Study shows older petrol and diesel vehicles produce 50% of harmful particle emissions in Finland
In Finland, the average age of passenger cars is among the highest in Europe, and the majority of traffic‑related particle emissions are produced by ICE vehicles that are more than 15 years old. The worst polluters are old diesel cars without a diesel particulate filter.
The study, completed in late 2025, shows that particle emissions are unevenly distributed in Finland, with a small proportion of vehicles accounting for a substantial share of the total emissions. According to the researchers, approximately 50% of all particle emissions are generated by 10% of ICE vehicles during motorway driving and by 5% of ICE vehicles while idling during periodic technical inspections (PTIs).
“We discovered that new ICE vehicles generate particle emissions that are, on average, 70% lower than those of older models under real driving conditions on motorways. The most effective way to improve air quality is to focus on the most polluting cars, instead of relying on general actions applied to all cars,” says Postdoctoral Research Fellow Ville Leinonen, who specialises in aerosol physics at Tampere University.
Leinonen expects that the scrapping premium (in Finnish), which was introduced by the Finnish Government at the beginning of 2026 for owners of cars that are more than ten years old, will reduce total particle emissions by accelerating the transition to new low‑emission vehicles.
Vehicle age and engine size affect emissions
Statistical modelling conducted during the study demonstrated that vehicle characteristics, especially engine size and year of first registration, significantly influence particle emission levels. Clear differences were observed between petrol and diesel cars.
“The measurements we carried out during PTIs showed that particle emissions have decreased in diesel cars taken into use from 2011 onwards due to the introduction of diesel particulate filters, whereas emissions from petrol cars have remained largely unchanged since the early 2000s. Particle emissions from Euro 5 and Euro 6 petrol cars were found to be higher than those of comparable diesel cars,” says Assistant Professor Panu Karjalainen from Tampere University.
Emissions produced under real driving conditions were only slightly lower for petrol cars than for diesel cars.
“As fine particles emitted by ICE vehicles have a substantial effect on air quality, particularly in urban areas, air quality could be markedly improved through actions targeted at a small proportion of vehicles,” emphasises Research Director Santtu Mikkonen from the University of Eastern Finland.
The Euro standards are EU‑wide regulations that set limits on harmful exhaust emissions from vehicles. In this system, the higher the number, the stricter the limits (Euro 2 – Euro 6).
Particle emission levels must be continuously monitored
While PTIs are effective in identifying high‑polluting vehicles, the researchers emphasise that achieving meaningful environmental benefits will also require effective policy measures, corrective action and continuous monitoring. Santtu Mikkonen believes that the particle measurements recommended by the EU will eventually be incorporated into PTIs in Finland as well.
In Finland, particle emissions from vehicles are expected to decline rapidly if consumers increasingly choose electric vehicles to replace older, high‑polluting cars. At the same time, the relative contribution of other emission sources to overall air quality will grow. Non-exhaust particle emissions are also generated by tyre and brake wear as well as the abrasion of paved road surfaces.
“The statistical modelling method we used in the study can also be applied to other forms of air pollution, such as nitrogen oxides, black carbon and particulate matter,” the researchers point out.
The study, conducted in collaboration between Tampere University, the University of Eastern Finland and Dekati Oy, analysed particle data collected during hundreds of periodic technical inspections of vehicles in Finland, alongside measurement data gathered during an earlier study under real driving conditions on motorways. Combined, these datasets provide a broadly representative picture of the passenger car fleet in Finland and enable a comparison between emissions generated while idling and driving.
The article, titled Detection of high-emitters: Variables affecting particle number emissions in Finnish vehicle fleet, was published in Transportation Research on 6 November 2025.
Further information
Ville Leinonen
Tel. +358 50 379 8430
ville.leinonen [at] tuni.fi
Panu Karjalainen
Tel. +358 45 359 2979
panu.karjalainen [at] tuni.fi
Santtu Mikkonen
Tel. +358 40 355 2319
santtu.mikkonen [at] uef.fi
