Frequently Asked Questions (FAQs) | National Atmospheric Emissions Inventory

Please see below a list of Frequently Asked Questions (FAQs). Click on the arrow to reveal the answers.

Note: Qs 1-first section concerns (FAQs 1 – 13 concern the whole NAEI – i.e. both air quality and greenhouse gas emissions; FAQs 14 – 19 focus on issues largely affecting greenhouse gas emissions data. FAQs on UK GHG emissions statistics are published by UK government.

1. When will the latest inventory data be published?

The NAEI presents an “end of year account” for UK emissions, based on national statistics and other datasets for a given year “N”. Common with other national inventories, the publication of national totals starts in February of year “N+2”, with all sub-national and other outputs released for year N after that, i.e. year 2024 emissions data are first published in year 2026. A data release schedule for data for a typical year is shown in the table below.

AQ/GHG	Output	Published	Where
GHG	UK territorial greenhouse gas emissions statistics	February	UK government
AQ	ENV01 - Emissions of air pollutants	February	UK government
AQ	Annex I: Sectoral UK Emissions for 1990-20XX	February	NAEI Website
AQ	UK Informative Inventory Report (IIR)	March	NAEI Website
AQ	Projected Air Quality Emissions Data: 2025-2050 (Annex IV)	March	NAEI Website
AQ	UK Air Quality Pivot Table: 1970-20XX	March	NAEI Website
GHG	UK Greenhouse Gas Pivot Table - by Source	March	NAEI Website
AQ	UK Air Quality Inventory Data: 1990-20XX - Machine Readable CSV Files	April	NAEI Website
AQ	Projected Air Quality Emissions Data: 2025-2050 (Annex IV) - Machine Readable CSV File	April	NAEI Website
GHG	UK Greenhouse Gas Inventory: 1990 to 20XX (also known as National Inventory Document (NID))	April	NAEI Website
GHG	UK Greenhouse Gas Pivot Table - by End User	April	NAEI Website
GHG	UK Greenhouse Gas Inventory: 1990-20XX - Machine Readable CSV Files	April	NAEI Website
Both	UK Emissions Data Selector	April	NAEI Website
Both	Emission Factor Selector	April	NAEI Website
GHG	Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990-20XX	June	NAEI Website
GHG	Local authority and regional GHG emissions statistics	June	UK government
GHG	Interactive Local Authority GHG Map: 2005-20XX	Summer	NAEI Website
Both	UK Emissions Interactive Map: 20XX	Summer	NAEI Website
Both	Emissions from Point Sources: 2005-20XX	Summer	NAEI Website
Both	Gridded Emissions Data: 2005-20XX	Summer	NAEI Website
AQ	Air Pollutant Inventories for England, Scotland, Wales and Northern Ireland: 2005-20XX	September	NAEI Website

Note that the time-lag in publication (from end of the latest year of inventory estimates to the date of publication) is due to:

(i) the need for finalised statistics for year N to be used as NAEI model inputs per emission source,

(ii) the time needed for rigorous compilation and quality assurance of the UK data – these are national Official statistics with associated Quality Assurance/Quality Control (QA/QC) routines and data governance requirements, and

(iii) the need to align with national official statistical releases and international reporting schedules.

2. What are the main differences between the GHG inventory and air quality pollutant inventory?

The key differences in scope between the GHG and AQ inventories are given in the table below.

	GHG Inventory	Air Pollutant Inventory
Scope of pollutants	Carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF₆), nitrogen trifluoride (NF₃). The last four gases are collectively referred to as fluorinated gases or F-gases. Note, only primary emissions are considered in the inventory. Precursor gases are reportedly separately but not included in national totals.	Particulate matter (PM), nitrogen oxides (NOx), sulphur dioxide (SO₂), ammonia (NH₃), non-methane volatile organic compounds (NMVOCs), carbon monoxide (CO), metals, polycyclic aromatic hydrocarbons (PAHs) Note, only primary emissions are considered in the inventory.
Territorial coverage	Under the UNFCCC - UK, UK Crown Dependencies (Jersey, Guernsey, Isle of Man) and UK Overseas Territories (Bermuda, Cayman Islands, Falkland Islands, Gibraltar). Under the Paris Agreement - UK, UK Crown Dependencies (Jersey, Guernsey, Isle of Man) and UK Overseas Territories (Gibraltar). Under the Climate Change Act – UK	Geographical scope of emissions under both CLRTAP (for all of the most recent reduction obligations for the different pollutants under review by the Implementation Committee) and NECR is UK and Gibraltar.
Temporal coverage	Data are typically available from 1990 through to the latest inventory year. Some datasets include data back to 1970; however, data prior to 1990 is not routinely updated.	Data are typically available from 1990 through to the latest inventory year. Some datasets include data back to 1970; however, data prior to 1990 is not routinely updated.
Reporting taxonomy	International: UNFCCC Common Reporting Tables (CRT) Domestic: Territorial Emissions Statistics (TES) sectors. Supplementary tables are also published showing emissions by energy end user TES sector and Standard Industrial Classification (SIC)	International: UNECE Nomenclature For Reporting (NFR19) codes UK: Defra Statistics Sectors, Standard Industrial Classification (SIC)
Reporting mechanisms	UNFCCC; Paris Agreement; Climate Change Act	UNECE; CLRTAP; NECR
What is excluded from national totals for compliance with legal targets?*	Emissions from international aviation and international shipping are reported as “memo items” at UK level.	Emissions from the cruise phase of domestic and international aviation are excluded from UK totals (whereas the emissions from take-off and landing cycles of all flights ARE included).

* For more information on GHG emission sources and sinks excluded from GHG reporting that are not relevant to the AQPI, then section 1.7 of the NID includes an assessment of completeness.

For more information on AQ emission sources excluded from AQ reporting that are not relevant to the GHGI, then section 1.8 of the IIR includes an assessment of completeness.

3. Where can I find details of the methodologies used in the NAEI?

A description of the methodologies used to estimate UK emissions in the NAEI are given in the Informative Inventory Report ((IIR), for air pollutant reporting) and the National Inventory Document ((NID), for GHG reporting). Detailed methodology reports on specific improvements are also available from the 'reports' sections for AQ and GHG respectively.

Further details of the spatial methodology are available in UK Spatial Emissions Methodology Report.

4. What units are used in NAEI datasets?

The NAEI typically reports emissions in kilotonnes (kt) for most pollutants. However, some pollutants are reported in different units. For example, certain metals (e.g. calcium, magnesium, potassium and sodium) are reported in tonnes (t), while polycyclic aromatic hydrocarbons (PAHs) are reported in kilograms (kg). Additionally, dioxins (PCDD) and furans (PCDF) are reported in terms of mass but weighted according to the toxicity of the individual constituent compounds. This is expressed using the International Toxic Equivalent (I‑TEQ), which applies toxicity equivalency factors to the congener mixture. The concept of TEQ is explained further in the UNEP Toolkit (UNEP, 2013).

Units are always clearly specified in available datasets, either in a dedicated ‘Units’ column or as part of the column heading.

Emission factors are a measure of the mass emission to atmosphere per unit activity, for a given emission source. The activity data varies according to each emission source, and this impacts the units in which the emission factor are expressed.

For example, for fuel combustion sources the activity data are typically the amount of a fuel combusted (which may be in mass, energy or volume terms); therefore, the pollutant emission factors are expressed as kilotonnes of pollutant per unit activity, typically kt / Mt or kt / TJ net.

[where Mt = megatonnes of fuel used; TJ net = terajoules of fuel used on a net energy basis]

For other emission sources, different units may be used to express emission factors, for example:

Kt pollutant per # of livestock, by livestock type
Kt pollutant per unit land area, e.g. kt / hectare
Kt pollutant per unit of production of an industrial product (e.g. per Mt cement clinker, per Mt steel produced)

For greenhouse gases, as well as deriving / reporting mass emissions per individual GHG, it is also often required to report the aggregate of all GHG emissions using carbon dioxide equivalent (CO₂e). These can be derived by applying GHG-specific Global Warming Potentials (GWPs). See FAQ question 15 for further details.

For air quality pollutants, there is no equivalent approach to aggregate across different pollutants, as they have different physical properties and health or environmental impacts. Emissions of each pollutant must therefore be assessed and reported separately, applying the emission factors appropriate for that pollutant.

5. What data sources does the NAEI use?

The NAEI aims to provide emission estimates for all known significant anthropogenic sources and sinks; to do this we draw upon hundreds of different data sources, ranging from Official Statistics (on energy use, transport activity, agricultural production, industrial production and so on) to regulatory reported data, to bespoke datasets obtained via individual trade associations, companies and research agencies.

If you are interested in understanding the data used for a specific emission source, then please refer to the two main national reports that are published annually, the National Inventory Document (NID), for GHG reporting and the Informative Inventory Report (IIR), for air pollutant reporting.

Some of the key datasets that we use for the NAEI include:

The Digest of UK Energy Statistics (DUKES), published annually by DESNZ and periodic publications of Energy Trends
Environmental regulator data (Environment Agency, SEPA, NRW, NIEA, OPRED), including:
- UK Emissions Trading System (UK ETS) data
- EPR/PRTR/IED Pollution Inventory data
- Environmental and Emissions Monitoring System (EEMS)
- Local Authority “Part B” emissions data
Transport statistics from DfT
Civil Aviation Authority flight movement data
Industrial production and emissions data, such as from major petrochemical and chemical manufacturers, mineral and metal industries.
Agriculture statistics from Defra and Agriculture and Horticulture Development Board (AHDB), including:
Research studies commissioned by Defra, DESNZ and others
International inventory methodological guidance such as
- GHG inventory guidelines from the IPCC (e.g. for 2006 and 2019)
- Air pollutant inventory guidelines from EMEP/EEA
- Source-specific guidance and emission factor resources, including from industrial publications such as BREF notes, USEPA AP-42 and the API Compendium (PDF 10.7 KB)

6. How can I access the underlying emission factors or activity data?

Emission factors can be downloaded from the Emissions Factor Data Selector. To download activity data go to the UK emissions data selector and select the ‘Include Activity Data’ check box at the bottom of the page.

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There are some instances where emission factors or activity data cannot be shared due to confidentiality restrictions, particularly where a sector corresponds to a single industrial site. In such cases, the activity data and emission factors are excluded from the data set. If emissions are considered to be confidential, then these are aggregated with other data to prevent the disclosure of commercially sensitive information.

7. What emission factors should I use for transport/vehicles?

The NAEI provides emission factors for road transport on the website (https://naei.energysecurity.gov.uk/emission-factors/emission-factors-transport). For company greenhouse gas reporting, we recommend using the DESNZ Greenhouse Gas Conversion Factors, which are derived from NAEI data but formatted specifically for organisational reporting (https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2025Government conversion factors for company reporting of greenhouse gas emissions - GOV.UK).

8. How should I reference NAEI data?

For citing NAEI outputs, if you are referencing a report, please refer to the ‘Suggested reference’ section within each report. If there is no ‘suggested reference’ section, for example, if using the Harvard referencing system, it is recommended to use the following format:

Authors (Year of Publication). [Title of report]. National Atmospheric Emissions Inventory / WSP Consortium. Available at: [URL]

For example:

Elliott, M., Ingledew, D., Richmond, B., et al. (2026). UK Informative Inventory Report (1990 to 2024). National Atmospheric Emissions Inventory / Ricardo Consortium. Available at: https://naei.energysecurity.gov.uk/reports/uk-informative-inventory-report-1990-2024

If you are referencing a dataset, it is recommended to use the following format:

National Atmospheric Emissions Inventory (Year of publication). [Name of dataset]. Available at: [URL] (Accessed: [insert date]).

For example:

National Atmospheric Emissions Inventory (2025). Emission Factors Database. Available at: https://naei.energysecurity.gov.uk/emission-factors/emission-factors-database (Accessed: 26/02/2026).

9. How can I offer data or feedback that could be incorporated into the NAEI?

If you have any data that could improve NAEI methodologies or validate assumptions, please contact us at naei.helpdesk@wsp.com.

The NAEI seeks to estimate emissions from all anthropogenic sources and sinks. To do this, we rely on the best available UK and global data and peer reviewed research that is available. We strive to continually improve and welcome engagement and improvements suggestions from across industry, researchers and other stakeholders. Improvement suggestions are added to the NAEI’s central feedback log, which is reviewed annually to inform potential improvement items. These items are then prioritised each Spring against a set of agreed criteria, including how effectively they:

boost data quality and robustness,
maximise impact of the inventory,
futureproof the inventory,
support government policy,
and/or strengthen the user experience.

All improvement suggestions are considered by DESNZ and Defra for implementation, subject to resources available.

10. How do I interpret the emissions shown on the NAEI interactive map?

The NAEI interactive map (https://naei.energysecurity.gov.uk/emissionsapp/) shows emissions in tonnes per 1x1km grid square. The colour scale indicates emission intensity, with red areas showing higher emissions. Note that these are pollutant emissions ( i.e. the mass of pollutant released into the air per year) rather than pollutant concentrations ( i.e. the ambient concentration of the pollutant in the air). For ambient air quality pollutant concentration data, please refer to the UK Air Information Resource (UK-AIR). Details of the spatial methodology are available in UK Spatial Emissions Methodology Report.

11. How can I find emissions data for one or more of the constituent countries of the UK (i.e. for England, Scotland, Wales, or Northern Ireland)?

Devolved Government (DG) data are available on the NAEI website under "Greenhouse Gas Inventories for England, Scotland, Wales & Northern Ireland" and "Air Pollutant Inventories for England, Scotland, Wales & Northern Ireland". These datasets provide annual mass emissions to atmosphere per pollutant, per source sector and per constituent country of the UK.

It should be noted that the combined DG inventories do not necessarily sum to the UK total. This is because certain emission sources cannot be attributed to an individual devolved government and are therefore reported as unallocated sources (e.g. offshore oil and gas). Additionally, the geographical scope of the DG inventories will not align with data reported under international reporting requirements as DG inventories do not include any Crown Dependencies (CDs) or Overseas Territories (OTs).

12. How can I access local authority level emissions data?

Local authority GHG emissions data are published on the GOV.UK website. You can also use the NAEI emissions map (https://naei.energysecurity.gov.uk/laghgapp/) to select and download GHG data for specific local authority boundaries.

In addition, the Local Air Quality Management Helpdesk is available to local authorities in the UK for questions on air quality monitoring, modelling and emissions inventories. Telephone: 0800 032 7953 E-mail: laqmhelpdesk@bureauveritas.com.

13. How can I access point source emissions data and what is included in the dataset?

Point source emissions data are available from the NAEI website under "Emissions from NAEI large point sources" (https://naei.energysecurity.gov.uk/data/maps/emissions-point-sources). The dataset provides annualised total emissions of a wide range of pollutants from regulated industrial sites across the UK. Data are published as a time series from 2005 to the latest inventory year, and the latest year is available to download as an Excel file at the bottom of the page.

Point sources are individual industrial or commercial installations with emissions reported at a known location (i.e., with grid references), allowing them to be mapped directly. Reported emissions may account for all or part of the national total for a given sector:

In sectors where all major facilities report emissions (e.g., large power stations), point sources represent the full national total.
In sectors where only larger installations report (e.g., combustion in industry), the remaining emissions are mapped separately as area sources, not point sources.

Point source emissions in the NAEI are compiled using several data sources and approaches:

Regulated industrial sites reporting to the Pollution Inventory (PI), Welsh Emissions Inventory (WEI), Scottish Pollutant Release Inventory (SPRI), Northern Ireland Environment Pollution Inventory (PIV), European Pollutant Release and Transfer Register (E-PRTR), or direct from process operators or trade associations.
EU Emissions Trading Scheme (ETS) and UK ETS registered installations.
Local Authority regulated sites under Local Authority Pollution Control/Air Pollution Control (LAPC/APC) where emissions are estimated by WSP based on detailed historical site data collected from regulators in the late 1990s and early 2000s.
Modelled point sources, where emissions are modelled by distributing national emission estimates over the known sources on the basis of capacity or some other 'surrogate' statistic.

Point source datasets only include emissions from installations that meet regulatory reporting thresholds or can be reliably modelled at site level. Smaller or unregulated sources are not included as individual point sources; these emissions appear within the NAEI’s area source mapping instead.

If you would like more information or have specific data needs, please email naei.helpdesk@wsp.com, using the subject line: “FAO: GIS team”.

14. What does "Carbon Dioxide as Carbon" mean and how do I convert this to CO₂?

“Carbon Dioxide as Carbon" shows only the weight of the carbon (C) part of the carbon dioxide (CO₂) emissions. To convert from C to CO₂, multiply by 44/12 (approximately 3.67), which is the ratio of the molecular weights of CO₂ to C. This conversion accounts for the molecular structure where one carbon atom (atomic weight 12) combines with two oxygen atoms (atomic weight 16 each).

“Carbon dioxide as Carbon” is frequently used to express emission factors, within UK publications as well as within international inventory guidance. For example, CO₂ data downloaded from the UK emissions data selector and the Emissions Factors Data Selector are given in units of Carbon Dioxide as Carbon.

15. How do I convert from mass of pollutant to mass of CO₂e?

For Greenhouse Gases (GHGs), emissions can be reported either as the mass of the pollutant or as the mass of the pollutant expressed as carbon dioxide equivalent (CO₂e).

Expressing GHGs as carbon dioxide equivalents enables comparison of the impact of different GHGs and also the aggregation of total GHGs across emissions of all individual GHGs.

The UK is required to report total greenhouse gas emissions using the GWP100 metric, which represents international best practice. This metric has been adopted by the United Nations Framework Convention on Climate Change (UNFCCC) for reporting greenhouse gas emissions globally, including under the Paris Agreement, to which the UK is a Party. Additionally, the UK uses GWP100 for reporting under the Climate Change Act and for tracking progress against legally binding Carbon Budgets. This ensures consistency between domestic and international reporting standards. The UK will take an active role in UNFCCC discussions on common metrics when the agenda item is revisited in June 2027. Our approach will continue to be led by the best available science and international consensus. 

The table below presents the AR5 GWPs applied per individual GHG in UK inventory reporting:

Pollutant	GWP Conversion Factor (AR5) (IPCC AR5, 100-year horizon)
CO₂	1
SF₆	23500
CH₄	28
N₂O	265
HFC-152a	138
HFC-134a	1300
HFC-23	12400
HFC-32	677
HFC-125	3170
HFC-143a	4800
HFC-227ea	3350
HFC-43-10mee	1650
HFC-134	1120
CF₄	6630
C₂F₆	11100
C₃F₈	8900
C₄F₈	9540
C₄F₁₀	9200
HFC-245fa	858
HFC-365mfc	804
NF₃	16100

16. How are emissions from biofuels accounted for in the inventory? Do biofuels feature in the inventory?

Emissions from biofuels are treated differently depending on the emitted gas but with specific consideration for their carbon cycle.

Consistent with international inventory guidance, biogenic carbon dioxide emissions from biofuel combustion do not count towards UK GHG emissions inventory totals but are reported as a memo item in the GHG inventory (see section 1.7.4.3 of the National Inventory Document). For example, the associated carbon stock changes accounted for in the emissions are accounted for in the Land Use, Land Use Change and Forestry (LULUCF) sector.

For all other pollutants (i.e. except carbon dioxide), emissions are reported in the UK inventory in the same way as for any other fuel combustion emission source in the inventory. Furthermore, emissions from blended fuels (partly fossil, partly biogenic) are split and reported separately with carbon dioxide emissions from the fossil component added to the national total.

17. How are agricultural emissions calculated?

For details of how the emissions from agriculture are estimated, please see the relevant chapters within the two main national reports that are published annually:

Additionally, as agriculture is the key sector for ammonia (NH₃) emissions, a separate Inventory of Ammonia Emissions from UK Agriculture report is published annually.

The UK agriculture GHG and air pollutant emissions are compiled and reported via a Defra-funded project led by ADAS, including technical expertise from across UK agriculture experts from Rothamsted Research, the UK Centre for Ecology and Hydrology, WSP and Cranfield University.

As an overview, agriculture emissions are estimated by applying methods that are consistent with the prevailing IPCC and EMEP/EEA guidelines, with higher tier (i.e. UK-specific) methods and emission factors applied for key categories, such as for enteric fermentation and manure management from beef and dairy cattle.

The methods draw upon latest UK statistical evidence on sector activities, including the June Agricultural Survey, which delivers livestock numbers, crop production / areas, the Cattle Tracing System (CTS) and the British Survey of Fertiliser Practice (BSFP). Further, where data are available, information is used at devolved government level.

Defra funded a major programme of development of UK-specific evidence between 2010 and 2015 (methods and emission factors), via the GHG Research Platform (see: https://www.theccc.org.uk/wp-content/uploads/2018/08/PR18-Chapter-6-Annex-The-Smart-Agriculture-Inventory.pdf (PDF 542 KB) which led to the development of the current UK agriculture inventory model. Improvements started to be implemented in the agriculture inventory in 2016 and are ongoing as new data become available and methodologies develop.

The UK data and methods are under continuous improvement, with current improvement research focusing on how the inventory can represent latest evidence on livestock energy maintenance requirements, the impact of methane reducing feed products (MSFPs) and latest mitigation practices being implemented across the sector.

If you have any questions or feedback, you can send queries through to the NAEI helpdesk (naei.helpdesk@wsp.com).

18. How does the NAEI handle waste incineration and Energy from Waste (EfW) emissions?

The NAEI reports waste-related combustion emissions under several categories, depending on the type of waste, whether energy recovery occurs, and the regulatory status of the facility.

Currently, all municipal solid waste (MSW) incineration plants in the UK operate as energy recovery facilities. As a result, emissions from these facilities are reported under CRT/NFR 1A1a (public electricity and heat production) of the energy sector, not under the waste sector. Emissions from MSW incineration in Jersey and the Isle of Man are also reported under 1A1a.

For modern EfW plants, the NAEI reports emissions using a fossil/biogenic split based on waste composition data from the Digest of UK Energy Statistics (DUKES):

Biogenic Carbon Dioxide (CO₂) is reported as a memo item.
For all other gases (GHG and air pollutants), emissions are included in national totals regardless of waste origin.

Emissions from waste incineration without energy recovery are reported in the waste sector. The following waste types are reported under category 5C1 (waste incineration), because there is no identified evidence of energy recovery at these installations: 

clinical waste in Cayman Islands, Falkland Islands, Gibraltar, Guernsey, and Jersey 
sewage sludge
animal carcasses

The UK reports emissions under 5C2 for open burning, such as:

small scale waste burning
bonfires
accidental vehicle or building fires (For GHG, or 5E (Other waste) for air pollutants)

Emissions from vegetation fires are reported under sector 4 for greenhouse reporting, and as a memo item for air quality reporting.

On-site burning of agricultural residues, such as crop residue burning, is not counted under 5C, but instead reported separately under category 3F.

19. Why are ozone depleting substances excluded?

Ozone depleting substances already tracked and reported under the Montreal Protocol are excluded from greenhouse gas reporting (see section 1.7.4.4 of the National Inventory Document).