The UK National Atmospheric Emissions Inventory

The UK National Atmospheric Emission Inventory (NAEI) is compiled by the National Environmental Technology Centre on behalf of the Department of the Environment, Transport and the Regions’ (DETR) Air and Environment Quality Division and the devolved administrations. Related work on greenhouse gas emissions is also conducted for the Global Atmosphere Division of the Department. The NAEI is the standard reference air emissions inventory for the UK and includes emission estimates for a wide range of important pollutants including greenhouse gases, regional pollutants leading to acid deposition and photochemical pollution, persistent organic pollutants and other toxic pollutants such as heavy metals. The full range of pollutants is summarised in Table 1.1. Where possible, estimates are presented for 1970-1998. However, for some pollutants, e.g. ammonia, there is insufficient information to produce a 1970-1998 time series and estimates are presented from 1990-1998.

Emission inventories serve several important functions, as explained in Section 1.1. The following highlight several of the more important uses of the UK NAEI:

1. Provision of Public Information- The data from the NAEI is made available to the public in various forms (see Section 1.2.3). The aim is to make information available in an easily understandable format, informing the public of emissions in their area as well as making national emissions data available. The NAEI is paid for by tax payers money, through the Government, and consequently it is important to maintain a high public profile and accessibility to the work.
2. Development of policy
• Identification of Primary Sources- The NAEI compiles emissions from all anthropogenic and natural sources (where information allows). Consequently it is simple to determine which source sectors are the major emitters of individual pollutants.
• Temporal and Spatial Trend Assessment- The NAEI provides information to allow temporal trend analysis as it is compiled annually (from 1970 for most pollutants). In addition, UK maps are generated for several of the pollutants, allowing spatial trends to be assessed.
• Inventory Comparisons- Mapped emission inventories exist for a number of cities across the UK. In some cases the techniques used to compile these emission inventories differ from the NAEI. As a result comparison with the NAEI highlights the potential strengths and weaknesses of the different techniques.
• National Modelling Studies- The NAEI is used in a variety of modelling studies investigating spatial and temporal trends in deposition and concentration of pollutants. Furthermore, it is possible to use the NAEI alone to investigate the impact on emissions of particular future policy scenarios.
• Local Support- Data from the NAEI is frequently used by Local Authorities to support air quality assessments, and aid the generation of local policy.


3. National and International Reporting- The NAEI provides the official air emissions estimates for the UK. National and International reporting requirements are given in more detail in the following Sections.
4. Progress on Complying with National and International Commitments- The annual inventory provides an important assessment tool for policy makers. The inventory is used to monitor progress towards emission limits and ceilings at both the national and international level, and is therefore an important tool in assessing the effectiveness of existing policy measures.

 

International Commitments

The NAEI provides the UK air emission data for submission to United Nations Economic Commission for Europe (UN/ECE) and the United Nations Framework Convention on Climate Change (UNFCCC). Under the UNFCCC, the UK is committed to developing, publishing and regularly updating national emission inventories of greenhouse gases using reporting guidelines from the Intergovernmental Panel on Climate Change (IPCC). The inventories for both direct greenhouse gases (carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride) and indirect greenhouse gases (nitrogen oxides, carbon monoxide and non-methane volatile organic compounds) are drawn from the UK NAEI emissions data included in this report. Likewise, NAEI estimates of emissions of nitrogen oxides, carbon monoxide, ammonia, sulphur dioxide, NMVOC, persistent organic pollutants and heavy metals are submitted to UN/ECE under the Convention on Long-Range Transboundary Air Pollution (LRTAP). NAEI data are also provided to international emission inventory activities such as the EC’s CORINAIR and EUROSTAT inventories. The UK inventory team play an important role in the development of international guidelines by the European Environment Agency and the UN/ECE which aims to achieve a consistent set of good quality inventories for all European countries. More information may be found at the EMEP and UNFCCC websites at:

http://www.emep.int/ and http://www.unfccc.de/

Not all international reporting of emissions are drawn from the UK NAEI. One exception is the EC’s forthcoming EPER (European Polluting Emissions Register) which arises from the IPPC Directive. The Environment Agency’s Pollution Inventory (PI) will provide the UK data for the EPER.

National Information

The NAEI is a key database used to provide air emissions data to the public, UK Government, the devolved administrations, Local Authorities and private sector organisations. Many of the specific policy uses have been outlined above, but there are a number of other ways in which the data is used. Several are given below:

• A significant amount of time is spent providing detailed emission estimates, output from scenario analysis and supporting information to the DETR and the devolved administrations. This information is required for a wide variety of uses; long-term policy support to specific short-term issues.
• A great deal of information is made available to other organisations working on DETR projects, or projects for the devolved administrations. This ensures a high level of consistency and efficiency.
• Mapped emission inventories for the UK are generated on a on a 1x1km scale. These are frequently used as a starting point for many local emission inventories.
• Emission estimates for point sources and emissions arising from the surrounding area are used in modelling studies as part of Environmental Impact Assessments by developers and their consultants.
• There is a two way exchange of data with Trade Associations. This ensures that the NAEI and the Trade Associations can arrive at emission estimates that are truly representative.
• Point sources and emissions arising from the surrounding area are used in modelling studies as part of Environmental Impact Assessments by developers and their consultants.
• Emission factor data is fed into the UK’s Emission Factor Database for access by Local Authorities.

 

Table 1.1 Pollutants Covered by the Inventories

Pollutant		Range of Estimates	Type of Pollutant*
Carbon Dioxide	CO2	1970-1998	G
Methane	CH4	1970-1998	G
Nitrous Oxide	N2O	1990-1998	G
Nitrogen Oxides	NOx (NO2 + NO)	1970-1998	NAQS, AC, IG, O
Sulphur Dioxide	SO2	1970-1998	NAQS, AC, IG
Carbon Monoxide	CO	1970-1998	NAQS, O
Non-Methane Volatile Organic Compounds	NMVOC	1970-1998	NAQS, O, IG
Black Smoke	BS	1970-1998	NAQS
Particulates < 10 m m	PM10	1970-1998	NAQS
Ammonia	NH3	1990-1998	AC
Hydrogen Chloride	HCl	1970-1998	AC
Lead	Pb	1970-1998	NAQS, TP
Cadmium	Cd	1970-1998	TP
Mercury	Hg	1970-1998	TP
Copper	Cu	1970-1998	TP
Zinc	Zn	1970-1998	TP
Nickel	Ni	1970-1998	TP
Chromium	Cr	1970-1998	TP
Arsenic	As	1970-1998	TP
Selenium	Se	1970-1998	TP
Vanadium	V	1970-1998	TP
Polyaromatic Hydrocarbons	PAH	1990-1998	TP
Dioxins and Furans	PCDD/F	1990-1998	TP
Polychlorinated Biphenyls	PCB	1990-1998	TP
Lindane (gamma-HCH)	HCH	1990-1998	TP
Pentachlorophenol	PCP	1990-1998	TP
Hexachlorobenzene	HCB	1990-1998	TP
Hydrofluorocarbons	HFC	1990-1998	G
Perfluorocarbons	PFC	1990-1998	G
Sulphur Hexafluoride	SF6	1990-1998	G

*G Greenhouse gas

IG Indirect greenhouse gas

O Ozone precursor

AC Acid gas

NAQS National Air Quality Standard/Local Air Quality Management pollutant

TP Heavy metals and POPs are generally referred to as "Toxic Pollutants" (although other pollutants also have toxic properties)

 

The NAEI is compiled on an annual basis, each year the latest set of data are added to the inventory and the full time series are updated to take account of improved data and any advances in the methodology used to estimate the emissions. Updating the full time series is an important process as it ensures that the entire dataset uses the methodology that is the most current, and hence considered to give the most accurate results and the most accurate indication of temporal trends. The new data are then reported to UN/ECE, UNFCCC and other international fora. This annual cycle of activity is represented schematically in Figure 1.2.

Figure 1.2 The Annual NAEI Cycle



 

This report presents the definitive 1998 data from the NAEI and is the latest in a series of annual reports published by the NAEI (Eggleston, 1988; Eggleston and Munday, 1989; Munday, 1990; Leech, 1991; Gillham et al 1992; Gillham et al 1994; Salway et al 1996, 1996a, 1997, Salway 1999, Salway et al 1999, Goodwin et al 1999). This report discusses trends in pollutant emissions, the accuracy of the emission estimates and in many cases the pattern of their spatial disaggregation within the UK. A detailed description of the methodology used in the compilation of the data is given in Appendix 1, and recent methodological improvements to the inventory, and planned developments are both included in Appendix 2. Mapping methodologies, NMVOC speciation and other detailed pollutant emissions are also included in Appendices.

Information Dissemination

Data from the NAEI is made available to national and international bodies in a number of different formats- as explained in Sections 1.2.1 and 1.2.2. An annual report is produced, giving the most recent emissions data and other information such as: temporal trends, new pollutants and methodology changes. The NAEI team also hold seminars with representatives from industry, trade associations, UK Government and the devolved administrations.

In addition there is a continuous drive to make information available and accessible to the public. A large amount of information is made available on the internet. The NAEI web pages may be found at:

/netcen/airqual/index.html

These web pages are arranged into a number of different categories which fall under the following headings:

• Annual Report:- The most recent NAEI annual report is made available in electronic format.
• Methodology:- The methods used for the compilation of the NAEI are given.
• Datasets:- Various datasets are made available, the most comprehensive being a queriable database of the NAEI emission estimates.
• Emissions Maps:- Emissions of pollutants are given in the form of UK maps. These maps give emissions of various pollutants on a 1 x 1 km resolution. It is possible to zoom in to areas of interest, and access the source data for the maps.
• Post Code Search:- This search facility enables visitors to the site to enter their post code, and obtain emissions data concerning the major sources in the vicinity.

The web site is constructed so that the air emissions are placed in context. In addition there are numerous links to locations explaining technical terms, pages giving airborne pollutant concentrations and why there is an interest in particular pollutants. In particular there are links to the various DETR pages containing comprehensive measurement data on ambient concentrations of various pollutants.

 

Continuous Improvement and Basic Methodology

Throughout the compilation of the inventory considerable effort has been made to ensure both consistency with other national statistics and that all available data sources are considered. Hence, the source data are drawn from a wide range of sources. One source is the provision by the Environment Agency of emissions data, since 1988, on SO₂ and NO_x emissions from large combustion plant, and more recently the emissions data for Part A Processes in the Pollution Inventory. Where specific point source emission data are unavailable, emissions are estimated from other activity data such as fuel consumption, distance travelled, production or some other statistical data that is directly related to the emissions. Emission estimates are calculated by applying an emission factor to an appropriate activity statistic.

That is:

Emission = Factor × Activity

Emission factors are generally derived from measurements on a number of sources assumed to be representative of a particular source sector. The resulting emission factor may then be applied to similar sources within the sector. However, as mentioned above, some sectors are particularly well characterised and individual point sources within the sector may report a specific emission, which is regarded as being more reliable. This is often the case with sectors incorporating large point sources (an example being the Power Station sector). The inventories presented here are generated using a combination of reported point source emissions, and emissions calculated using emission factors. Methodology improvements are applied to all years (where appropriate).

For many of the pollutants, the major source of emission is generated from fossil fuel combustion. As a result fuel consumption statistics feature prominently in the calculation of these emission estimates. It is important to consider the difference between consumption and deliveries when making use of fuel statistics. Most readily available statistics refer to deliveries which for many source categories relate closely to actual consumption of fuel. However, where fuel can be stockpiled, deliveries and consumption may differ significantly. This is just one example of having to ensure that the available data is correctly interpreted, and used in the most appropriate way to arrive at representative emission estimates.

Emissions from sources such as industrial processes, farm animals and motor fuel evaporation require different statistics; in these cases data on process output, population and motor fuel sales are appropriate.

In other cases, where emissions are more complex, further refinements or an alternative methodology is required. For example, consider the emissions from road vehicles. An obvious activity indicator would be distance travelled, but emissions per unit distance travelled will depend on: vehicle type, vehicle age, engine size, average speed and several other parameters. Clearly the methodology rapidly becomes complicated. A separate road transport model is used for calculating the emissions given in the NAEI.

During 1998, particular emphasis has been placed on improving several areas of the emission inventory. Of the pollutants considered under the NAEI, significant improvements have been made to the speciation of NMVOCs and POPs. Consequently the source sectors which were targeted for improvement have been the industrial and chemical processes producing NMVOCs, and the sectors generating POPs. In addition, the emissions estimates from the road transport sector have been refined by obtaining more detailed fleet data for several vehicle classes and speeds. At a more general level there is also a continued drive to use data which most accurately represents the source. Emission factors and activity data are assessed each year to identify whether more appropriate information has become available. The resulting update of the methodology for 1998 is given in Appendix 3. The current methodology used for generating emission maps is also included in this report in Appendix 2. It should be noted that this methodology is for mapping only, and does not generate total emission estimates- merely spatially disaggregates them in the most appropriate way.

The following sections of the report present the NAEI emission estimates for the UK. They have been divided into five groups, reflecting the national and international activity relating to atmospheric pollution, namely greenhouse gases, National Air Quality Strategy pollutants, stratospheric ozone depletors, acidifying gases and tropospheric ozone and other hazardous air pollutants. Each section includes a discussion of the importance of the pollutants concerned, presents time series emission data, and a discussion of the data trends and the accuracy of the emission estimates.

Offshore Emissions

Offshore emissions are included in the NAEI, and hence in estimates presented here. However, it is difficult to identify an offshore total for many of the pollutants as the emissions occur from a number of different sectors under the UN/ECE reporting format. For example, CH₄ emissions from offshore platforms will arise from a number of activities. Emissions may be included under "Extraction and Distribution of Fossil Fuels", however other emissions may fall within the "Waste Treatment and Disposal" category (e.g. venting of the CH₄). Emissions from fuel combustion in shipping fall into the "Other Mobile Sources and Machinery" sector. Appendix 4 gives an explanation of the UN/ECE reporting framework and indicates which source category emissions are reported under.