Nature and the environment
agassn, Emissions of acidifying gases and ozone precursors, air pollution, acidifying gases (for example NOX, SO2, NH3), emissions by source (for example oil and gas production, road traffic, air traffic), emissions by industry (for example energy sector, manufacturing, primary industries)Pollution and climate, Nature and the environment

Emissions of acidifying gases and ozone precursors

As from 11 December 2018 the statistics is published with Emissions to air


Key figures

- 4,5 %

change in emissions of NOx gases in 2017 compared to the year before

Emissions of NOX, SO2, NH3, NMVOCs and CO. 1 000 tonnes. Preliminary numbers1
 2017Change in percent
 Since 19902016 - 2017
1Does not include international sea and air traffic.
Nitrogen oxides (NOX)149-24.4-4.5
Sulphur dioxide (SO2)16-68.0-2.5
Ammonia (NH3)285.90.4
Non-methane volatile organic compounds (NMVOC)153-52.1-3.6
Carbon monoxide (CO)438-50.21.1

See selected tables from this statistics

Table 1 
Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes

Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes1
Sulphur dioxide (SO2)Nitrogen oxides (NOX)Ammonia (NH3)Non-methane volatile organic compounds (NMVOC)Carbon monoxide (CO)
1Does not include ocean transport and international air transport.
All sources15.9149.328.4152.7437.8
Oil and gas extraction0.543.6:43.110.7
Manufacturing industries and mining11.
Energy supply2.01.8:1.98.2
Heating in other industries and households0.
Road traffic0.
Aviation, navigation, fishing, motor equip. etc.1.647.80.020.5113.3

Table 2 
Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes

Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes1
Sulphur dioxide (SO2)Nitrogen oxides (NOX)Ammonia (NH3)Non-methane volatile organic compounds (NMVOC)Carbon monoxide (CO)
1Does not include ocean transport and international air transport.
All sources16.3156.428.3158.3433.1
Oil and gas extraction0.645.4..46.010.8
Manufacturing industries and mining11.217.50.711.4165.3
Energy supply2.11.9..2.08.3
Heating in other industries and households0.
Road traffic0.
Aviation, navigation, fishing, motor equip. etc.1.751.30.021.2114.2

Table 3 
Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes

Emissions to air of SO2, NOX, NH3, NMVOCs and CO, by source. 1 000 tonnes1
Sulphur dioxide (SO2)Nitrogen oxides (NOX)Ammonia (NH3)Non-methane volatile organic compounds (NMVOC)Carbon monoxide (CO)
1Does not include ocean transport and international air transport.
All sources49.6197.526.8318.4878.6
Oil and gas extraction0.425.5..121.95.9
Manufacturing industries and mining37.625.20.617.3173.5
Energy supply1.11.4..0.40.6
Heating in other industries and households2.
Road traffic2.964.70.263.9400.1
Aviation, navigation, fishing, motor equip. etc.4.969.80.033.2118.5

About the statistics

Emissions of acidifying gases and ozone precursors of anthropogenic origin. They include nitrogen oxides (NOx), sulphur dioxide (SO2), ammonia (NH3), Non-Methane Volatile Organic Compounds (NMVOCs) and carbon monoxide (CO).


Definitions of the main concepts and variables

The national emission model includes four dimensions

Pollutants: The different gases/substances covered by the emission model

Technical emission sources: Stoves, ships, vehicles, flares, biological and industrial processes

Industry: Standard Industrial Classification (in Europe, called NACE)

Commodity: Different energy commodities; solid fuels (for example coal and coke), liquid fuels (diesel oil, petrol, kerosene, heavy oil etc.), gases (natural gas, landfill gas etc.), biofuel (for instance fuel wood, wood waste, pellets) and waste (hazardous waste and other waste).

Acid equivalents: Emission of acidifying substances weighed together. The following factors (Potential Acid Equivalents) are used to calculate the acid equivalents:

NO X * 1/46

SO 2 * 1/32

NH 3 * 1/17

The international agreements deal with the specific gases, not the total acid equivalents.


Other pollutants: NMVOC (non-methane volatile organic compounds) and carbon monoxide (CO).


Standard classifications

Published tables:

Emission by source

Emission by industry (NACE)

NAMEA (NACE according to Quarterly National Accounts)

Tables used in reports to UNECE/Long-Range Transboundary Air Pollutants.

Administrative information

Name and topic

Name: Emissions of acidifying gases and ozone precursors
Topic: Nature and the environment

Responsible division

Division for Energy, Environmental and Transport Statistics

Regional level

National figures.

Frequency and timeliness

Annual figures. The figures are published in two versions; in May, preliminary figures for the last year are published. In December a revised and more detailed version of the same figures are published. At th same time, revised figures for all years back to 1990 are also published. The whole time series is recalculated annually as new information becomes available.

International reporting

Annual reports to ECE (Economic Commission for Europe): Convention on Long-Range Transboundary Air Pollution (CLRTAP).


Not relevant.


Background and purpose

The purpose of the statistics is to present the total emissions from Norwegian territory, distributed by sources, industries, energy goods and counties. The statistics also show the achievement with regard to the fulfilment of international environmental obligations and national emission targets. In addition, the statistics give information to media, schools, other institutions or organizations, and the general public.

The first emission inventory was made in 1983, containing emissions of SO2 and NOX. Since then, emissions of NMVOC, NH3 and CO have also been included.

The statistics are to a great extent developed in order to cover the demands in the reporting to the protocols under the Convention on Long-Range Transboundary Air Pollution. The Norwegian Environment Agency, on behalf of the Ministry of Climate and Environment, is responsible for this reporting.

The emissions from air traffic reported under the Gothenburg protocol are slightly different from the emissions published by Statistics Norway (SSB). The emission statistics includes all emissions from domestic flights, whereas the figures reported to the protocol only include emissions from take-off and landing. For NOX, this means that the reported figures are about 1 per cent lower than what is published by SSB in the emission statistics. For the other gases the differences are lower than 1 per cent.

The statistics can also present figures on emissions from Norwegian economic activity, as defined in the national accounts. These figures include Norwegian international transport (air and sea), and are used in the environmental accounts (NAMEA) and reporting to Eurostat. As the delimitation is different, the emission figures for Norwegian territory and Norwegian economic activity will also differ.

The emission statistics are mainly based on calculations. The emission model is continuously being developed, as research on emissions to air regularly is evaluated. New emission factors are taken into use, errors in the calculations are corrected, and other improvements in the emission model are implemented. These changes lead to new, revised and more consistent time series each year, and results that are published earlier are not longer valid.

The regular compilation of the statistics is financed by Statistics Norway, but development, improvements and special demands are to a great extent financed by the Norwegian Environment Agency.

Users and applications

The emission inventory and its basic statistics are mainly used for five different purposes:

1. International reporting

2. As a tool for public administration and the authorities

3. Research and education/teaching

4. Market, resource and environmental mapping

5. General information

International reporting is an important use of the official statistics. Figures from the emission inventory are being used by the Ministry of Climate and Environment and the Norwegian Environment Agency in reports to CLRTAP. These figures state whether Norway has reached its targets or not. Also Eurostat, OECD and others are given access to the figures.

The emission inventory is used by the authorities in environmental information documents, such as Regjeringens miljøvernpolitikk og rikets miljøtilstand (The Government's environmental policy and the state of the environment in Norway), which is published every second year, and also in different SDIs: Sustainable Development Indicators.

Statistics Norway also makes use of the emission inventory, both in order to make forecasts/prognoses and as a basis for economic analyses. The project NOREEA (Norwegian Economic and Environmetal Accounts) including NAMEA (National Accounts Matrix including Environmental Accounts) shows the connection between economic and environmental development.

Different public and private institutions use the statistics in studies connected to emission technology, pollution, health and economy.

The emission inventory is an important source of information for newspapers, other news media, environmental organisations and other non-governmental organisations.

Equal treatment of users

No external users have access to the statistics and analyses before they are published and accessible simultaneously for all users on ssb.no at 8 am. Prior to this, a minimum of three months' advance notice is given in the Statistics Release Calendar. This is one of Statistics Norway’s key principles for ensuring that all users are treated equally.

Coherence with other statistics

The statistics are produced in a flexible model format which gives the opportunity to adjust to different national (e.g. sector grouping) and international standards for emission data. Important international standards include Nomenclature for Reporting (NFR) for reporting to the LRTAP convention. At the same time, the statistics form a basis for analyses, both in Statistics Norway and other institutions.

The delimitation of which emissions to be counted as Norwegian, is slightly different in the Gothenburg Protocol than in Statistics Norway’s ordinary emission statistics. The difference regards aviation, where the emission statistics cover all emissions from domestic aviation, while the Gothenburg Protocol cover landing and take-off only, but includes international flights by both Norwegian and foreign companies. The emissions tend to become slightly lower (about 1 per cent for NOx, slightly less difference for the other gases) according to the Gothenburg Protocol than in Statistics Norway’s statistics. All figures in the statistics are according to Statistics Norway’s ordinary emission statistics, except in the text wherever an explicit reference to the Gothenburg Protocol is made.

Legal authority

Not relevant. (No particular data collection.)

EEA reference

Not relevant.



The statistics include emissions from Norwegian territory and present emission surveys for a number of different pollutants:

Acidifying pollutants:

Nitrogen oxides (NO X ), sulphur dioxide (SO 2 ) and ammonia (NH 3 ).

Other pollutants: NMVOC (non-methane volatile organic compounds) and carbon monoxide (CO).

The emission figures are furthermore distributed between emission sources (e.g. process emissions in manufacturing, heating in households) or by industry(e.g. metal production, construction).

Data sources and sampling

 National emissions to air are mainly estimated from existing statistics on activity level and emission factors (emission per unit activity). Emissions from large industrial plants are based on data from the plants' own reports to the Norwegian Environment Agency. No particular measurements or other kinds of special data collection take place in connection with the preparation of national emission statistics. The regional figures are made by breaking down the national figures.

A detailed description of the data sources for the national air emission surveys is presented in Informative Inventory Report, IIR (2017).

Collection of data, editing and estimations

Statistics Norway does only to a small extent collect data specifically for the emission inventory. The goal for data collection for the emissions inventory is that these statistics shall be based on already existing registers and statistics. However, it may be necessary to make some adjustments for this special purpose.

Data reported directly to the Norwegian Environment Agency (emission data from point sources, data from large industrial plants) are quality checked by the Norwegian Environment Agency. In addition, a consistency check is done by Statistics Norway. Statistics Norway is responsible for quality control of the activity data and emission figures from the model. No particular controls are performed on data from Statistics Norway's own primary statistics used in the emission calculations, as it is presupposed that the data already have been quality controlled.

The controls used in connection with the emission calculations can be divided into two parts:

1. Revision/quality control of input data, for example information about emissions per industrial plant from the Norwegian Environment Agency.

2. Revision/quality control of the emission figures (output from the model).

1. Revision/quality control of input data The possibility to check the input data varies, depending on the collection methods and who collects the data. The controls will mainly be:

*To compare data with figures reported from the same unit earlier

*To collect missing data

*To contact industrial plants regarding obvious errors or by asking questions about the reported figures

*Lack of data in time series can be interpolated or filled in by use of estimates. The primary statistics in SSB are submitted to fixed revision routines. There is no additional control of primary data.

2. Revision/quality control of the emission figures (output from the model) The national figures must be controlled source by source, by comparing with figures from previous years or figures for the same year calculated one year ago. Breaks in the series must be explained.

For comparisons between different calculations for the same year, the target is that all changes should be explained as change in data or method. For comparisons between different years, the target is to explain all large changes in the time series.

In the revised version of the model, the main part of the quality control will be to check the input data.

Every third year, there is an international examination (review) of the emission inventory. The examination is a centralised review performed by a group of experts. The Norwegian emission inventory was reviewed in 2013.

The emission inventory is mainly based on calculations. Only a few industrial plants continuously measure their emissions. Some plants have periodic measurements that are scaled up to annual levels. For other plants and other sources than manufacturing industries, the emission figures are calculations, often of the type:

Emission = Activity data * emission factor

Activity data can be for example tonnes of fuel oil used by an industry, while the emission factor expresses the emission of a component in proportion to the activity (for example tonnes of SO 2 /tonne fuel oil). The emission factors are usually based on measured values, national or international.

The estimation methods are described in detail in IIR (2017).

Seasonal adjustment

Not relevant


The general rule for publication is that data cannot be released unless they contain information from at least three or more participants (i.e. industrial enterprises etc). This rule can be waived if permission from the parties involved is granted. Such data can be published if they are already made available for the public elsewhere.

Comparability over time and space

One of the main goals with the emission inventories is to follow the development in the emissions over a period of time. In order to make this possible, recalculations are done for all years to obtain consistent time series when new factors or better methods are taken into account.

International definitions, in addition to guidelines to calculation and reporting of emission data lead to comparable emission inventories in the different countries.

Accuracy and reliability

Sources of error and uncertainty

The emission figures are based on many different data sources. These sources may contain data from different registers or data reported from industrial plants. The model uses factors from various analyses. The results from the model will therefore reflect the uncertainties in the source material and the calculation methods that are used.

The statistics are based both on administrative sources, complete surveys and sample surveys. Calculation of sample variance, skewness or non-response for the emission figures is not relevant.

The statistics are based both on administrative sources, complete surveys and sample surveys. Calculation of sample variance, skewness or non-response for the emission figures is not relevant.

On a national level the pollutants have been ranked according to uncertainty in Informative Inventory Report, IIR (2017) as follows:


In Rypdal and Zhang (2001) , the uncertainties in emissions of long-range air pollutants are quantified.


In December each year the emission statistics published in May is revised. Data back to 1990 is also revised if new information about emission factors, activity data or calculation methodology is available.