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With the introduction of targeted policies and measures in recent decades, the emission of most air pollutants from transport in the EU-27 has decreased. Reductions in the road transport sector account for the greatest share of this progress, while emissions from shipping and aviation increased for some pollutants. The dramatic reduction in transport volumes linked to the COVID-19 pandemic led to significant but only temporary reductions in emissions, and an upturn in pollution from transportation is already visible for 2021 and 2022 alongside the rebound of transport volumes.
Figure 1. Emissions of pollutants from transport in EU-27
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Pollutants emitted by transport activities contribute to ambient air pollution and put significant pressure on the environment and human health in Europe. In recent decades, significant policy efforts have addressed transport-related air pollution from various transport modes (road transport, rail, aviation, maritime) and have led to some notable improvements.
Together, such policies have delivered progress in reducing the emissions of many pollutants from the transport sector. Between 1990 and 2022, emissions of nitrogen oxides (NOx) from transport across the EU-27 decreased by 51%, sulphur oxides (expressed as SO2) by 82%, carbon monoxide (CO) by 90%, methane (CH4) and non-methane volatile organic compounds (NMVOCs) by 76% and 91% respectively. In the same time frame, transport emissions of particulate matter (including non-exhaust emissions) with particle diameter of 10µm/2.5µm or less (PM10/2.5) decreased by 46%/58%, respectively.
The onset of the COVID-19 pandemic had an influence on these figures, due to the significant reduction in transport volumes during 2020. However, many of the pollutant levels have rebounded.
At the same time, two air pollutants have demonstrated substantial growth in recent decades. Between 1990 and 2022, transport emissions of ammonia (NH3) increased by 121% (138% in 1990-2019) while nitrous oxide (N2O) increased by 35%. Although transport contributions of NH3 emissions are limited compared to other sectors such as agriculture, their impact on air quality, especially within cities, is reported to be very high. While a powerful greenhouse gas, N2O is also currently considered a dominant ozone depleting substance .
Although most pollutant emissions declined since 1990, the situation is uneven across transport modes. This in part reflects differences in the stringencies of emissions standards.
Road transport has significantly reduced its pollutant emissions since 1990, with the exception of compounds NH3 and N2O. Their recent increase is mainly due to new catalytic systems for the reduction of NOx in diesel engines and the use of enriched fuel mixtures to control NOx at high load in petrol engines . While a significant reduction can be seen for both PM10 and PM2.5, the non-exhaust fraction of these emissions (i.e. from brake and tyre wear or road abrasion) is increasing in percentage and constituted 75% and 59% of PM10 and PM2.5 emissions from road transport in 2022. Non-exhaust emissions will become even more relevant with the progressive decarbonisation of the sector and increases in vehicles mass due to batteries.
Figure 2. Variations (1990-2022) in the emissions of pollutants from transport by mode in EU-27
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Emissions from the aviation sector (i.e. including domestic and international), increased for most pollutants, with the exception of CH4, CO, NMVOC, rebounding after the significant contraction in traffic volumes that occurred during the COVID-19 pandemic. Increases in emissions since 1990 ranged between 47% and 117%, depending on the compound considered.
Differences exist between domestic and international aviation trends for some pollutants (Figure 2). This can be partially explained by the difference in demand evolution and the technology used in domestic and international aviation. The aviation sector's reduction of air pollutant emissions is mainly done at engine design level since the application of advanced aftertreatment systems (as mentioned above) is technologically very challenging.
Maritime sector emissions from domestic navigation decreased during 1990-2022, for all pollutants considered (excluding CH4, which increased by 7%). These reductions range between 88.7% and 0.3%, depending on the compound considered. Conversely, in international navigation most pollutants have increased, aside from PM10, PM2.5 and SO2. This increase in emissions ranged between 5% and 58%, depending on the compound considered. In the maritime sector, many of the pollution reduction technologies already developed in the road sector could in principle be adapted to marine diesel engines. This would yield a significant reduction in air pollutants emissions from the sector with clear environmental benefits.