Emissions of air pollutants have decreased, except for NH3 and N2O, in the EU-27 in recent decades, because of policy efforts across several transport modes. Reductions in the road transport sector account for the greatest share of this progress, while emissions from the shipping and aviation sectors increased with some pollutants. The dramatic reduction in transport volumes linked to the onset of COVID-19 pandemic led to significant reductions in emissions for the year 2020, but this effect is likely to be temporary.

Pollutants emitted by the transport sector put significant pressures on the environment, air quality in particular, in many parts of Europe. Significant policy efforts, although with differences across modes, have addressed transport-related air pollution in recent decades and have led to some notable improvements. For instance, the Ambient Air Quality Directives set limits or target values for concentrations of pollutants in the ambient air, while the NEC Directive sets emission reduction commitments on total national emissions for five air pollutants (NOx, SO2, NMVOC, NH3 and PM2.5). Recently, the European Commission has proposed a revision of the Ambient Air Quality Directives, to closely align air quality standards with World Health Organization guidelines, while putting the EU on a trajectory to achieve zero air pollution by 2050. Emissions from the transport sector are further regulated by vehicle emissions standardsand fuel quality requirements . Local and regional air quality management plans — including initiatives such as low-emission zones— and congestion charges in cities are also in place in many areas. SOx and NOx emissions from international shipping are regulated by Annex VI to MARPOL Convention of the International Maritime Organisation. SOx requirements are transposed in EU law by the Directive on sulphur content in certain liquid fuels including marine fuels.

Together, such policies have delivered progress in reducing the emissions of many pollutants from the transport sector. Between 1990 and 2020, across EU-27, emissions of nitrogen oxides (NOx) from transport decreased by 53%, sulphur oxides (SOx) by 77%, carbon monoxide (CO) by 89%, methane (CH4) and non-methane volatile organic compounds (NMVOCs) by 76% and 90% respectively. At the same time, between 2000 and 2020, EU-27 transport emissions of particulate matter (including non-exhaust emissions) with particle diameter of 10µm/2.5µm or less (PM10/2.5) decreased by 49%/55% respectively. The onset of the COVID-19 pandemic had an influence on these figures, due to the significant contraction in transport volumes during 2020. Indeed, the same reductions between 2000 and 2019 were considerably lower for some pollutants: 41% for NOx, 59% for SOx, 86% for CO, 74% for CH4, 88% for NMVOCs, 39% for PM10, 47% for PM2.5.

Between 1990 and 2020, across EU-27, transport emissions of ammonia (NH3) increased by 99% (139% in 1990-2019) while nitrous oxide (N2O) increased by 16% (38% in 1990-2019). Although transport contributions of NH3 emissions are limited compared to other sectors, their impact on air quality, especially within cities, is reported to be very high . N2O, while a powerful greenhouse gas, is also currently considered a dominant ozone depleting substance.

Although most pollutant emissions declined since 1990, the situation is heterogeneous across transport modes. This in part reflects differences in the stringencies of emissions standards.

Road transport has significantly reduced its pollutants emissions, with the exception of compounds NH3 and N2O. Their recent increase is mostly due to new catalytic systems for the reduction of NOx . For PM, reductions are smaller, due to an increase in non-exhaust emissions like brakes and tyre abrasion. These will become more relevant with the decarbonisation of the sector and increase in vehicle mass due to batteries.

The reduction of pollutant emissions seen in aviation in 2020 is mostly due to the pandemic. Indeed, if calculated for 1990-2019, none of the pollutants reported decreased for international aviation. Only CO and NMVOCs would have shown a large reduction (>20%) in domestic aviation.

Similar considerations hold for shipping, especially international shipping. CO, NOx, NMVOCs, SOx, PM10 and PM2.5 were all between 12% to 30% higher in 2019 than 1990 levels. In the domestic shipping, SOx, NH3 and N2O were between 12% to 16% higher in 2019.