Aarhus Universitets segl

No. 411: Danish emission inventories for road transport and other mobile sources

Winther, M. 2020: Danish emission inventories for road transport and other mobile sources. Inventories until the year 2018. Aarhus University, DCE – Danish Centre for Environment and Energy, 132pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 411. http://dce2.au.dk/pub/SR411.pdf 


This report explains the emission inventories for road transport and other mobile sources, which are part of the annual Danish emission inventories reported to the UNFCCC (United Nations Framework Convention on Climate Change) and the UNECE LRTAP (United Nations Economic Commission for Europe Long Range Transboundary Pollution) convention. The sub-sectors for other mobile sources (Table 0.1) are military, railways, inland waterways, national sea traffic, national fishing, civil aviation and non-road machinery used in agriculture, forestry, industry, household/gardening and commercial/institutional.

The emissions of CO2 (carbon dioxide), CH4 (methane) and N2O (nitrous oxide), SO2 (sulphur dioxide), NOx (nitrogen oxides), NMVOC (non-methane volatile organic compounds), CO (carbon monoxide), NH3 (ammonia), PM (particulate matter), BC (black carbon), heavy metals, dioxins, HCB (hexachlororbenzene), PCBs (polychlorinated biphenyls) and PAHs (polycyclic aromatic hydrocarbons) are shown in time-series as required by the UNFCCC and the UNECE LRTAP conventions, and grouped according to the UNFCCC Common Reporting Format (CRF) and UNECE National Format for Reporting (NFR) classification codes.


The emission calculations for road transport are made with an internal DCE model, with a structure similar to the European COPERT 5 (COmputer Programme to calculate the Emissions from Road Transport) methodology. The emissions are calculated for operationally hot engines, during cold start and fuel evaporation. The model also includes the emission effect of catalyst wear. Input data for vehicle stock and mileage is obtained from DTU Transport, and is grouped according to average fuel consumption and emission behaviour. The emissions are estimated by combining vehicle and annual mileage numbers with emission factors for hot engines, emission ratios between cold and hot engines and factors for gasoline evaporation.

The emissions from air traffic are also calculated with a DCE model. For 2001-2018, the emission estimates are made for each flight, using flight data from the Danish Transport Authority and landing/take off (LTO) and distance related emission factors from the EMEP/EEA guidebook. For previous years, the background data consist of LTO/aircraft type statistics from Copenhagen Airport and total LTO numbers from the Danish Transport Authority. By using appropriate assumptions, a consistent time-series of emissions is produced back to 1985 using also the detailed city-pair emission inventory results from 2001 as a basis.

National sea transport is split into regional ferries, small ferries (island and short cut ferries), freight transport between Denmark and Greenland/Faroe Islands, and other national sea transport. For ferries, the fuel consumption and emissions are calculated as a product of number of round trips, sailing time per round trip, engine size, engine load factor and fuel consumption/emission factor. For freight transport between Denmark and Greenland/Faroe Islands, and other national sea transport, the calculations are simply fuel based using fuel sale figures in combination with average fuel related emission factors.

Non-road working machines and equipment are grouped in the following sectors: Agriculture, Forestry, Industry, Household/Gardening and Commercial/Institutional. Recreational craft are grouped in the sector Other. In general, the emissions are calculated by combining information on the number of different machine types and their respective load factors, engine sizes, annual working hours and emission factors.

For military, railways and fishery activities the emissions are calculated as the product of fuel use and emission factors.

Fuel sales data are obtained from the Danish energy statistics provided by the Danish Energy Agency (DEA). For road transport and aviation, the emission results are adjusted in a fuel balance to ensure that all statistical fuel sold is accounted for in the calculations. For national sea transport, the fuel consumption of heavy oil and gas oil for ferries is calculated directly by DCE. The difference between fuel sales statistics for national sea transport and bottom up fuel estimates for ferries is allocated to other national sea transport. In order to comply with the IPCC guidelines the fuel consumption by vessels between Denmark and Greenland/Faroe Islands are subtracted from the DEA fuel sales figures for international sea transport, and added to the national part of the emission inventories.

Emissions from road transport

Set in relation to the Danish national emission totals, the largest emission shares for road transport are noted for CO2, NOx, CO, BC, PM2.5, PM10, NMVOC and TSP. In 2018, the emission percentages were 30, 27, 25, 19, 9, 8, 5 and 4 %, respectively. The emissions of NH3, N2O, CH4 and SO2 have marginal shares of 1.2, 2.4, 0.1 and 0.8 %, respectively.

From 1990 to 2018, the calculated fuel consumption and emission changes for CO2, CH4 and N2O are 38, 32, -88 and 51 %. The calculated 1985-2018 fuel consumption and emission changes for NOx, NMVOC, CO, particulates (exhaust only: Size is below PM2.5) and BC are 56, -68, -90, -89, -84 and -79 %.

The most significant emission changes from 1985 to 2018 occur for SO2 and NH3. For SO2 the emission drop is 99 % (due to reduced sulphur content in the diesel fuel), whereas the NH3 emissions increase by 1302 % (due to the introduction of cars with catalysts).

In 2018, the most important CO2 emission source for road transport is passenger cars (55 %), followed by heavy-duty vehicles (31 %), light-duty vehicles (14 %) and 2-wheelers (0 %). For CH4 the 2018 emission shares were 61, 21, 16 and 2 % for passenger cars, 2-wheelers, heavy-duty vehicles and light-duty vehicles, respectively, and for N2O the emission shares for passenger cars, heavy and light-duty vehicles were 53, 36 and 11 %, respectively.

For 2018, the following emission shares for passenger cars, heavy-duty vehicles, light-duty vehicles and 2-wheelers (percentage shares in brackets) are calculated for NOx (47, 25, 27 and 1 %), NMVOC (55, 4, 4 and 16 %), CO (80, 5, 4 and 11 %), PM (45, 23, 29 and 3 %), BC (43, 22, 34 and 1 %), and NH3 (90, 5, 5 and 0 %).

Set in relation to total road transport emissions in 2018, the emission shares of TSP, PM10, PM2.5 and BC were 84, 77, 65 and 24 %, respectively, related to tire, brake and road abrasion.

Emissions from other mobile sources

For other mobile sources, the emissions of CO, NOx, CO2 and SO2 have the largest shares of the national totals in 2018. The shares are 25, 24, 15, 8 and 6 %, respectively. The 2018 NMVOC, TSP, PM10 and PM2.5 emission shares are 4, 1, 4 and 6 %, respectively, whereas the emissions of N2O, NH3 and CH4 have marginal shares of around 1 % or less in 2018.

From 1990 to 2018 the calculated emission changes for CO2 (and fuel use), CH4 and N2O are -19, -59 and -7 %, respectively. The emissions of SO2, NOX, NMVOC, CO and PM (all size fractions) have changed by -96, -43, -64, -38, ‑82 and -83 %, respectively, from 1985 to 2018. For NH3 the emissions increased by 14 % in the same time period.

The largest source of NOx emissions is national navigation, followed by agriculture/forestry, fisheries and industry. For CO2, particulates (all size fractions) and BC the largest emission sources are agriculture/forestry, industry and national navigation, in this consecutive order. For NMVOC and CO most of the emissions come from gasoline fuelled working machinery in the commercial/institutional, agriculture/forestry and residential sectors.

Heavy metals

Heavy metal emissions are calculated for fuel and engine oil as well as for tyre, brake and road wear. The road transport shares for copper (Cu), lead (Pb), zinc (Zn), chromium (Cr) and cadmium (Cd) are 96, 46, 45, 11 and 6 % of national totals in 2018. For other mobile sources, the nickel (Ni), arsenic (As) and selenium (Se) shares are 39, 11 and 10 %. For the remaining components, the emission shares are less than 7 %.

The most important exhaust related emissions (fuel and engine oil) for road transport (percent of national total in brackets) are Zn (13 %), Cd (5.5 %), Cr (6.1 %) and Hg (7.5 %). The most important wear related emissions are Cu (96 %) and Pb (44 %) almost solely coming from tyre wear, and Zn (31 %) from brake and tyre wear. For other mobile sources, the emissions of Ni and As arise from the use of marine diesel oil and residual oil in fisheries and navigation. The emissions of Pb almost solely come from the use of aviation gasoline.

In general, the development in emissions follows the trends in fuel/engine oil consumption and vehicle mileage (wear related emissions). It must be noted, however, that there has been an almost 100 % decline in the exhaust related emissions of Pb, due to the phasing out of leaded gasoline fuels until 1994.


Dioxins, HCB, PCBs and PAHs are categorized as POPs (persistent organic pollutants). For the individual POP components, the emission shares for road transport and other mobile sources are 5 % or less of the national total in 2018.


For mobile sources in 2018, the CO2 emissions are determined with the highest accuracy (5 % uncertainty), followed by the emissions of CH4 (30 %), TSP (45 %), SO2 (46 %), PM10 (47 %), PM2.5 (51 %), NMVOC (52 %), BC (53 %), NOx (55 %), CO (57 %) and N2O (113 %).

The uncertainties for the 1990-2018 emission trends listed by emission component (percentage uncertainty in brackets) are: CO2 (5 %), CH4 (2 %), TSP (11 %), SO2 (1 %), PM10 (7 %), PM2.5 (4 %), NMVOC (4 %), BC (2 %), NOx (8 %), CO (9 %) and N2O (59 %).

For NH3, heavy metals and PAHs the 2018 emissions have uncertainty levels of between 700 and 1000 %. In this case, the emission trend uncertainties are significantly lower; still large fluctuations exist between the calculated values for the different emission components.