Surprising Science: How Electric Cars Transform Urban Air

“It’s not just the tailpipe y’all,” joked one Electrek commenter, alluding to the black discolorations on alloy wheels visible proof of a less infamous city pollutant: brake dust. For decades, exhaust emissions have been the focus of city-air cleaning initiatives, but a new wave of research indicates that the real story goes far beyond the muffler.

A trailblazing study by EIT Urban Mobility, surveying the busy streets of London, Milan, and Barcelona, has quantified a colossal 83% reduction in brake dust pollution from battery-electric cars compared to their combustion-engine counterparts. The breakthrough refocuses debate on clean air for urban areas onto non-exhaust emissions a field more widely recognized as an essential environmental health frontier.

The technology behind that shift is regenerative braking. As opposed to traditional friction brakes, which compress pads against discs to decelerate a vehicle emitting puffs of airborne particles electric vehicles use their motors spun backwards to decelerate, converting energy into electricity and storing it in the battery. This not only makes the system more efficient and extends the life of batteries, but lowers mechanical braking necessity by half, thereby substantially reducing airborne brake particle emissions.

Brake dust, composed of an intricate mixture of iron, copper, zinc, organic carbon, and other metals, is more than a surface nuisance. Scientific tests have determined that up to 55% of non-exhaust traffic-related PM10 in cities is emitted by brake wear. These particles are usually smaller than 10 microns and occasionally ultrafine below 100 nanometers in size and are easily inhaled and become stuck deep in the lungs. Studies using human alveolar cells have shown that copper-enriched brake dust initiates extreme oxidative stress and inflammation at times equalling or even surpassing the effect of diesel exhaust particles. The health effect is especially critical for urban disadvantaged groups, where exposure to partical matter has been shown to be related to increased asthma rates, cardiovascular disease, and other respiratory conditions.

While others have pointed to EVs’ marginally higher tire wear based on their greater average weight the EIT Urban Mobility study found that brake dust is far more likely to become airborne and contribute to air pollution than tire particles. Even when summing up emissions from tires, brakes, and road wear, BEVs produce 38% less particulate pollution than gas-powered cars before even considering their lack of tailpipe emissions.

The impact is real. California has proven in the real world that where take-up of zero-emission vehicles grows in an area, neighbourhood air pollution and asthma emergency admissions decline. Gains, however, are not equitable. Low-income neighborhoods, which often endure the highest pollution impacts, have seen slower EV uptake, demonstrating the necessity of access to clean transport on an equitable basis.

For policymakers and planners, these findings present a new set of priorities. As exhaust continues to decrease, non-exhaust sources, especially brake wear, will account for an ever-greater share of urban particulate pollution. The impending Euro 7 regulations, which will place standards on tire and brake emissions, reflect the shifting regulatory interest. At the same time, technological innovation is already in motion: some manufacturers are using enclosed brake drum systems on EVs, trapping particulates yet again, and tire makers are working on specialized compounds to reduce wear.

The EIT Urban Mobility report also refers to the bigger picture: moving commuters out of private cars and into public transport, cycling, or walking can achieve up to five times more reduction in non-exhaust emissions than individual electrification. But for the millions of cars that will still be on urban roads, the use of BEVs and their regenerative braking technology is a major step towards cleaner, healthier urban air.