Transport

 Transport is a major source of greenhouse gases and air pollutants. Despite the improving efficiency of engines over the last decade, road transport in particular, is a major source of emissions of carbon dioxide (CO₂), nitrogen oxides (NO_x), carbon monoxide (CO), particulate matter (PM) and copper.

The overall increase in demand for passenger and freight transport, insufficient compliance and control of specified emission standards in the past, led to the non-compliance of assumptions towards the goal of reducing emissions. A good example are the average NO_x emissions from diesel engines of the EURO 5 emission standard when tested in traffic. Emissions were at the same level as previous technologies set by older emission standards, and in some cases even exceeding the limits set by standards before the Euro standards. Thus, these emissions did not decrease as assumed, which means that the reduction was not as high as expected.

Total greenhouse gas emissions from the transport sector in the last year (2021) accounted for 18% of all greenhouse gas emissions in Slovakia, which is 7 523 Gg CO₂  eq. The increase in these emissions compared to the base reference year 1990 is more than 10% and copmpared to the covid year 2020 7% increase due increase of transport intensity. Road transport has the largest share on transport sector - almost 97%.

NO_x emissions are mainly produced by the combustion of diesel oil. In 2021, it was 19.7 Gg, which is about 34% of all nitrogen oxide emissions in Slovakia. Despite this high values, Slovakia has managed to reduce these emissions by 60% compared to 2005, while the reduction compared to 1990 is 64%. This reduction is mainly due to the improvement of engine technologies and the partial electrification of rail transport. These emission reductions were slowed down by a fraud known as the "dieselgate". As part of this fraud, the on-board computer of certain vehicles was supposed to temporarily reduce the emissions produced by the engine by changing the engine settings in order to meet the emission limits (mentioned above) during periodical tests.

To a lesser extent, transport is responsible also for emissions of other air pollutants such as carbon monoxide (CO) and particulated matter, especially 2.5 micrometres particles (PM_2,5). Their current share in total emissions in Slovakia is about 6% for PM_2,5 and 5% for CO, in the case of carbon monoxide it has significantly decreased compared to 2005 (92%). In the case of PM_2.5, this decrease is "only" 63%. In absolute values, it is 14.2 Gg for carbon monoxide and 1.1 Gg for particulate matter. Behind the significant reduction in carbon monoxide emissions is again increased efficiency of fuel combustion in vehicle engines. Particulated matter emissions are difficult to reduce, as they are mainly produced by tyre, road and brakewear abrasion. The brake systems are also responsible for high copper emisisons. Emissions of copper particles from the brake system are approximately 7 tonnes, annually. The production of particulated matter and copper is thus significantly affected by driving style.

Trends in emissions by individual types of fuels

Trends in emissions of greenhouse gases and pollutants from the transport sector by individual types of fuels have been balanced since 1990. More information on emissions trends from the road transport sector - combustion by types of fossil fuels in Slovakia.

Combustion of diesel (70%), petrol (20%) and natural gas (2%) and, in terms of pollutants, biofuels (6.3%) have the largest share in emissions. Aviation fuels and LPG together account for about 1.7% of transport fuel consumption. A significant share of diesel is due to its use in several modes of transport, such as road, rail and shipping. The share of biomass-based fuels is increasing every year, which is due to the obligation to mix biofuels into fuels used in road and rail transport.