The inventory part for mobile sources comprises the emissions from the following transport sectors/machinery types:

• Road transport: Cars, vans, trucks, buses, mopeds and motorcycles
• Military: Military flights and land based activities
• Railways: Rail cars and locomotives
• Domestic navigation: Domestic ferries, ferry boats, pleasure craft, other sea transport between Danish ports, or sea transport between Denmark and Greenland/Faroe Islands
• International navigation: Fuel consumption (statistical sales) by vessels with a foreign destination
• Domestic civil aviation: Flights between Danish airports, or flights between Denmark and Greenland/Faroe Islands
• International civil aviation: International flights from Denmark
• Agriculture/forestry/fisheries: Agricultural and forestry working machinery and fishing vessels
• Industry: Non road working machinery, mainly building and construction
• Residential: Small gasoline working machinery in the residential sector
• Commercial and institutional: Small gasoline working machinery in the commercial and institutional sector

The emission inventory basis for mobile sources is fuel consumption information from the Danish energy statistics. In addition, background data for road transport (fleet and mileage), air traffic (aircraft type, flight numbers, origin and destination airports), navigation (ferry technical data, no. of round trips and sailing time per ferry route) and non-road machinery (engine no., engine size, engine load factor and annual working hours) are used to make the emission estimates sufficiently detailed. Emission factor data mainly comes from the EMEP/EEA Air Pollutant Emission Inventory Guidebook or from specific Danish research studies (e.g. Winther, 2018; Winther and Nielsen, 2006).  

Road transport

Set in relation to the Danish national emission totals, the largest emission shares for road transport are noted for NO_x, CO₂, CO, BC, PM_2.5, PM₁₀, NMVOC and TSP. In 2017 the emission percentages were 28, 32, 27, 14, 8, 7, 7 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 2017 the calculated fuel consumption and emission changes for CO₂, CH₄ and N₂O are 35, 28, -88 and 47 %. The calculated 1985-2017 fuel consumption and emission changes for NO_x, NMVOC, CO, particulates (exhaust only: Size is below PM_2.5) and BC are 53, -66, -89, -88, -81 and -75 %.

The most significant emission changes from 1985 to 2017 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 1381 % (due to the introduction of catalyst cars).   

Figure 1: Emissions from road transport, 2017. Click on the figures to enlarge.

CO₂ emissions are directly fuel consumption dependent and, in this way, the development in the emission reflects the trend in fuel consumption. The impact of the global financial crisis on fuel consumption and associated emissions for road transport becomes visible for 2008 and 2009. In 2017, the road transport fuel consumption share of the CO₂ neutral bio fuels (ethanol and biodiesel), has increased to 4.3 %. The most important CO₂ emission source for road transport is passenger cars, followed by heavy-duty vehicles, light-duty vehicles and 2-wheelers in decreasing order.

An undesirable environmental side effect of the introduction of catalyst cars is the increase in the emissions of NH₃ from the first two generations of catalyst cars (Euro I and II) compared to conventional cars. The emission factors for later catalytic converter technologies are considerably lower than the ones for Euro I and II, thus causing the emissions to decrease from 2001 onwards (Figure 6.28).

Historically, the emission totals of NMVOC and CO have been very dominated by the contributions coming from private cars. However, the NMVOC and CO (and NO_x) emissions from this vehicle type have shown a steady decreasing tendency since the introduction of private catalyst cars in 1990 (EURO I) and the introduction of even more emission-efficient EURO II, III, IV and V private cars (introduced in 1997, 2001, 2006 and 2011, respectively).    

For NO_x the emission decrease for passenger cars is composed of a significant drop in emissions from gasoline cars driven by technology improvements, and an increase in emissions from diesel cars due to the dieselization of the Danish vehicle fleet, and almost unchanged emission factors for diesel passenger cars throughout the period regardless of EU emission legislation demands. For light duty vehicles the NO_x emission trend is also the result of a technology driven emission reduction for gasoline vehicles, and a traffic induced emission increase for diesel vehicles; the emission factors for the latter vehicle category have been relatively constant over the years just as for diesel cars.

For heavy duty vehicles the real traffic emissions are not reduced in the order as intended by the EU emission legislation. Most markedly for Euro II engines, the emission factors are even higher than for Euro I due to the so-called engine cycle-beating effect. Outside the legislative test cycle stationary measurement points, the electronic engine control for heavy duty Euro II and III engines switches to a fuel efficient engine running mode, thus leading to increasing NO_x emissions. However, the reduction in transport activities due to the global financial crisis and improved emission factors causes the NO_x emissions for heavy duty vehicles to decrease significantly in 2008 and 2009.

Exhaust particulate emissions from road transportation vehicles are well below PM_2.5. The emissions from light- and heavy-duty vehicles have significantly decreased since the mid-1990s due to gradually stricter EURO emission standards. In recent years until 2008 the environmental benefit of introducing gradually cleaner diesel private cars has been somewhat outbalanced by an increase in sales of new vehicles. After 2008 the PM emissions gradually become lower due to the increasing number of Euro V cars equipped with particulate filter sold in Denmark from 2006 onwards.

BC - commonly understood as the solid part of the particulate emissions - is calculated as shares of TSP for each Euro engine technology class. In broad terms the development in BC emissions follows the TSP emission trend, but deviates in some cases, most markedly for diesel cars and vans. For these vehicle types the BC share of TSP increases in moderate steps from conventional engine technologies to Euro IV. As a result the BC emission development becomes environmentally less positive than for TSP, until the introduction of Euro V vehicles, for which the installed particulate filters have very high removal rates of BC.

The trend in non-exhaust particulate matter (brake and tyre wear and road abrasion) follows the traffic growth in general. In 2017 the emission share of non exhaust PM_2.5 was 60 % of total road PM_2.5. The non-exhaust particulate emissions are gaining more relative importance, in pace with the year by year reductions of exhaust particulate emissions.    

Figure 2: Time-series for emissions from road transport, 1990-2017. Click the figures to enlarge. 

Other mobile sources

For other mobile sources the emissions of NO_x, CO, BC, CO₂ and SO₂ have the largest shares of the national totals in 2017. The shares are 27, 26, 12, 9 and 7 %, respectively. The 2017 NMVOC, TSP, PM₁₀ and PM_2.5 emission shares are 5, 6, 4 and 1 %, respectively

From 1990 to 2017 the emissions of CO₂ (and fuel use), CH₄, and N₂O have changed by -16, -56 and -4 %. From 1990 to 2017, the calculated emission changes for SO₂, NO_X, NMVOC, CO and PM (all size fractions) are -95, -36, -62, -36, -80 and -81 %, respectively.    

Figure 3: SO₂, NO_X, NMVOC, CO, CO₂, PM and BC emission shares per source category for other mobile sources in 2017. Click the figures to enlarge.

For other mobile sources, the highest CO₂ emissions in 2017 come from Agriculture/forestry/fisheries (1A4c), Navigation (1A3d) and Industry-other (1A2g) with shares of 39, 20 and 18 %, respectively. The 1990-2017 emission trend is directly related to the fuel consumption development in the same time-period. Minor CO₂ emission contributors are sectors such as Commercial/Institutional (1A4a), Residential (1A4b), Railways (1A3c), Civil Aviation (1A3a) and Other (1A5).

For SO₂ the trends in the Navigation (1A3d) emissions mainly follow the development of the heavy fuel oil consumption and the sulphur content of the fuel. The SO₂ emissions for Fisheries (1A4c) correspond with the development in the consumption of marine gas oil. The main explanation for the development of the SO₂ emission curves for Railways (1A3c) and non-road machinery in Agriculture/forestry (1A4c) and Industry (1A2f), are the stepwise sulphur content reductions for diesel used by machinery in these sectors.

In general, the emissions of NO_X, NMVOC, CO, PM_2.5 and BC from diesel-fuelled working equipment and machinery in agriculture, forestry and industry have decreased slightly since the end of the 1990s mainly due to gradually strengthened emission standards given by the EU emission legislation directives. For industry, the emission impact from the global financial crisis becomes very visible for 2009.

The opening of the Great Belt Bridge in 1997 has caused significant reductions of the NO_x and particulate emissions from navigation, due to the closing of several domestic ferry routes. For railways, the gradual shift towards electrification explains the declining trend in diesel fuel consumption and NO_X emissions for this transport sector until 2001. The 1990-2017 PM_2.5 emissions for navigation and fisheries are determined by the fuel use fluctuations in these years, and the development of the emission factors, which to a major extent is a function of the fuel sulphur content. 

For NMVOC and CO, the significant emission increases for the commercial/institutional and residential sectors after 2000 are due to the increased number of gasoline working machines. Improved NMVOC emission factors for diesel machinery in agriculture and gasoline equipment in forestry (chain saws) are the most important explanations for the NMVOC emission decline in the Agriculture/forestry/fisheries sector. This explanation also applies for the industrial sector, which is dominated by diesel-fuelled machinery. From 1997 onwards, the NMVOC emissions from Other decrease due to the gradually phase-out of the 2-stroke engine technology for recreational craft. The main reason for the significant 1985-2006 CO emission decrease for Agriculture/forestry-/fisheries is the phasing out of gasoline tractors.    

Figure 4: Time-series for emissions from other mobile sources, 1990-2017. Click the figures to enlarge. 

Emission factors for mobile sources are available on the emission inventory home-page.

For a more detailed description of the data and methodology for the inventory of mobile sources see the report Danish emission inventories for road transport and other mobile sources and the annexes for the report.