Auckland has an overlooked traffic pollution problem—and it's not from exhausts

Auckland, a city renowned for its progressive environmental policies, faces an unexpected challenge in its ongoing battle against traffic pollution—non-exhaust emissions. While cleaner engine standards and the rise of electric vehicles have contributed to improved air quality, researchers have discovered that not all pollution comes from vehicle exhaust pipes.

The culprit? Road dust. Generated by wear and tear on tires and brakes, erosion of road surfaces, and the kicking up of dust by passing vehicles, this invisible pollutant poses a significant challenge to policymakers. Despite the decline in exhaust emissions, road dust remains a major contributor to Auckland’s particulate pollution, as highlighted in a new study published in the Journal of the Royal Society of New Zealand.

Through an analysis of data from 2006 to 2019, researchers identified three key monitoring sites in Auckland: Queen Street in the city center, the Khyber Pass on a major arterial route, and Penrose near a key highway corridor. By examining air-quality data alongside traffic and weather conditions, the study found that road dust had a stronger association with PM₁₀ levels—the measurement for airborne particles smaller than 10 micrometers—than vehicle exhaust pollution did.

Interestingly, even though heavy vehicles make up only 4% of traffic, they were strongly linked to increased PM₁₀ levels. This finding suggests that heavy vehicles may contribute to dust resuspension, possibly due to their weight disturbing soil and loose material on roads. Weather conditions also played a role, with stronger winds associated with higher PM₁₀ levels when road dust concentrations were elevated, while rainfall had no significant effect.

The implications of these findings are significant. While exhaust pollution from vehicles is relatively straightforward to address through emission standards, road dust presents a more complex challenge. It originates from multiple sources, can be repeatedly disturbed by traffic, and falls outside conventional vehicle-emission standards. Nevertheless, non-exhaust emissions are linked to serious health issues, including cardiovascular and respiratory problems.

To mitigate the risks associated with road dust, policymakers will need to adopt a more targeted approach. This could involve better containment measures for soil and loose material near roads, improved management of road dust, and targeted controls on heavy-vehicle movements in pollution hotspots. Additionally, reducing traffic volumes through enhanced public transportation and infrastructure for walking and cycling could also help lessen the burden of non-exhaust emissions.

The study, which covers only three Auckland sites from 2006 to 2019, underscores the need for wider and more recent monitoring to assess the impact of newer vehicle technology, heavier vehicles, and changing travel patterns on non-exhaust pollution. However, the broader challenge is clear: as tailpipe emissions decline, transportation and air-quality policies must increasingly account for the pollution generated simply by vehicles moving on roads. Otherwise, Auckland risks overlooking a significant source of its particulate pollution.