Background Notes

Environmental Accounts, Air Emissions

Introduction                        

The air emissions accounts classify emissions of greenhouse gases and air pollutants by emitting economic (NACE) sector, including households.

Data sources                     

The figures presented in this release are based on the air emissions inventories submitted annually by the Environmental Protection Agency (EPA) to the United Nations under the United Nations Framework Convention on Climate Change (UNFCCC) and under the Convention on Long-Range Transboundary Air Pollution (CLRTAP).

Revisions                            

This release incorporates revisions to the air emissions accounts previously published by the CSO, including the revisions made by the EPA to the annual national air emissions inventories. Data on the residence principle adjustment have been included as part of the main release for the first time. A breakdown by NACE sector of emissions by resident units is provided. The adjustment from the territorial principle to the residence principle is carried out by removing transport emissions by non-residents and by adding transport emissions by residents abroad. Air transport residence adjustment data are available for carbon dioxide only.

Greenhouse Gases

The three main greenhouse gases included in this publication are carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄). As greenhouse gas emissions from human activities increase, they build up in the atmosphere, warming it through the greenhouse effect. Because many of the major greenhouse gases stay in the atmosphere for tens to hundreds of years after being released, their warming effects on the climate persist over a long time and can therefore affect both present and future generations.

Carbon dioxide emissions are the result of burning fossil fuels such as coal, turf and petroleum for heat, power and transport. Industrial processes such as cement production also emit CO₂.

Nitrous oxide emissions arise from nitrogen fertilisers used in agriculture and a small number of industrial processes.

Methane emissions are caused by the digestive systems of ruminant animals, waste water treatment plants and landfill sites.

There are other greenhouse gases: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF₆) and nitrogen trifluoride (NF₃). The emissions from these fluorinated gases account for approximately 2% of total greenhouse gas emissions in Ireland. 

Global warming potential

Greenhouse gas emissions by different gases are compared using the global warming potentials (GWPs) for a 100-year time horizon from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report of 2007. The GWP is a measure of the global warming effect of a given mass of a greenhouse gas compared with the global warming effect of the same mass of carbon dioxide. The GWP for methane is 25 and that of nitrous oxide is 298. The GWPs of fluorinated gases vary, but many are in the thousands or tens of thousands. In this release fluorinated gas emissions are presented in units of carbon dioxide equivalent.

Greenhouse gases other than carbon dioxide may be converted into tonnes of carbon dioxide equivalent by multiplying their masses by their global warming potentials. For example, 35,000 tonnes of methane are equivalent to 875,000 (i.e. 35,000 x 25) tonnes of carbon dioxide for a 100-year time horizon. Further details are available at the IPCC website (https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10-2.html).

Air pollutants      

Sulphur dioxide (SO₂) is a gas which is formed when sulphur-containing fuels (mainly coal and oil) are burned in power stations. Household heating is one of the main sources of sulphur dioxide emissions in Ireland. Exposure to high concentrations of SO₂ can lead to breathing difficulties for people with long-term respiratory conditions such as asthma.

Nitrogen oxides (NO_x) are produced during combustion at high temperatures and by agricultural activity; the main sources in Ireland are vehicles, power stations, inorganic fertilisers and animal manure. The industrial sector is also a significant contributor to NO_x levels, particularly the cement production industry.  Exposure to NO_x is linked to adverse respiratory effects, and long-term exposure increases the risk of respiratory infection in children.

Ammonia (NH₃) emissions arise primarily from animal manure and nitrogen-based fertilisers. Exposure to high levels of ammonia may irritate the skin, eyes, throat and lungs.

Non-methane volatile organic compounds (NMVOCs) are emitted as gases by a wide array of products including paints, paint strippers, glues, adhesives and cleaning agents. They also arise as a product of incomplete combustion of fuels and are a component of car exhaust emissions. A further significant source is agricultural activity. Exposure to NMVOCs can lead to eye, nose and throat irritation, headaches, loss of coordination, nausea and damage to the liver, kidney and central nervous system.

Carbon monoxide (CO) is a colourless gas, formed from incomplete oxidation during combustion of fuel.  Emissions of CO in Ireland are mostly vehicle emissions, although fuel combustion for household heating also contributes. Concentrations of CO tend to be higher in areas with heavy traffic congestion. Carbon monoxide enters the bloodstream through the lungs, where it affects the body’s uptake of oxygen. Exposure in ambient air is most serious for people with cardiovascular diseases.

Particulate matter of median aerodynamic diameter 2.5 microns (PM_2.5), or ‘fine’ particulate matter, is composed of a mixture of solids and liquids. Depending on the source of the matter these can include acids (nitrates and sulphates), volatile organic compounds, soil, metals and dust particles. The main source of fine particulate matter in Ireland is household heating. The main sources of particulate matter of median aerodynamic diameter 10 microns (PM₁₀) in Ireland are agricultural activities, such as the use of inorganic nitrogen fertilisers, and household heating. The adverse health impact of particulate matter arises from its ability to penetrate deep into the respiratory tract.

Forestry and soil sequestration    

No adjustment has been made for reductions in greenhouse gas emissions from forest or soil (including peat) sequestration. In general, emissions from land use and land use change are excluded from the national emission inventory totals as well as from the air emissions accounts.

NACE allocation            

Emissions are distributed across NACE sectors according to the correspondences between Common Reporting Format (CRF)/Nomenclature For Reporting (NFR) codes in the Air Emissions Inventories and NACE Rev. 2 sectors. 

In some cases, there is a one-to-one correspondence between the CRF/NFR codes and a NACE Rev. 2 sector. If so, the total emissions from this CRF/NFR code are attributed to that NACE Rev. 2 sector.  However in many cases, a single CRF/NFR corresponds to more than one NACE sector.  In these cases, emissions are assigned to NACE sectors by the CSO using data on transport and non-transport energy use by NACE from the CSO's Business Energy Use survey.

Data for all years have been presented using the NACE Rev. 2 classification, which came into effect in 2008. The NACE Rev. 2 classification is a statistical classification of economic activities in the European Union.

Electricity and gas supply           

Emissions from the production of electricity and gas are allocated to the suppliers of energy rather than the end users, and so are allocated to NACE Rev. 2 division 35 (Electricity, gas, steam and air conditioning supply).

Road transport              

Road transport emissions are attributed to economic sectors according to the principal activity of the business. If the transport of passengers and freight is the principal activity of a business, then the related emissions are attributed to NACE Rev. 2 division 49 (Land transport).  If road transport is a secondary or ancillary activity to the main business, then the related road transport emissions are allocated to the main NACE division of the enterprise. 

Data on road transport fuel use from CSO's Business Energy Use were used to distribute road transport emissions across NACE sectors.

Emissions from private cars are split into household vehicles, small Public Service Vehicles (which are assigned to NACE 49) and company cars. Emissions from motorcycles are allocated to households.

Landfill waste                     

Landfill waste accounts for approximately 4-6% of methane (CH₄) emissions. The NACE Rev. 2 classification for waste treatment is NACE 37-39 (Sewerage and Waste management). Most landfill sites are owned and operated by local authorities who are categorised under NACE 84 (Public Administration and Defence).  However, all CH₄ emissions from landfill waste have been classified under NACE 37-39, as this is the NACE sector of the local unit.

Adjustment from Territorial Principle to Residence Principle

National emissions inventories present emissions of greenhouse gases and air pollutants that originate from the geographic territory of a given country. Air emissions accounts form part of the implementation by Eurostat of a series of environmental-economic accounts which are designed to be compatible with the concepts and principles of national accounts. Therefore, the air emissions accounts record emissions arising from the activities of resident units of a given national economy, regardless of where these emissions occur geographically. According to the national accounts definition of residence, an economic unit is a resident unit of a country when it has engaged for at least one year in economic activity in that territory.

For example, the road transport emissions of an Irish haulier driving in France are not included in Ireland's emissions inventory under the territorial principle, but are included under the residence principle. Similarly, the emissions arising from the activity of an Irish airline flying from England to Italy are assigned to Ireland under the residence principle but not under the territorial principle.

On the other hand, emissions from fuel sales to owners of non-Irish registered vehicle in Ireland are included in the inventory as territorial emissions but are excluded from air emissions accounts.

We compile the air emissions data presented in this release using the "inventory-first" approach. In following this approach, we take the national inventory totals as a starting point, make a residence principle adjustment, and allocate resident emissions to NACE categories and households.

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