Indicator Assessment

APE_F01: Emissions of acidifying substances - outlook from LRTAP

Indicator Assessment
Prod-ID: IND-50-en
  Also known as: Outlook 002
Published 08 Jun 2007 Last modified 11 May 2021
19 min read
This page was archived on 09 Feb 2021 with reason: Other (Discontinued indicator)

On the basis of existing policies and measures, emissions of almost all acidifying substances (NOx, NMVOC, SO2) of land-based air pollutants are expected to decline significantly (by 47% for NOx emissions, by 45% for NMVOCs, by 67% for SO2) up to 2030. In contrast, NH3 emissions will decline slightly (by 6%).

Hence, the EU as a whole is expected to comply with the 2010 targets of the national emission ceilings directive. However, while a number of Member States are well below their binding upper national emission ceilings, others are not on track.

The implementation of all feasible technical measures (best available technologies) is estimated to offer a considerable potential for further reductions in the emissions.

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Emissions of acidifying substances (Baseline and MTFR scenarios, index 100 in 2000)

Note: N/A

Data source:

EEA European Topic Centre on Air and Climate Change: International Institute for Applied Systems Analysis (IIASA) + Norwegian Meteorological Institute (, 2003-2004. Dataset: RAINS model.

The outlook assesses the European air emissions of acidifying substances expected over the 2000-2030 period for the baseline and the maximum technically feasible reductions scenarios (MTFR). It covers the following anthropogenic air pollutants: nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC), sulphur dioxide (SO2), and ammonia (NH3).

The following developments are expected:


For Nitrogen oxides (NOx) emissions

  • In the baseline scenario, emissions of NOx are expected to decrease by 47% in 2030 compared with 2000. Baseline emissions aggregated at the EU level are expected to comply with the compliance may vary between individual Member States.
  • Under the MTFR scenario, emissions are expected to be reduced in 2030 by half to 2.8 million tones.
  • The largest contributor to NOx emissions in 2000 was road transport (46%), followed by the power plant and other fuel conversions sector (26%). The non-road sector contributed 15% and manufacturing industry and production processes another 13%.
  • In the MTFR scenario, the importance of road transport emissions is reduced due to introduction of best available technology (38%); the power plant and other fuel conversions sector becomes responsible for 29% of the emissions, non-road transport for 17% and manufacturing industry and production processes for 16%.
  • International emissions from shipping are expected to increase considerably in the baseline scenario: in 2030 NOx emissions increase by 87% compared with 2000 and exceed land-based emissions of NOx.
  • The MTFR scenario indicates that the scope for reducing emissions through best available technology is very large for NOx (88%) for shipping.


For non-methane volatile compounds (NMVOC):

  • In the baseline scenario, emissions of NMVOCs are expected to decrease by 45% in 2030 (to 5.9 million tones).
  • In 2000, the largest contributor was road transport (45%), followed by the solvent use sector (28%). However, due to implementation of stringest controls on mobile sources, emissions from road transport are expected to be reduced by about 90%, representing about 12% in 2030, while the share of emissions from the solvent use and process sectors increase to 40% and 18% respectively.
  • Baseline emissions aggregated at the EU level are expected to comply with 2010 NECD ceilings, although compliance may vary between individual Member States.
  • Implementation of best available control technology in the MTFR scenario reduces the emissions by a further one third (to 4.1 million tones).
  • International emissions from shipping are expected to increase considerably in the baseline scenario: emissions of NMVOCs are projected to more than double.


For sulphur dioxide emissions (SO2):

  • In the baseline scenario, emissions of SO2 are expected to decrease by 67% (to 2.9 million tones). This is due to mainly to stringest controls in the energy sector, which will decrease its share from 65% to 32% in 2030.
  • Baseline emissions aggregated at the EU level are expected to comply with the 2010 NECD ceilings, although compliance may vary between individual Member States.
  • In the MTFR scenario emission are reduced by another 45% (to 1.1 million tones).
  • Under the MTFR scenario, the share of emissions from power plants is expected to decrease to 32%, with a simultaneous increase of the shares of manufacturing industries and production processes (to 25% and 29% respectively).
  • International emissions from shipping are expected to increase considerably in the baseline scenario: in 2030 SO2 emissions increase by 82% compared with 2000 and exceed land-based emissions of SO2.


For emissions of ammonia (CH3):

  • In contrast, NH3 emissions are projected to decrease only slightly (6%) to 3.6 million tones in 2030 in the baseline scenario.
  • Emissions from the EU-15 decrease while those from the New-10 increase slightly; however, the EU-15 still represents about 82% of EU emissions in 2030.
  • Baseline emissions aggregated at the EU level are expected to comply with the 2010 NECD emission ceilings by a thin margin.
  • The MTFR scenario indicates that the potential to reduce NH3 emissions is substantial and corresponds to a 40% reduction compared with baseline emissions.
  • In the MTFR scenario, the share of the agricultural sector in ammonia emissions remains at about 90% over the period, 82% of which originates from livestock farming. The remaining emissions stem mainly from the waste treatment sector.


The main reasons of the decreasing amount of NOx emissions of land-based air pollutants appeared from the implementations of the strict standards and controls required by the accessed EU emission sectoral legislations and with accordance to the main policy, which addressed air pollution issues in Europe, the National emission ceilings directive, and due to. There is no clear description of reason for shipping transport emissions.

*this assessment is based on the results of the RAINS model (a predecessor to the GAINS model) and published in the EEA Publication 'European Environmental Outlook 2005'.


Supporting information

Indicator definition


Emissions of acidifying pollutants tracks trends in anthropogenic emissions of acidifying substances such as nitrogen oxides, ammonia, and sulphur dioxide, each weighted by their acidifying potential. Outlook form EMEP LRTAP provides information for nitrogen oxides, sulphur dioxide and ammonia. It is presented in total volumes of pollutants from all sources by sectors: power plants, process industry, domestic, road transport, off-road, and other.

Model used:



UNECE Convention on Long-range Transboundary Air Pollution (LRTAP)

Temporal coverage:

Emissions' trends: 2000-2007, projections: 2010, 2020

Geographical coverage:

EU-27: Austria, Belgium, Bulgaria, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain, Sweden, United Kingdom, Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Romania, Slovakia, Slovenia; By country: Albania, Armenia, Austria, Azerbaijan, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, Ireland, Italy, Kazakhstan, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Republic of Moldova, Romania, Russian Federation, Serbia and Montenegro, Slovakia, Slovenia, Spain, Sweden, Switzerland, the former Yugoslav Republic of Macedonia, Turkey, Ukraine, United Kingdom.


The indicator is measured in Gg of acidifying pollutant per year (EMEP data base) and/or in kilotones per year /acidifying equivalent/ (GAINS/RAINS database)


Policy context and targets

Context description

Pan-European policy context

At the Pan-European level this indicators is related to the implementation of the 1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone. The Protocol sets emission ceilings for 2010 for four pollutants: sulphur, NOx, VOCs and ammonia. These ceilings were negotiated on the basis of scientific assessments of pollution effects and abatement options. Parties whose emissions have a more severe environmental or health impact and whose emissions are relatively cheap to reduce will have to make the biggest cuts.

EU policy context

Emission ceiling targets for NOx and SO2 are specified in both the EU National Emission Ceilings Directive (NECD) 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-10 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. 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] Directive 2001/81/EC, on national emissions ceilings (NECD) for certain atmospheric pollutants. (consolidated version)

[2] National emission ceilings for SO2, NOx, VOC and NH3, to be obtained by 2010.

EECCA policy context

Most of the EECCA countries ratified the 1979 Convention on Long-Range Transboundary Air Pollution. These are A list of countries ratified the 1979 Convention: Armenia (1997), Azerbajan (2002), Belarus (1980), Georgia (1999), Kazakhstan (2001), Kyrgyzstan (2000), Republic of Moldova (1995), Russian Federation (1980), the Ukraine (1980).

At the same time only two of them signed in the Gothenburg Protocol to abate acidification, eutrophication and ground-level ozone, notably Armenia (1999), Republic of Moldova (2000).


Pan-European level
Once the Gothenburg Protocol is fully implemented, European sulphur emissions should be cut by at least 63%, NOx emissions by 41% and its ammonia emissions by 17% compared to 1990.

The Protocol also sets tight limit values for specific emission sources (e.g. combustion plant, electricity production, dry cleaning, cars and lorries) and requires best available techniques to be used to keep emissions down. Guidance documents adopted together with the Protocol provide a wide range of abatement techniques and economic instruments for the reduction of emissions in the relevant sectors, including transport.

EU level

Emissions of NOx and SO2 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: Percentage reduction required by 2010 from 1990 levels by country, for emissions of acidifying substances: NOx, SOx and NH3 (emission targets weighted by acidifying potential).

Country group


NECD Targets 1990 - 2010

LRTAP Convention Gothenburg Protocol Targets 1990 - 2010


























































United Kingdom












Czech Republic



























































EECCA level
No specific targets at the sub-regional level are set.

Related policy documents



Methodology for indicator calculation


The projections of the acidifying pollutants for this outlook are based on the GAINS (former RAINS) Model. Its European implementation covers 43 countries in Europe including the European part of Russia. GAINS estimates emissions, mitigation potentials and costs for six air pollutants (SO2, NOx, PM, NH3, VOC) and for the six greenhouse gases included in the Kyoto protocol.

The new GAINS model incorporates the latest version of the RAINS-Europe model (Regional Air Pollution Information and Simulation) as it has been prepared and reviewed for the CAFE programme and the 2007 revision of the NEC directive. Emissions of pollutants are calculated as a product of activity level, uncontrolled emission factor, removal efficiency of control technology applied in a given sector, and implementation level of that technology in a given emission scenario.

Overview of the model

The Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS)-Model provides a consistent framework for the analysis of co-benefits reduction strategies from air pollution and greenhouse gas sources.

The model considers emissions of:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrogen oxides (NOx)
  • Nitrous oxide (N2O)
  • Particulate matter (TSP, PM10, PM2.5 and PM1)
  • Sulfur dioxide (SO2)
  • Volatile organic compounds (VOC)

Certain versions of the GAINS Model also contain:

  • Ammonia (NH3)
  • Carbon monoxide (CO)
  • Fluorinated greenhouse gases (F-Gases)

The GAINS Model consists of several screen options, which display information pertaining to:

  • Economic Activity Pathways
    activities causing emissions (energy production & consumption, passenger & freight transport, industrial and agricultural activities, solvent use, etc.)
  • Emission Control Strategies
    the evolution of emissions and control over a given time horizon
  • Emissions Scenarios
    emissions are computed for a selected emissions scenario (combination of energy pathway and emissions control strategy), emission factors, results displays, and input values are also available under this action
  • Emission Control Costs
    displays emission control costs computed for a selected emissions scenario
  • Impacts
    presents ecosystem sensitivities and human health impacts of air pollution
  • Data Management
    provides an interactive interface where owner-specific data can be modified, updated, exported, and downloaded

The GAINS Model simultaneously addresses health and ecosystem impacts of particulate pollution, acidification, eutrophication and tropospheric ozone. Simultaneously, the GAINS Model considers greenhouse gas emission rates and the associated value per ton of CO2 equivalence. Historic emissions of air pollutants and GHGs are estimated for each country based on information collected by available international emission inventories and on national information supplied by individual countries. The GAINS Model assesses emissions on a medium-term time horizon, emission projections are specified in five year intervals through the year 2030.

Options and costs for controlling emissions are represented by several emission reduction technologies. Atmospheric dispersion processes are often modeled exogenously and integrated into the GAINS Model framework. Critical load data and critical level data are often compiled exogenously and incorporated into the GAINS modeling framework.

The model can be operated in the 'scenario analysis' mode, i.e., following the pathways of the emissions from their sources to their impacts. In this case the model provides estimates of regional costs and environmental benefits of alternative emission control strategies. The Model can also operate in the 'optimization mode' which identifies cost-optimal allocations of emission reductions in order to achieve specified deposition levels, concentration targets, or GHG emissions ceilings. The current version of the model can be used for viewing activity levels and emission control strategies, as well as calculating emissions and control costs for those strategies.

 The The current version (June 2008) allows access to

  • the recent set of activity data and projections for all European countries that has been developed for the revision of the NEC directive,
  • computations of emissions, emission projections and control costs for the air pollutants (SO2, NOx, PM, NH3, VOC),
  • emissions, control measures and emission control costs of the optimized policy scenarios that are analyzed for the NEC review,
  • computation and display of concentration and deposition fields of selected air pollutants,
  • computation and display of health and environmental impacts of air pollutants,
  • emission inventories and projections for CO2,
  • estimates for the other greenhouse gases (CH4, N2O, HFC, PFC, SF6).
  • Atmospheric dispersion processes over Europe for all pollutants are modelled on the basis of results of the European EMEP model developed at the Norwegian Meteorological Institute (Simpson et al., 2003).Atmospheric dispersion processes over Europe for all pollutants are modelled on the basis of results of the European EMEP model developed at the Norwegian Meteorological Institute (Simpson et al., 2003).

For more information see: (requires regstration)

Overview of the EMEP model

The European Monitoring and Evaluation Program (EMEP) developed a Unified EMEP model in order to provide, on a regular basis, governments and other parties under the Convention on Long Range Transboundary Air Pollution with scientific information that can support the continuing development and evaluation of the protocols under the convention. Unified EMEP model combines several models. For integrated assessment analyses it uses RAINS model developed and maintained at the Center for Integrated Assessment Modeling (CIAM). It also uses MSC-W model for atmospheric dispersion and deposition of acidifying compounds, compounds causing eutrophication, ground level ozone and particulate matter developed by the Meteorological Synthesizing Centre West (MSC-W), one of the centers under the EMEP programme. Additionally it uses EMEP Chemical Transport Models for the regional atmospheric dispersion and deposition of heavy metals (Cd, Pb, Hg) and selected persistent organic compounds (PCB, PAH, HCB, PCDD/Fs, g-HCH). The latest model version has been documented in the EMEP Status report I, Part I (Simpson et. al., 2003) and the EMEP Status report 2004 (Tarrasón et al., 2004) where a few updates are described.

The model domain covers Europe and the Atlantic Ocean. The model grid has a horizontal resolution of 50 km at 60 0N, which is consistent with the resolution of emission data reported to CLRTAP. In the vertical, the model has 20 sigma layers reaching up to 100 hPa. The unified model uses 3-hourly resolution meteorological data from the PARLAM-PS model, a dedicated version of the HIRLAM (high resolution limited area model) numerical weather prediction model.

The emissions consist of girded annual national emissions of sulphur dioxide, nitrogen oxides, ammonia, non-methane volatile organic compounds and carbon monoxide. They are available in each cell of the 50 * 50 km2 model grid and distributed temporally according to monthly and daily factors derived from data provided by the University of Stuttgart (IER). Concentrations of 71 species are computed in the latest version of the Unified EMEP model (56 are advected and 15 are short-lived and not advected). Four secondary and two primary PM compounds are included in the model. The sulphur and nitrogen chemistry is coupled to the photo-chemistry, which allows a more sophisticated description of e.g. the oxidation of sulphur dioxide to sulphate, also including oxidant limitations.

Dry deposition is calculated using the resistance analogy and is a function of the pollutant type, meteorological conditions and surface properties. Parametrisation of wet deposition processes includes both in-cloud and sub-cloud scavenging of gases and particles using scavenging coefficients.

For more information see:

Use of Scenarios

The LRTAP uses GAINS/RAINS and EMEP to calculate global and European emissions for two categories of scenarios: 'current legislation'  and  'maximum technically feasible reduction' (MFR) scenarios.

The 'current legislation' (CLE) scenario reflects the current perspectives of individual countries on economic development and takes into account the anticipated effects of presently decided emission control legislation.

The 'maximum technically feasible reduction' (MFR) scenario outlines the scope for emission reduction offered by a full implementation of the best available emission control technologies. Considering this calculation as a theoretical analysis of the long-term reduction potential, practical limitations on the penetration of most advanced emission control measures imposed by the gradual turnover of existing capital stock especially in the short run are not taken in to account, and the obviously high costs of such a theoretical emission control strategy are not estimated. On the other hand, in this scenario the potential for emission reductions offered by structural changes, such as increased energy efficiency measures, fuel substitution, more efficient production technologies or reduced transport demand is not considered. Earlier studies have shown that the emission reduction potential of such measures is considerable and that some of them could be even cost-effective (e.g., Rentz et al., 1994, Van Vuuren et al., 2005). The latest version of the model allows to build scenarios which accounts for structural changes. Such set of scenarios is developed by the IISAA in order to identify new NEC for the EU.

Methodology for gap filling

The input data for RAINS model comes from different international sources as main data sets. National data were used for verification of the international data sources and for gap filling (see data sets).

For Unified EMEP model, officially reported country data constitutes maximum 60% of the data in the EMEP inventory; the remaining 40% are MSC-W estimates. For several countries, officially reported emissions were not available or not reliable for the years. They were analyzed in the framework of the model, and thus replaced with expert estimates. The largest source of MSC-W estimates is emission data from the regional European RAINS model.

Methodology references

No methodology references available.



Methodology uncertainty

RAINS model
A methodology has been developed to estimate uncertainties of emission calculations based on uncertainty estimates for the individual parameters of the calculation (Suutari et al., 2001). It was found that uncertainties in modeled national emissions of SO2 and NOx in Europe typically lie in the range between 10 and 30 percent (Outlook from RAINS model). In general, the uncertainties are strongly dependent on the potential for error compensation. This compensation potential is larger (and uncertainties are smaller) if calculated emissions are composed of a larger number of similar-sized source categories, where the errors in input parameters are not correlated with each other. Thus, estimates of national total emissions are generally more certain than estimates of sectoral emissions.

The uncertainty in input parameters showed that the actual uncertainties are critically influenced by the specific situation (pollutant, year, country). Generally, however, the emission factor is an important contributor to the uncertainty in estimates of historical emissions, while uncertainty in the activity data dominates the future estimates.

For more information see

EMEP models
Uncertainties in the model formulation itself give rise to uncertain deposition estimates. It has been shown that the EMEP model performance is rather homogeneous over the years (Fagerli et al. 2003b), but depend on geographical coverage and quality of the measurement data. The EMEP model has also been validated for nitrogen compounds in Simpson et al. (a) and for dry and wet deposition of sulphur, and wet depositions for nitrogen in Simpson et al. (b) with measurements outside the EMEP network.
For more information see

Data sets uncertainty

National projections reflect national governmental expectations and probably in many cases also merely policy ambitions. Thus there is no guarantee for international consistency, e.g., in the volumes of exports and imports or in the underlying assumptions on the development of oil prices. However, the value of this set of projections is that it reflects bottom-up expectations on economic development as seen today by the individual countries.

For more information see methodology uncertainty.

Rationale uncertainty


Data sources

Other info

DPSIR: Pressure
Typology: Performance indicator (Type B - Does it matter?)
Indicator codes
  • Outlook 002
EEA Contact Info


Geographic coverage


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