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Transport contribution to air quality

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Assessment made on  01 Nov 2004

Generic metadata


Transport Transport (Primary theme)

Air pollution Air pollution

DPSIR: Impact


Indicator codes
  • TERM 004
Geographical coverage:

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Policy issue:  Meet EU air quality standards set for protection of human health

Key messages

  • Road transport is the largest contributor to NOx emissions in Europe and the second largest for PM. The data analysed from selected stations in major urban 10agglomerations, indicate that both mean and maximum values of NO2 concentrations at road traffic stations appear to remain relatively stable (trend is smaller than the statistical uncertainty on estimate) during the period 1999-2002 and are accompanied by a similar tendency in the background concentrations. For PM the situation appears 10more complex, since although mean and maximum values at road traffic and background stations appear to remain relatively stable during the period 1999-2001, both mean and maximum values at both station types show a large increase in 2002. This is particularly due to the large increase in the concentrations measured in Krakow and Prague, although an increase is also observed in other cities across Europe. Overall the decrease in emissions does not appear to have a statistically significant influence on the air quality and the increase in the number of vehicles is off-setting the technological and fuel quality improvements.


Key assessment


NOx emissions from road transport decreased by 33% in EEA31, EU9 and EU15 and 21% CC4 countries between 1990 and 2002 (see table 6). This was mainly due to the introduction of catalysers on new cars. Increasing road travel and increasing number of vehicles (see TERM 2004 32, EEA 2003) has partly offset reductions achieved by emission abatement. Even though emissions have decreased, in 2002 road transport still contributed 40% to the total emissions in EEA31 countries, 37% in EU9 countries, 44% in EU15 and 25% in CC4 countries (see table 7). The difference between average yearly traffic and background concentrations (see fig. 3) varies greatly from city to city, but overall higher values are observed at the traffic stations, indicating that traffic contributes significantly to NO2 concentrations in urban areas. Higher traffic concentrations are systematically not observed for the city of Athens, leading to the conclusion that perhaps significant sources, other than traffic, are also present. It could also be the case that the location of the station is such that traffic significantly influences the concentrations measured at the background station, in which case other stations should be chosen, but this could not be realised as data availability was limited. Overall, the interannual variation of the difference between traffic and background values shows a decreasing tendency, mainly due to an increase in the traffic values (see fig. 3 and table 2).


Primary and secondary emissions of PM decreased by 33% in EEA31, 36% in EU9, 34% in EU15 10and 20% in CC4 countries between 1990 and 2002 (see table 6). The emission reductions were mainly due to abatement measures including fuel switching and the increased penetration of catalytic converters, since the application of abatement techniques to reduce precursor emissions often reduces the primary particle emissions also. However, road transport still contributes significantly to total primary and secondary emissions in 2002, 23% in EEA31, 16% in EU9, 27% in EU15 and 12% CC4 countries (see table 7) and the overall increase in road travel and number of vehicles (see TERM 2004 32, EEA 2003) has partly offset reductions achieved by emission abatement.


Road transport emissions of sulphur dioxide have been reduced by 76% between 1990 and 2002 in EEA31, 73% in EU9, 88% in EU15 and 11% in CC4 countries (see table 6). The emission reductions were mainly due to the considerable reductions in the sulphur content of automotive fuels over the period, which appears to have had an effect on the concentrations observed, despite the increasing traffic volumes (see TERM 2004 32, EEA 2003). However, in 2002 SO emissions from road transport 2 only represent 2% of the total emissions in all EEA31 countries (see table 7).


O3 concentrations across Europe depend on ozone precursor emissions, however the relationship is highly non-linear. Emissions of TOFP have been reduced between 1990 and 2002 by 43% in EEA31, 27% in EU9, 48% in EU15 and 16% in CC4 countries (see table 6), but transport volumes have increased partly off-setting the effect of the emission reductions (see TERM 2004 32, EEA 2003).


Although in 2002 road transport contributes significantly to total emissions, 43% in EEA31, 31% in EU9, 49% in EU15 and 29% in CC4 countries (see table 6), CO traffic and background concentrations showed very low values compared to the limit value (running 8-hour average concentration of 10mg/m3 in 2005), hence it was not considered necessary to include this pollutant in the analysis. Moreover, a further reduction in CO emissions is expected, judging from the trend between 1990 and 2002 where a reduction of 53% in EEA31 was observed. However this reduction was less in CC4 countries (17%) but concentration data for these countries were not available in AirBase.

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