Indicator Assessment

Nitrogen oxides (NOx) emissions

Indicator Assessment
Prod-ID: IND-166-en
  Also known as: APE 002
Published 29 Jan 2014 Last modified 11 May 2021
24 min read
This page was archived on 22 Feb 2018 with reason: No more updates will be done
    • EEA-33 emissions of nitrogen oxides (NOX) decreased by 44% between 1990 and 2011. In 2011, the most significant sources of NOX emissions were 'Road transport' (41%), 'Energy production and distribution' (23%) and the 'Commercial, institutional and households' (13%) sectors.
    • The largest reduction of emissions in absolute terms since 1990 has occurred in the road transport sector, from which emissions in the EEA-33 have fallen 48% since 1990; in all years since 1990, emissions in this sector have fallen compared with the previous year, by an average of 3% per year. This reduction has been achieved despite the general increase in activity within this sector since the early 1990s and has primarily been achieved as a result of fitting three-way catalysts to petrol fuelled vehicles. However, ambient urban concentrations of NO2 in EU-28 countries in recent years have not fallen by as much as reported emissions and a number of Member States' NOX emissions could therefore be systematically higher than currently calculated.
    • In the electricity/energy production sector, reductions have occurred as a result of measures such as the introduction of combustion modification technologies (e.g. the use of low NOX burners, which reduce formation of NOX in combustion), the implementation of flue-gas abatement techniques (e.g. NOX scrubbers and selective catalytic and non-catalytic reduction techniques - SCR and SNCR) and fuel-switching from coal to gas (which has significantly lower NOX emissions per unit energy).
    • The National Emission Ceilings Directive (NECD) specifies NOX emission ceilings for Member States that must have been met by 2010. In general, the newer EU Member States have made substantially better progress against their respective NOX ceilings than the older Member States of the EU-15. Twelve of the EU-13 Member States had reduced their emissions beyond what is required under the NECD[1] by 2010, and by 2011 all had met their targets. In contrast, only five EU-15 Member States reported 2010 emissions within their respective national ceilings and by 2011 this had increased to just eight. Of the three non-EU countries having emission ceilings set under the UNECE/CLRTAP Gothenburg protocol, only Switzerland reported 2011 emissions below the level of their 2010 ceiling.
    • Environmental context: NOX contributes to acid deposition and eutrophication of soil and water. 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. NO2 is associated with adverse effects on human health, as at high concentrations it can cause inflammation of the airways and reduced lung function, increasing susceptibility to respiratory infection. It also contributes to the formation of secondary particulate aerosols and tropospheric ozone in the atmosphere, both of which are important air pollutants due to their adverse impacts on human health and other climate effects.


[1] Emissions data reported by EU member states under NECD is used for comparison with NECD ceilings, while data reported under CLRTAP is used for all other calculations unless otherwise stated.

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

Change in emissions of nitrogen oxides compared with the 2010 NECD and Gothenburg protocol targets


Distance-to-target for nitrogen oxides


EEA-33 NOX emissions have decreased by 44% between 1990 and 2011. The majority of EEA-33 countries reported lower emissions of NOX in 2011 compared to 1990. The exceptions to this are Turkey (whose emissions were two times higher in 2011 than in 1990), Cyprus (24% higher), Luxembourg (24%) and Malta (4%).

The recession, and subsequent economic slow-down, that commenced mid-2008 was a key driver in the reduction of NOX emissions between 2007 and 2011, primarily due to reductions in the level of industrial and transport activities across Europe. Total emissions were reduced by 17% between these years, compared to a 7% reduction between 2003 and 2007.

In general, the newer Member States of the European Union have made better progress towards meeting their respective 2010 NOX ceilings than the older EU-15 Member States. All of the EU-13 Member States, which joined between 2004 and 2013, have reduced emissions beyond what is required under the NECD. In contrast, only eight EU-15 Member States had 2011 emissions below their respective national ceilings.

Despite this difference both EU-15 and New EU-13 groups have achieved broadly similar reductions in NOX emissions since 1990, of 49.1% and 48.7% respectively. However NECD ceilings for the groups are markedly different, representing reductions from 1990 emissions of 52% and 31% respectively. This difference is reflected less in the revised Gothenburg Protocol, under which the EU-15 and EU-13 groups are expected to achieve reductions of 44% and 35% respectively from 2005 levels of emissions.

As noted above, emissions have actually increased in four EEA-33 countries during the period 1990-2011, despite all countries having obligations to reduce emissions under the NECD and Gothenburg Protocol. Since 2005, however, emissions have fallen in all but one of these countries, indicating that by 2011 some progress had been made in moving towards their NECD ceiling directive limits.

Iceland, Liechtenstein, Norway, Switzerland and Turkey are not members of the European Union and hence have no emission ceilings set under the NECD. However, Norway and Switzerland have ratified the UNECE LRTAP Convention's Gothenburg Protocol, requiring them to reduce their emissions to the agreed ceiling specified in the protocol by 2010. Liechtenstein has also signed, but not ratified the protocol. While Switzerland has reported emissions in 2011 that were lower than their ceiling, neither Liechtenstein nor Norway has yet met their national ceilings, and thus must still make significant reductions if they are to ensure compliance.

The revision of the National Emission Ceilings Directive 2001/81/EC (NECD) is part of the implementation of the Thematic Strategy on Air Pollution. The proposal to amend the NECD is still under preparation and should set emission ceilings to be respected by 2020 for the four already regulated substances (NOX, NMVOC, SOX and NH3), as well as for the primary emissions of PM2.5. A revision of the Gothenburg protocol was published in June 2012 and proposed percentage emission reductions from 2005 levels to be met by 2020 for the four already regulated substances and primary emissions of PM2.5. Existing emission ceilings for 2010 have been extended to 2020 such that all countries have additional obligations to maintain emission levels below their 2010 ceilings, or to further reduce emissions if they have not yet met these ceilings.

Emissions reported for 2011 indicate that the majority of Member States are on track towards meeting their proposed 2020 emission reduction targets under the revised Gothenburg protocol. Eight countries reported 2011 emissions higher than the linear path to their 2020 targets, however, for five of these the difference was less than 10% of 2005 emissions.

Sector share of nitrogen oxides emissions


Change in nitrogen oxides emissions for each sector


Contribution to total change in nitrogen oxides emissions for each sector


Reductions of NOX emissions have occurred in all economic sectors during this period. The sectors responsible for the vast majority of the decline in NOX emissions are 'Road transport' (contributing 47% of the total reduction in NOX emissions reported by countries) and 'Energy production and distribution' (contributing 27%).

Significant reductions have occurred in the 'Road transport' sector since the early 1990s, with a 48% overall decline in reported emissions between 1990 and 2011. This has been achieved despite the general increase in transport activity within this sector over the period. The emission reductions have primarily been achieved as a result of fitting catalysts to vehicles (driven by the legislative 'Euro' standards). However, across Europe there is also an increasing awareness of the contribution made to NOX pollutant emissions by national and international ship traffic (a more detailed discussion of this issue is contained in the TERM indicator fact sheet TERM03 - Transport emissions of air pollutants).

Although the largest reduction of emissions in absolute terms since 1990 has occurred in the road transport sector, ambient urban concentrations of NO2 in EU-28 countries in recent years have not fallen by as much as reported emissions. From 2001 to 2010, NO2 annual mean concentrations at urban background sites fell by just 10.6% on average (CSI004 - Fig 5), during which time the reported NOX emissions for the EU-28 decreased by 29.5%. The disparity between trends in NOX emissions and ambient NO2 concentrations is due in part to increased penetration of diesel vehicles, and the ‘real-world’ emission performance of modern diesel vehicles not showing the improvements that were indicated by the test cycle emission factors used for emission inventories. The disparity is also due to the increased proportion of NOX emitted directly as NO2 from the exhausts of more modern diesel vehicles, which use catalyst systems for controlling emissions of other pollutants.

Emissions of NOX have also declined in the 'Energy production and distribution' sector (by 48% between 1990 and 2011). This has been achieved through the implementation of measures such as combustion modification, introduction of flue-gas abatement techniques and fuel-switching from coal to gas. One of the most common forms of combustion modification is to use low NOX burners, which typically can reduce NOX emissions by up to 40%. Flue gas treatment techniques (such as NOX scrubbers, selective catalytic or non-catalytic reduction techniques - SCR and SNCR) can also be used to remove NOX from the flue gases. Emissions of NOX are higher from coal-fired power plants than from gas-fired plants as the coal contains significant amounts of nitrogen (unlike gas) and is burnt in less efficient combustion processes.

The newer Member States of the European Union have, in a number of cases, also undergone significant economic structural changes since the early 1990s, which has led to a general decline in certain activities that previously contributed to high levels of NOX emissions e.g. heavy industry and the closure of older, less efficient, power plants, and replacement of old vehicles with newer vehicles that meet Euro standards.

Supporting information

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


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 (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 ecosystems from transboundary pollution by setting emission reduction ceilings to be reached by 2010 for the same four 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 pre-1987) by either complying with the ELVs or operating 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 and existing installations, which are subject to 'substantial changes', have been required to meet the requirements of the IPPC Directive since 30 October 1999. Other existing installations must have been brought into compliance by 30 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 21 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 1 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 standards 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. 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 NOX ceilings under the NEC Directive and the Gothenburg Protocol (kt)


2010 NECD

2010 CLRTAP Gothenburg Protocol ceilings

2020 CLRTAP Gothenburg Protocol ceilings

Austria 103 107 149
Belgium 176 181 172
Bulgaria 247 266 91
Cyprus 23 N/A 12
Czech Republic 286 286 181
Denmark 127 127 80
Estonia 60 N/A 30
Finland 170 170 110
France 810 860 715
Germany 1051 1081 963
Greece 344 344 289
Hungary 198 198 134
Iceland* N/A N/A N/A
Ireland 65 65 65
Italy 990 1000 727
Latvia 61 84 25
Liechtenstein N/A 0.37 N/A
Lithuania 110 110 29
Luxembourg 11 11 35
Malta 8 N/A 5
Netherlands 260 266 190
Norway N/A 156 154
Poland 879 879 606
Portugal 250 260 167
Romania 437 437 170
Slovakia 130 130 65
Slovenia 45 45 28
Spain 847 847 827
Switzerland N/A 79 55
Sweden 148 148 111
Turkey* N/A N/A N/A
United Kingdom 1167 1181 711

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

Related policy documents



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 ( and the EMEP web site ( 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 (

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:

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 (excl. 1A3b)


Industrial processes



Solvent and product use









Commercial, institutional and households

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





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 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.



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

NOX emissions estimates in Europe are thought to have an uncertainty of about ±20% (EMEP, 2010), as the NOX 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.

Data sources

Other info

DPSIR: Pressure
Typology: Performance indicator (Type B - Does it matter?)
Indicator codes
  • APE 002
Frequency of updates
This indicator is discontinued. No more assessments will be produced.
EEA Contact Info


Geographic coverage

Temporal coverage