A recent study by leading UK-based independent emissions testing company Emissions Analytics tested four apparently similar pairs of gasoline-fueled vehicles between the US (without gasoline particulate filters (GPFs)) and Europe (with GPFs). The US vehicles were tested in Michigan, and the European vehicles in the UK. The vehicles were:
3.0l BMW X5 (MY 2019 in US, MY 2020 in UK)
2.0l Jeep Wrangler (MY 2020 US and UK)
2.5l Toyota RAV4 Hybrid (MY 2019 US and UK)
1.5l Ford (MY 2020 Escape in US, MY 2020 Kuga in UK)
In each case, the European vehicle was equipped with a GPF, while the US vehicle was not, as a result of current regulatory requirements.
Each vehicle was then tested on similar on-road routes in the two countries to allow the comparison of their particle mass and number emissions. The gas emissions and particle number were measured using a regulatory-approved portable emissions measurement system (PEMS) from Sensors, Inc, together with a diffusion charger for particle mass measurement.
Similar on-road routes were designed in both locations, which, despite the inevitably different traffic and ambient conditions, were shown to have similar dynamics overall.
Average emissions across the four pairs of vehicles. Emissions Analytics.
Results were highly consistent between the four vehicles and between different types of driving, from urban cold start to highway warm start.
The average reduction in particle number was 86% across the different vehicles and driving; the variation was from 76% to 96%. The equivalent overall particle mass reduction was 55%, with 81% on highway.
A GPF system typically costs less than $200, which is about the same cost as the optional carpet mats on the BMW X5. Therefore, the cost for removing every billion particles emitted into the air is just 0.0004 cents. In addition to this, there is the further potential benefit of removing particles from the air that have come from other sources. As Emissions Analytics has shown … diesel particulate filters (DPFs) can ‘clean’ the air as the vehicle drives. GPFs are now achieving filtration efficiency rates—typically 80%, with the next generation of GPFs for Euro 7 regulations likely to exceed 95%—that are getting close to those of DPFs, and so the same net-cleaning effect can be expected. Moreover, the filtration efficiency tends to improve with the age of the filter, so the positive effect, if anything, grows.
… even as BEVs take off, there is growing evidence that they emit more tire wear emissions that ICE vehicles due to their increased weight. Emissions Analytics’ tests showed a 21% increase in tire particle mass emissions for 500 kg extra vehicle mass—roughly equivalent to the mass of a large battery pack—although this may be partially offset by the effect of regeneration breaking. More generally, there is an on-going trend towards heavier vehicles of all types, which increases tire emissions. Even though only 10-20% of tire wear emissions hang in the air, GPFs could have the added benefit of removing these particles from the air. In other words, ‘legacy’ ICE vehicles could help clean up emissions from BEVs.