Electric vehicles may have higher particulate emissions from tires, but they usually have lower particulate emissions from other sources

By one estimate, 18% of new cars sold around the world in 2023 were battery electric vehicles (BEVs)^[1]. Continuing to electrify the globe’s road fleet will reduce the CO₂ pumped into the atmosphere by internal combustion engine vehicles (ICEVs). But skeptics claim that more BEVs will lead to a rise in particulate matter (PM) emissions, which largely do not come from vehicle exhaust.

The claim recently re-emerged in a Wall Street Journal opinion piece, which cited two non-peer-reviewed reports from British emissions testing company, Emissions Analytics. Five days later, a now-deleted article from LifeSiteNews.com cited one of the same reports to make a more extreme claim that “during a 1,000 mile journey, [BEVs] release 1,850 times more pollutants into the surrounding environment than gas-powered vehicles.” Variants of these claims, sometimes citing the same report that LifeSiteNews.com cited, circulated on other social media sites in the following weeks.

There is some evidence to suggest that, because BEVs are typically heavier than comparable ICEVs, BEVs’ tires will wear more quickly and create more PM emissions than ICEVs’ tires. However, BEVs typically use regenerative brakes, which emit fewer PM emissions than ICEVs’ traditional brakes. The reduction can exceed the PM emissions increase from the tires, and there are many scenarios in which a BEV can emit fewer particulates than a comparable ICEV – especially if a driver heavily uses their brakes – although further research is necessary to better understand this relationship. Below we will also explain why the more extreme version of this claim misrepresents the findings of the Emissions Analytics report.

Where PM emissions come from

PM emissions can come from vehicle exhaust, but as the Wall Street Journal correctly points out, internal combustion engines now face tighter tailpipe emissions standards like the European Union-mandated Euro 6, which severely restrict a vehicle’s tailpipe PM emissions in order to improve air quality. Vehicle manufacturers must now install particulate filters or other parts that have reduced PM emissions from the tailpipe. 

However, a vehicle can create PM emissions from other sources. Friction from a car’s brakes or from a car’s tires rubbing against the road can release particulate matter. Additionally, moving vehicles kick up dust and debris from the road beneath them in a process called road abrasion. 

The resulting PM emissions can include heavy metals (such as zinc or lead) and organic compounds (such as isoprene and polycyclic aromatic hydrocarbons). Human exposure to these particulates and compounds has been linked to skin irritation, respiratory and gastrointestinal issues, and cell damage; if they enter the environment, they can be toxic to wildlife^[2,3].

More than 90 percent of vehicular PM10 emissions (which consist of particles with diameters smaller than 10 micrometers) and 85 percent of vehicular PM2.5 emissions (which consist of particles with diameters smaller than 2.5 micrometers) now come from non-tailpipe sources like tires, brakes, and road abrasion^[4].

The claims

Although both ICEVs and BEVs have multiple PM emissions sources, as we have shown, the Wall Street Journal focused on only one of them: the PM emissions from tires. The opinion piece cited two Emissions Analytics reports to claim that tires were the dominant source of an ICEV’s PM emissions and that a BEV’s heavier weight would increase those emissions.

First, it cited a 2022 report as evidence that non-tailpipe emissions were the dominant source of an ICEV’s PM emissions. Emissions Analytics compared the PM emissions from an ICE vehicle’s tailpipe to the PM emissions from its tires. Emissions Analytics weighed an ICE vehicle’s wheels through the process of driving for 1,000 miles on real roads and used a “proprietary sampling system” to collect particles from each tire for measurement. (Science Feedback contacted Emissions Analytics, who confirmed Science Feedback’s understanding of their results.)

Emissions Analytics reported that, under normal driving, a vehicle released 1,850 times more particulate emissions from tires than from its tailpipe. The company has not released a more detailed methodology, nor has the study been peer-reviewed or published in the scientific literature. Without a detailed methodology, it is impossible for other groups to reproduce and verify Emissions Analytics’ results. In the absence of peer review, it is very difficult to assess the credibility of Emission Analytics’ study.

LIfeSiteNews and numerous social media posts have cited this single (again, non-peer-reviewed) report to claim that BEVs release 1,850 times more “pollutants” than comparable ICEVs. This claim is inaccurate on two counts. Firstly, even if this Emissions Analytics report is correct, it did not include any BEVs at all, which means that citations of this report misrepresent it and fail to support their claim. Additionally, Emissions Analytics focused on only one particular type of PM emissions — those coming from tires — not all PM emissions, and certainly not all pollutants.

One of the primary benefits of electrifying the world’s road fleet, for example, is a reduction of vehicle CO₂ emissions. It is true that the exact CO₂-emission reduction depends on the fossil fuel dependence of its electric grid, but even in high-fossil-fuel grids, BEVs do reduce emissions: A 2021 study from the International Council on Clean Transportation found that a BEV will be responsible, over the course of its life, for 66-69 percent fewer CO₂ emissions than a comparable gasoline ICEV in Europe, 60-68 percent fewer in the U.S., 37-45 percent fewer in China, and 19-34 percent fewer in India^[5]. BEVs do not emit more CO₂ than ICEVs, even when accounting for the CO₂ emissions from manufacturing a BEV and the CO₂ emissions from the electricity required to keep a BEV charged.

Returning to the less exaggerated Wall Street Journal claim, the opinion piece then cited a second Emissions Analytics report, released in 2023, which directly compared only the tire emissions from two vehicles: a BEV and a hybrid. The report found that the BEV released 26 percent more tire PM emissions than the hybrid. The study attributed the emissions to increased weight. Like the other report, Emissions Analytics has not released a detailed methodology, nor is it peer-reviewed, making its results impossible to independently verify.

Other peer-reviewed research does support the idea that increased weight leads to increased tire wear. Indeed, a BEV is approximately 20% heavier than a corresponding ICEV, and the increased weight does correlate to increased tire particulates^[6]. But the Wall Street Journal’s claim neglects non-tire PM emissions sources that other peer-reviewed research has studied – in particular, the PM emissions from brakes.

BEVs typically have lower brake emissions

Many electric vehicles rely on regenerative brakes, which do not primarily rely on friction like traditional brakes and therefore create fewer PM emissions. In scenarios where a driver brakes more frequently – driving in a dense urban setting, for instance – an electric vehicle would have reduced brake emissions. Analyses of PM emissions have demonstrated that the reduction can, in some circumstances, more than make up for the increased tire emissions^[6,7].

For example, a 2020 analysis accounted for PM emissions from tires, brakes, and road abrasion on city roads, rural roads, and motorways. Without regenerative braking, BEVs were responsible for more non-tailpipe PM2.5 and PM10 emissions than equivalent petrol or diesel vehicles in all three settings. However, when the analysis accounted for BEVs regenerative braking, BEVs had lower PM2.5 emissions than ICEVs overall and lower PM10 emissions in urban and rural settings, with only marginally higher PM10 emissions on motorways^[7]. 

A similar 2021 analysis from a different group found that a BEV’s PM2.5 and PM10 emissions did exceed those of a corresponding ICEV, especially on rural motorway roads – but if the BEVs included regenerative braking, the difference could be eliminated^[6]. Hesham Rakha, a transportation engineer at Virginia Tech who studies PM emissions, told Science Feedback that he has found that BEVs have 30 percent higher tire emissions than comparable ICEVs, but that, again, BEVs had lower brake emissions that offset the difference.

“While [BEVs] produce more tire emissions, they produce less brake emissions, and depending on the drive cycle, they can either be more efficient or less efficient,” Rakha told Science Feedback via email.

Additionally, changing brake material can make a significant impact on total PM emissions. The first study that experimentally tested emissions in a controlled setting, in 2022, found that, using non-asbestos organic brake pads, an electric vehicle was responsible for 10 to 17 percent more primary PM10 emissions (including both tailpipe and non-tailipipe sources) than either a gasoline- or diesel-powered vehicle. However, by replacing the vehicles’ brake pads with low-metallic ones, the electric vehicle was actually responsible for up to 34 percent fewer PM10 emissions^[8].

Conclusion

In summary, tire emissions are only one aspect of a vehicle’s PM emissions. Even if a BEV’s increased weight does increase its PM emissions from tires, both analytical and experimental evidence demonstrates that this BEV can have lower PM emissions from other sources, such as brakes, tires, and the tailpipe, which a BEV does not have. A comprehensive comparison of an ICEV and a BEV must account for all these sources, which the Wall Street Journal and other sources do not.

However, more experimental studies are needed in order to firmly establish how the non-exhaust PM emissions from electric vehicles compare to the non-exhaust PM emissions from ICEVs. In particular, many models do not account for secondary PM emissions, which arise when other pollutants react in the atmosphere to spawn particulates. When the authors of the aforementioned 2022 experimental analysis did account for secondary PM10 emissions, both non-asbestos organic and low-metallic brake pads resulted in lower PM10 emissions^[8].

That said, it is possible to reduce PM emissions from tires even with a switching to BEVs. For example, the European Union is preparing to introduce even stricter emissions standards – Euro 7 – which will institute first-ever restrictions on tire and brake emissions, restrictions that will also apply to BEVs. Tire manufacturers can respond by creating tires that are less prone to releasing PM emissions^[3].

Therefore, researchers say that the emissions research so far does not indicate that tire PM emissions are a reason to discourage the adoption of electric vehicles. “I don’t see this as a big issue,” Rakha told Science Feedback via email.

REFERENCES

• 1 – Global EV Outlook 2023. International Energy Agency.
• 2 – Baensch-Baltruschat et al (2020). Tyre and road wear particles (TRWP) – A review of generation, properties, emissions, human health risk, ecotoxicity, and fate in the environment. Science of The Total Environment.
• 3 – Tan et al (2023). Briefing: Tyre wear particles are toxic for us and the environment. Imperial College London.
• 4 – Timmers and Achten (2016) Non-exhaust PM emissions from electric vehicles. Atmospheric Environment.
• 5 – Bieker (2021). A Global Comparison of the Life-Cycle Greenhouse Gas Emissions of Combustion Engine and Electric Passenger Cars. The International Council on Clean Transportation.
• 6 – Liu et al. (2021) Comparative analysis of non-exhaust airborne particles from electric and internal combustion engine vehicles. Journal of Hazardous Materials.
• 7 – Beddows and Harrison (2021) PM10 and PM2.5 emission factors for non-exhaust particles from road vehicles: Dependence upon vehicle mass and implications for battery electric vehicles. Atmospheric Environment.
• 8 – Woo et al. (2023) Comparison of total PM emissions emitted from electric and internal combustion engine vehicles: An experimental analysis. Science of The Total Environment.