Older petrol and diesel vehicles are responsible for a disproportionate share of fine particulate matter (PM2.5 and PM10) emissions in Finland, a new study has found, raising concerns about air quality and the ageing vehicle fleet, according to the University of Eastern Finland.

The research shows that around 50% of traffic-related particle emissions are generated by a small fraction of internal combustion engine (ICE) vehicles, about 10%, most of which are more than 15 years old. The findings highlight how emissions are unevenly distributed across the vehicle population, with older models contributing far more pollution than newer cars.

A Small Number of Vehicles Emit Most of the Harmful Emissions

One of the key findings of the study carried out in late 2025 is that 10% of internal combustion engine (ICE) vehicles emit approximately half of all particle emissions during highway driving and 5% of vehicles emit the same level of emissions when idling during periodic technical inspections (PTI).

The researchers found that the worst offenders for vehicle particles are older diesel vehicles that do not have a diesel particulate filter. With one of the oldest passenger vehicle fleets in Europe, Finland has a particularly high level of particle emissions from the ICE passenger vehicle fleet, and this may explain why particle emissions have not improved more quickly, despite advances in ICE vehicle emission standards.

The research data indicate that new-generation ICE vehicles emit approximately 70% fewer particles than older model ICE vehicles under typical highway driving conditions. This points to targeting the highest-emitting vehicles as a quicker way to improve air quality than broad-based measures applied to all passenger vehicles.

Diesel Cars Produce More Particles Than Petrol Cars

Statistical analysis of the research indicates that vehicle type and size will significantly influence particle output from an internal combustion engine (ICE). Significant differences exist between petrol and diesel-powered vehicles in terms of particle emissions.

Diesel-powered cars built after 2011 with diesel particulate filters produce significantly less particulate matter than older diesel vehicles without DPFs. By contrast, older petrol-powered cars, particularly pre-Euro 6 or direct-injection models, continue to produce similar amounts of particulate matter as vehicles built in 2000. The data indicate that Euro 5 and Euro 6 petrol vehicles emit more particulate matter at idle than some newer models, but generally less than older diesel vehicles with no DPF.

Emissions from ICE-powered petrol-fueled vehicles are nearly as high as those emitted from ICE-powered diesel-fueled vehicles; thus, ICE-powered vehicles are adversely affecting the quality of our environment, given that there has been no substantial reduction in their emission of particulate matter over time.

Air Quality and Policy: Impacts of Air Pollution 

Air quality has been greatly affected due to fine particulate emissions from traffic, particularly in metropolitan or urban areas. The authors of this research concluded that air quality can be significantly enhanced if policies are implemented to remove and/or replace the vehicles with the worst emissions.

In addition, the results of this study illustrate what will happen as a result of the new scrappage premium introduced in Finland in early 2026 to encourage people to get rid of cars that are at least ten years old. The researchers anticipate that this new incentive will help accelerate the transition to lower-emission vehicles and decrease overall particulate matter emissions.

Researchers expect that as older gasoline-powered vehicles are replaced with electric vehicles, emissions produced by vehicles will decline. However, it should be noted that other sources of emissions, such as brake wear, tyre wear and road surface wear,will continue to increase in emissions, thereby necessitating attention.

The study findings are based on hundreds of vehicle inspections and real-world measurements of vehicles on Finnish roads, allowing a comprehensive evaluation of emission patterns across Finland’s passenger vehicle fleet.