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Specific emissions of air pollutants

Indicator Fact Sheet (Deprecated)
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Assessment made on  01 Sep 2005

Generic metadata


Transport Transport (Primary theme)

DPSIR: Driving force


Indicator codes
  • TERM 028
Geographic coverage:

Policy issue:  Reduce emissions per passenger-km and per tonne-km.

Key messages

  • The specific emissions of air pollutants from passenger and freight transport decreased during the time period 1990 - 2004 for the majority of transport modes and especially for passenger transport. The highest reduction of specific emissions can be observed in the road sector, following the implementation of increasingly stricter emission standards. Railway emissions from freight transport decreased slightly over the past fourteen years. However, railway emissions produced from passenger transport remained approximately constant during this time period. Inland waterway freight transport stabilised its emissions per tonne-kilometre, while maritime passenger and freight transport even increased their specific emissions during the time period considered. Rail and water transport are still relatively clean forms of transport - compared to road and air transport - but without any regulations on their emissions, these modes might lose this leading position.


Key assessment

Road remains by far the most polluting passenger transport mode with respect to CO and VOC specific emissions, even though it recorded the highest decreases (55 and 70 % for CO and VOC emissions respectively) from 1990 to 2004 compared to the other modes. As regards NOx specific emissions, road passenger transport emits about the same as air and rail transport and less than half of the specific emissions from maritime transport. Road is also the most polluting freight transport mode for all pollutants. However, specific emissions decrease by up to 40 % (in the case of CO emissions) from 1990 to 2004.

Rail is the cleanest mode of transport for all pollutants considered above. Specific emissions of rail passenger transport remain approximately constant from 1990 to 2004, while there was a decrease of up to 20 % in the rail freight transport over the same period. Specific emissions from trains depend critically on the technical level and the method of energy production used. The trend is towards electric powered trains for the future, especially for passenger traffic. This indicates that the focus in the future should be in controlling emissions from power generation, along with implementing the engine economy and emission control technology, which has already advanced.

Following rail, maritime shipping is the second cleanest mode of freight transport, except for specific sulphur oxide (SOx) emissions, which is the highest for shipping (and aviation), mainly due to the high sulphur content of bunker fuels. However, maritime shipping remains the most polluting passenger transport mode with regard to the specific NOx and PM emissions. The emissions generated by the maritime fleet are largely dependent on the quantity of fuel consumed; however, there are several factors besides fuel consumption, which influence the emissions generated. These include the fuel quality and the engine type. In particular, SOx and PM emissions are influenced by the quantity of sulphur within the fuel. In the future, emission reductions are expected from waterborne transport, mainly as a result of improved fuel quality and engine technology. EU legislation setting more stringent limits for sulphur content in fuel oils will greatly contribute to the expected emission reductions. To this end, the European Commission proposed "A European Union strategy to reduce atmospheric emissions from seagoing ships" (European Commission, 2002).

It should be noted that the significant reductions in the emissions of all pollutants from road transport are mainly attributed to technological improvements and policy measures resulting from the strict emission standards imposed. On the other hand, the emissions from the other modes of transport are not subject to any emission control regulations, which would result in emission reductions similar to those from road transport.

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