of gap-filling 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.

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, 2009), 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


Rationale uncertainty

This indicator on emissions of Nitrogen oxide is produced annually by EEA and is used regularly in its State of the Environment reporting. The uncertainties related to methodology and data sets are therefore of importance. Any uncertainties involved in the calculation and in the data sets need to be accurately communicated in the assessment, to prevent erroneous messages influencing policy actions or processes.

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


No owners.


Indicator code
APE 002
Version id: 1
Primary theme: Air pollution Air pollution


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

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