Emissions of acidifying substances (version 1) (CSI 001) - Assessment published Mar 2008

Indicator definition

The indicator tracks trends since 1990 in anthropogenic emissions of acidifying substances: Nitrogen oxides, ammonia, and sulphur dioxide, each weighted by their acidifying potential.

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).

Units

ktonnes (acidifying equivalent)

Policy context and targets

Context description

Emission ceiling targets for NO_x, SO₂ and NH₃ are specified in both the EU National Emission Ceilings Directive (NECD) [4] and the Gothenburg protocol under the United Nations Convention on Long-Range Transboundary Air Pollution (LRTAP Convention) (UNECE 1999). Emission reduction targets for the new EU-12 Member States have been specified in a consolidated version of the NECD for the EU-25 [1] which was adopted by the European Community after the accession of the EU-10 Member States. In addition, the consolidated NECD also includes emission ceilings for Bulgaria and Romania whose targets have been defined in their respective Accession treaties [2].

1. http://ec.europa.eu/environment/air/pdf/necd_consolidated.pdf

2. http://ec.europa.eu/environment/air/pdf/eu27_nat_emission_ceilings_2010.pdf

3. UNECE (1999). Protocol to the 1979 Convention on Long-Range Transboundary air pollution (LRTAP Convention) to abate acidification, eutrophication and ground-level ozone, Gothenburg, Sweden, 1 December 1999.

4. Directive 2001/81/EC, on national emissions ceilings (NECD) for certain atmospheric pollutants.

Targets

Emissions of NO_x, SO_x and NMVOCs 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.

Table 1. Percentage reduction required by 2010 from 1990 levels by country, for emissions of ozone precursors NO_x and NMVOCs (emission targets weighted by ozone formation potential).

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.
• 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.

Methodology

Methodology for indicator calculation

Base data is available from http://webdab.emep.int/ and from the EEA dataservice (http://dataservice.eea.europa.eu/). Base data, reported in NFR are converted into the following EEA sector codes to obtain a common reporting format across all countries and pollutants:

-          Energy industry: Emissions from public heat and electricity generation

-          Fugitive emissions: Emissions from extraction and distribution of solid fossil fuels and geothermal energy

-          Industry (Energy): relates to emissions from combustion processes used in the manufacturing industry including boilers, gas turbines and stationary engines

-          Industry (Processes): Emissions from production processes

-          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;

-          Agriculture: manure management, fertiliser application, field-burning of agricultural wastes

-          Waste: incineration, waste-water management.

-          Other (energy-related) covers energy use principally in the services and household sectors

-          Other (Non Energy): Emissions from solvent and other product use.

The current Nomenclature for Reporting (NFR) reporting format used by countries includes 103 separate emission categories. The following table shows how these NFR categories are aggregated into EEA sector codes:

Where reported data from countries is incomplete, simple gap-filling techniques are used in order to obtain a consistent time-series (see following section). To obtain emission values for the acidifying substances, the gap-filled emission values are multiplied by an acidifying potential factor, (de Leeuw, 2002). The factors are NO_x 0.02174, SO₂ 0.03125 and NH₃ 0.05882. Results are expressed in acidification equivalents ktonnes. For the main indicator trend graph, emissions are shown indexed to 1990 values (1990 emission =100). The sectoral shares are the share of the specific sector relative to the sum of all sectors for a given year. 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 they are consistent with the sum of the individual sectors reported by countries.

Methodology for gap filling

To allow trend analysis, where countries have not reported data for one or more years, data has been interpolated to derive the emissions for the missing year or years. If the reported data is missing either at the beginning or at the end of the period, the emission value is assumed to equal the first or last reported value. The use of gap-filling may 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. A list of the gap-filled dataset, plus a spreadsheet containing a record of the gap-filled data is available from EEA's dataservice (http://eea.eionet.europa.eu/Members/irc/eionet-circle/etcacc/library).

Methodology references

• EEA/ETC-ACC technical report describing the gap-filling methodologies used for the 2004 EEA/ETC-ACC LRTAP Convention and GHG (CRF) air emissions spreadsheet
• de Leeuw , F. (2002). A set of emission indicators for long-range transboundary air pollution. Environmental Science and Policy, Volume 5, Issue 2, p. 135-145. Abstract For assessing the progress made to mitigate the environmental problems related to long-range transboundary air pollution, emission indicators are developed for total potential acid, secondary PM 10 and ground-level ozone. The indicators are based on a weighted summation of emission data of the relevant precursors (SO 2 , NO x , NH 3 and VOC). By using comparable and reliable emissions data provided by the EU member states, the indicators provide clear information on the contribution of economic sectors and on the gap between current emissions and the emission targets set for 2010.

Uncertainties

Methodology uncertainty

The use of acidifying potential factors leads to some uncertainty. The factors are assumed to be representative for Europe as a whole; on the local scale different factors might be estimated. An extensive discussion on the uncertainties in these factors is available in de Leeuw (2002).

Data sets uncertainty

EEA uses data officially submitted by EU Member States and other EEA member countries which follow common guidelines on the calculation and reporting of emissions (EMEP/EEA 2006) [1] for the air pollutants NO_x, SO₂ and NH₃.

Sulphur dioxide emission estimates in Europe are thought to have an uncertainty of about 10% as the sulphur emitted 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 here will have higher uncertainty. EMEP has compared modelled and measured concentrations throughout Europe [2]. From these studies differences in the annual averages have been estimated in the order of 30% consistent with an inventory uncertainty of 10% (there are also uncertainties in the measurements and especially the modelling).

Nitrogen oxide emission estimates in Europe are thought to have an uncertainty of about 30%, as the NO_x emitted comes both from the fuel burnt and the combustion air and so cannot be estimated accurately from fuel nitrogen alone.  EMEP has compared modelled and measured concentrations throughout Europe (EMEP 1998).  From these studies differences for individual monitoring stations of up to a factor of two have been found.  This is consistent with an inventory of national annual emissions having an uncertainty of 30% (there are also uncertainties in the measurements and especially the modelling).

Ammonia emissions are also relatively uncertain. Total uncertainty ranges in emission estimates have been estimated to be as much as 50% [3]. Emissions from the agricultural sector are also associated with considerable uncertainty. This is due to the complex interaction of many environmental and management factors that can lead to significant regional variations in emissions occurring and which may make the application of default emission factors imprecise.

[1] (EMEP/EEA 2006). EMEP/CORINAIR Emission Inventory Guidebook - 2006 (http://reports.eea.europa.eu/EMEPCORINAIR4/en/page002.html)

Rationale uncertainty

This indicator on emissions of acidifying pollutants 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.