Background Notes

Environmental Accounts, Air Emissions

Introduction                        

The air emissions accounts classify emissions of greenhouse gases and air pollutants by emitting economic sector, and by 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 UNFCCC (United Nations Framework Convention on Climate Change) and under the CLRTAP (Convention on Long-Range Transboundary Air Pollution).

Revisions                            

This release incorporates revisions to the air emissions estimates previously published by the CSO, including the revisions made by the EPA to the annual national air emissions inventory.

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 the total greenhouse gas emissions for Ireland, and are included in the total of greenhouse gases in Tables 1 and 12. 

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 the fluorinated gases vary, but many are in the thousands or tens of thousands.

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.  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, inorganic fertilisers and animal manure, and power stations. 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 fuel combustion for 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 sequestration.

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.  In this case, the total emissions from this CRF/NFR code are attributed to that NACE Rev. 2 sector.  In many cases, a single CRF/NFR corresponds to more than one NACE sector.  In these cases, emissions are assigned across NACE sectors by the CSO using data on fuel use by each NACE sector.

Data for all years have been presented using the NACE Rev. 2 classification, which came into effect in 2008. 

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. 

The Environmental Protection Agency’s detailed modelled road transport emissions data are combined with CSO Road Freight Transport data, private vehicle registration data and road traffic volumes data to allocate road transport usage across NACE sectors. 

There is one CRF/NFR code for road transport in the EPA Air Emissions Inventory.  This emissions figure is generally distributed across NACE sectors using data on transport fuel use by each NACE sector. 

Road freight transport data are allocated initially by using the tonne-km data collected by the CSO.  This data allocates emissions to the main NACE sectors responsible for road freight as identified in the CSO Road Freight Transport Survey.  For the remaining unspecified sectors, emissions are attributed across NACE sectors using expenditure on transport fuel by each NACE sector.

Emissions from private cars are split into household vehicles, small Public Service Vehicles (which are assigned to NACE 49) and company cars. Emissions from buses are allocated to NACE 49.  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, the road transport emissions of a German tourist driving in Ireland are included in the inventory as territorial emissions but are excluded from air emissions accounts.

The air emissions data presented in this release are compiled using the "inventory-first" approach. This approach takes the national inventory totals as a starting point, makes a residence principle adjustment, and allocates resident emissions to NACE categories and households. The adjustment to resident emissions is challenging and data collection on this aspect of the accounts is still in development. However, in Table 14 of this release there are provisional data on transport emissions by Irish residents abroad and on transport emissions by non-residents in Ireland.

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