Wear and tear from brakes, tires and road surfaces will soon overtake car exhaust fumes as the leading source of fine particles released into the air by road traffic, according to a new OECD report. Heavy electric vehicles with long-distance batteries could compound the problem even as they slash emissions from engine exhaust.

Percentage of total PM emissions from road transport. Source: OECD

The findings in Non-exhaust Particulate Emissions from Road Transport: An ignored Environmental Policy Challenge also suggest that electric vehicles should not be exempted from tolls and congestion charges aimed at reducing road traffic emissions.

In the context of growing travel demand, electric vehicles are widely regarded as a solution to mitigating greenhouse gas emissions and other air pollutants from road transport. While they stand to eliminate exhaust emissions, this report shows that electric vehicles are not likely to provide substantial benefits in terms of non-exhaust emissions reductions.

Regenerative braking systems can reduce brake wear, but tyre wear, road wear, and road dust resuspension remain significant sources of non-exhaust emissions from electric vehicles. Non-exhaust emissions from these sources can in fact be higher for electric vehicles than for their conventional counterparts, as the heavy batteries in electric vehicles imply that they typically weigh more than similar conventional vehicles. This is particularly the case for electric vehicles with greater autonomy (driving range) that require larger battery packs.

—“Non-exhaust Particulate Emissions from Road Transport”

Instead, road traffic regulations should consider both exhaust and non-exhaust emissions from all vehicles and should take into account factors such as vehicle weight and tire composition. Policy makers should also favor measures that reduce driving distances, limit urban vehicle access and encourage public transport, walking and cycling.

Exposure to airborne particulate matter (PM) is associated with acute respiratory infections, lung cancer, and chronic respiratory and cardiovascular diseases. Road traffic is behind a quarter of PM_2.5, the most damaging type, in urban areas yet only exhaust emissions of PM are regulated. No standards exist for measuring or regulating non-exhaust PM emissions.

As particulate matter emitted from exhaust sources decreases with the uptake of electric vehicles, the majority of PM released into the air by road traffic could come from non-exhaust sources as early as 2035.

The amount of non-exhaust particulate matter a vehicle emits is determined by many factors, including vehicle weight, driving styles, the material composition of brakes, tires and roads, and the amount of dust on road surfaces.

Lightweight electric vehicles with a driving range of about 100 miles (161 km) emit an estimated 11-13% less PM_2.5 than conventional vehicles in the same segment. However, heavier electric vehicles with battery packs enabling a range of 300 miles (483 km) emit an estimated 3-8% more PM_2.5 than equivalent conventional vehicles.

The report finds that the total amount of non-exhaust particulate matter emitted by passenger vehicles worldwide is likely to rise by 53.5% by 2030.

These findings underline the need to establish standardised approaches to measuring non-exhaust particulate matter and to develop a better understanding of how factors like vehicle characteristics influence the amount of PM generated, the report says.

Resources

• OECD (2020), Non-exhaust Particulate Emissions from Road Transport: An Ignored Environmental Policy Challenge, OECD Publishing, Paris, doi: 10.1787/4a4dc6ca-en.