Emissions of acidifying and eutrophying substances

The "Emissions of acidifying and eutrophying substances" fact sheet shows the emissions of sulphur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3), substances which contribute to acidification of the environment.

The emission of sulphur and nitrogen compounds into the atmosphere contributes to the reduction of soil and water pH levels. The consequences of acidification include the release of toxic metals, such as aluminium, and the leaching of nutrients in the soil, causing damage to flora and to fauna.

In addition, the atmospheric deposition of nitrogen compounds can contribute to an excess of nitrogenous nutrients in terrestrial and aquatic ecosystems, increasing nitrate concentrations in groundwater and altering biodiversity. The alteration of biodiversity results from the enrichment of the medium with nutrients that cause the overgrowth of some species over others which are used to a less nutrient-rich environment.

The indicator for acidifying and eutrophying substances aggregates in a single indicator the acidifying potential of pollutants such as sulphur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3).

In contact with air humidity, SO2 and NOx react producing sulphuric acid and nitrous acid, which transported by precipitation cause “acid rain”. Emissions of the three pollutants used for calculating the indicator are converted into tonnes of acid equivalent. This aggregation allows assessing the development of this type of emissions in the environment, as well as identifying the sectors that contribute significantly to acidification of the environment.

Maximum national ceilings for annual emission of acidifying and eutrophying substances were established by the Gothenburg Protocol and the Ceilings Directive for pollutants such as sulphur dioxide (SO2), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOC) and ammonia (NH3). These national ceilings values for acidifying and eutrophying substances establish the obligation to reduce emissions in order to reach, as of 2010, the assigned national emission ceilings.

In 2018, the Decree-Law No. 84/2018, which transposes the National Emissions Ceilings Directive (NECD) (Directive 2016/2284), was approved. It establishes commitments to reduce atmospheric emissions for 2020 and 2030 compared to the base year of 2005. In 2020 the new reduction commitments compared to 2005 are: -63% for SO2, -36% for NOx and -7% for NH3. By 2030 the reduction targets compared to 2005 are: -83%, -63% and -15% for pollutants SO2, NOx and NH3 respectively.

This fact sheet concerns mainland Portugal and shall be updated on an annual basis.

Objectives and targets: 
  • The Convention on Long-range Transboundary Air Pollution (CLRTAP) of the United Nations Economic Commission for Europe set as targets for air emissions in 2010: SO2=170 kt; NO2=260 kt; and NH3=108 kt (Decree No. 20/2004). The amendments to the Gothenburg Protocol approved by the CLRTAP Decision 2012/2 set emission reduction targets based on the reference year 2005, to be met from 2020 onwards: 63% for SO2, 36% for NOx and 7% for NH3;
  • The Decree-law No. 84/2018 that transposes the new Ceilings Directive (Directive (EU) 2016/2284) establishes new commitments to reduce atmospheric emissions for 2020, with reference to 2005, in line with the CLRTAP Decision 2012/2 and new emission reduction commitments, to be complied with from 2030 onwards: 83% for SO2, 63% for NOx and 15% for NH3;
  • The ceilings established for 2010 by the previous Directive remained valid until December 31, 2019;
  • The national objectives for this area are:
    • To comply with international and European agreements on the reduction of emissions of pollutants into the air;
    • To ensure that the sectoral measures necessary to achieve the objectives of reducing air emissions are taken and implemented.
Progress analysis:
Last update: 
Saturday, 28 August, 2021