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 two 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 two 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 residential 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, 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, 2008; Winther and Nielsen, 2006).

Road transport

Set in relation to the Danish national emission totals in 2009, the road transport emission shares for NO_x, CO, CO₂, NMVOC, particulates (exhaust PM_2.5: Size is below PM_2.5) and SO₂ were 35 %, 28 %, 25 %, 14%, 6 % and 0.5 %, respectively. For transport as a whole, comprising road transport, railways, domestic civil aviation and domestic navigation, the share of the Danish national total emissions for NO_x, CO, CO₂, NMVOC, SO₂ and particulates (exhaust PM_2.5) were 45 %, 30 %, 27 %, 16 %, 12 % and 8 %, respectively.

From 1990 to 2009 the calculated emission changes for road transport NO_x, CO, CO₂, NMVOC, particulates (exhaust PM_2.5: Size is below PM_2.5) and SO₂ were -42 %, -70 %, +31 %, -78 %, -69 % and -99 %, respectively.

Figure 1: Emissions from road transport, 2009. 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. The most important emission source for road transport is passenger cars, followed by heavy-duty vehicles, light-duty vehicles and 2-wheelers in decreasing order. For SO₂ the emission drop is 99 % (due to reduced sulphur content in the diesel fuel).

Historically, the emission totals of NMVOC and CO have been very dominated by the contributions coming from private cars, as shown in Figures 2d-e. 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 and IV private cars (introduced in 1997, 2001 and 2006, respectively).

In the case of NO_x, the real traffic emissions for heavy duty vehicles do not follow the reductions as intended by the EU emission legislation. This is 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 (Figure 2c). However, the reduction in transport activities due to the global financial crisis 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. The environmental benefit of introducing diesel private cars with lower particulate emissions since 1990 is more than outbalanced by an increase in sales of new vehicles in recent years (Figure 2e).

The trend in non-exhaust particulate matter (brake and tyre wear and road abrasion) follows the traffic growth in general, and in 2009 the non exhaust PM_2.5 emissions were 56 % compared to total road exhaust 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, 1990-2009. Click on the figures to enlarge.

 a) b) 

c) d) 

e) f)

Other mobile sources

Set in relation to the Danish national emission totals in 2009, the emission shares for other mobile sources for NO_x, CO, CO₂, NMVOC, PM_2.5 and SO₂ were 32 %, 33 %, 8 %, 13 % , 9 % and 14 %, respectively.

From 1990 to 2009 the calculated NO_x, CO, CO₂, NMVOC, PM_2.5 and SO₂ emission changes were -22 %, +8 %, -6 %, -11 %, -61 % and -88 %, respectively.

For other mobile sources, the highest CO₂ emissions in 2009 come from Agriculture/forestry/fisheries (1A4c), Industry-other (1A2f) and Navigation (1A3d), with shares of 45, 20 and 15 %, respectively. The 1990-2009 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 Military (1A5).

Figure 3: Emissions from other mobile sources, 2009. Click on the figures to enlarge.

For SO₂ the trends in the Navigation (1A3d) emissions shown in Figure 4a mainly follow the development of the heavy fuel 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 and PM_2.5 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 1990-2009 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 Navigation decrease due to the gradually phase-out of the 2-stroke engine technology for recreational craft. The main reason for the significant 1990-2006 CO emission decrease for Agriculture/forestry-/fisheries is the phasing out of gasoline tractors.

Figure 4: Time-series for emissions from other mobile sources, 1990-2009. Click on the figures to enlarge.

 a) b) 

c) d)

e)

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.