Transport emissions – Historic evolution and outlook [ Article 2009100604 - 06/10/2009]

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Transport is a major source of greenhouse gas and air pollutant emissions and plays an important role in their evolution. Transport emissions are closely monitored and their future evolution is integrated into the FPB transport model, PLANET. The publication uses a decomposition analysis to compare the projected evolution of the emissions in the base scenario of the PLANET model to the base scenario of two other models and to put these in a historic perspective. The analysis focuses on Tank-to-Wheel emissions and is limited to three modes: road transport, railways and inland navigation.

The two other studied models are the PRIMES model and the TREMOVE model. The latter was specifically conceived for the analysis of the impact of transport and environmental measures on transport emissions. The historic evolution of transport emissions is based on the emission inventories drawn up in the framework of international treaties.

In 2007, transport emitted 27% more greenhouse gases than in 1990. Transport was responsible for 19% of the greenhouse gas emissions in Belgium. While total CO2 emissions in Belgium decreased by 8% between 1990 and 2007, emissions by transport increased by 26%. Over the 2005-2030 period, the growth of CO2 emissions should slow down. The scenarios give a different evolution of CO2 emissions that should range between a decrease of 2% and an increase of 18%. These differences can be explained by different assumptions on transport demand growth, the evolution of average fuel consumption by cars and the share of biofuels.

Gasoline cars are the main source of transport emissions of NMVOC and CO. Emissions of these air pollutants more than halved between 1990 and 2007. The decline of NMVOC and CO transport emissions is the combined effect of the growing share of diesel cars and more stringent emissions standards. In 2007, transport was responsible for a quarter of NMVOC emissions and a third of CO emissions in Belgium. The scenarios project a growing share of diesel in road transport and a progressive decrease in emission factors for road vehicles. CO and NMVOC emissions should decrease respectively by 40-75% and 50-70%. The magnitude of the reductions mainly depends on the assumed evolution of emission factors for cars and trucks.

Thanks to stricter emission standards, NOx emissions by transport decreased by a third between 1990 and 2007. In 2007, transport accounted for half the emissions in Belgium. The scenarios predict a further decrease in emissions of 40-56% over the period 2005-2030. The projected reductions depend not only on the assumed reduction in emission factors but also on the projected transport growth.

Transport emissions of particle matter (PM) fell by 19% between 2000 and 2007 and were reduced less than the total emissions in Belgium. The scenarios project a further decline in PM emissions of 63-71%. The differences can be explained by different assumptions on the evolution of the emission factors.

The successive reductions of the maximum sulfur content of road fuels forced SO2 emissions down by 86% between 1990 and 2007. In 2007, transport was responsible for 1% of the total emissions in Belgium. In the future, emissions should continue to fall. The projected reductions vary between 27 and 79%, depending on the assumptions for the sulfur content of fuels.

The decomposition analysis of the main factors influencing future transport emissions proved to be a powerful tool for explaining the differences between the base scenarios.