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Emissions of ozone precursors

Indicator Specification Created 19 Aug 2010 Published 25 Oct 2010 Last modified 04 Sep 2015, 06:59 PM
Indicator codes: CSI 002 , APE 008
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 non-methane volatile organic compounds (NMVOCs), nitrogen oxides, carbon monoxide and methane contribute to the formation of ground-level (tropospheric) ozone.

Ozone is a powerful oxidant and tropospheric ozone can have adverse effects on human health and ecosystems. It is a problem mainly during the summer months. High concentrations of ground-level ozone adversely affects the human respiratory system and there is evidence that long-term exposure accelerates the decline in lung function with age and may impair the development of lung function. Some people are more vulnerable to high concentrations than others, with the worst effects generally being seen in children, asthmatics and the elderly. High concentrations in the environment are harmful to crops and forests, decreasing yields, causing leaf damage and reducing disease resistance.

Detailed information on individual acidifying pollutant emissions may also be found in the accompanying indicator fact-sheets for nitrogen oxides and non-methane volatile organic compounds.

Scientific references

  • No rationale references available

Indicator definition

  • This indicator tracks trends since 1990 in anthropogenic emissions of ozone precursor pollutants: nitrogen oxides (NOX), carbon monoxide (CO), methane (CH4) and non methane volatile organic compounds (NMVOCs).
  • 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 NOX and NMVOCs (the NEC Directive also sets emissions ceilings for ammonia NH3 and sulphur dioxide SO2). There are no specific EU emission targets set for either carbon monoxide (CO) or methane (CH4). However, there are several Directives and Protocols that affect the emissions of CO and CH4. Methane is included in the basket of six greenhouse gases under the Kyoto protocol (see CSI 010: Greenhouse gas emissions and removals).

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 NOXand NMVOC 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 the period 1990-2010.

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

2010 NECD ceilings

2010 CLRTAP Gothenburg Protocol ceilings






Austria 103 159 107 159
Belgium 176 139 181 144
Bulgaria 247 175 266 185
Cyprus 23 14
Czech Republic 286 220 286 220
Denmark 127 85 127 85
Estonia 60 49
Finland 170 130 170 130
France 810 1050 860 1100
Germany 1051 995 1081 995
Greece 344 261 344 261
Hungary 198 137 198 137
Ireland 65 55 65 55
Italy 990 1159 1000 1159
Latvia 61 136 84 136
Liechtenstein 0.37 0.86
Lithuania 110 92 110 92
Luxembourg 11 9 11 9
Malta 8 12
Netherlands 260 185 266 191
Norway 156 195
Poland 879 800 879 800
Portugal 250 180 260 202
Romania 437 523 437 523
Slovakia 130 140 130 140
Slovenia 45 40 45 40
Spain 847 662 847 669
Switzerland 79 144
Sweden 148 241 148 241
United Kingdom 1167 1200 1181 1200


* 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.
  • Greenhouse gas monitoring mechanism
    Decision No 280/2004/EC of the European Parliament and of the Council of 11 February 2004 concerning a mechanism for monitoring Community greenhouse gas emissions and for implementing the Kyoto Protocol
  • 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 ozone precursors across Europe?

Specific policy question

How do different sectors and processes contribute to emissions of ozone precursors?


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/ACM 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

National totals without LUCF

Energy production and distribution

1A1, 1A3e, 1B


Energy use in industry



Road transport



Non-road transport (non-road mobile machinery)

1A3 (exl 1A3b)

1A3a, 1A3c, 1A3d, 1A3e

Industrial processes



Solvent and product use








Commercial, institutional and households

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

1A4, 1A5



3 + 7


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

NMVOC emission estimates in Europe are thought to have an uncertainty of about ±30% due in part to the difficulty in obtaining good emission estimates for some sectors and partly due to the absence of good activity data for some sources. 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


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

Uncertainties in emissions of CO are likely to have a similar magnitude of uncertainty as for NOX. NMVOC emissions data have been verified by EMEP and others by means of comparison between modelled and measured concentration throughout Europe. From these studies total uncertainty ranges have been estimated to about ±50%. Some main source categories are less uncertain.

CH4 estimates are reasonably reliable as they are based on a few well-known emission sources. The IPCC believes that the uncertainty in CH4 emission estimates from all sources, in Europe, is likely to be about ±20 %. CH4 emissions from some sources, such as rice fields, are much larger (possibly an order of magnitude), but are a minor emission source in Europe. In 2004, EU Member States reported uncertainties in their estimates of CH4 emissions from enteric fermentation as ranging between 0.5 % (UK) and 2.8 % (Ireland) of the total national GHG emissions (EEA 2004).

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 002
APE 008
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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