Road dust and other non-exhaust vehicle emissions are making a significant contribution to Auckland’s air pollution, according to new research examining more than a decade of air-quality data.
The 13-year study found road dust was a significant contributor to PM10 — airborne particulate matter measuring 10 micrometres or less that can affect respiratory and cardiovascular health.
Published in the Journal of the Royal Society of New Zealand, the research analysed data from three Auckland air-quality monitoring sites — Queen Street in the central city, Khyber Pass near the city centre and Penrose near a major motorway.
Researchers identified contributions to PM10 from soil, fuel, biomass burning, secondary sulphate, marine aerosol and road dust. They combined the results with traffic data and information on temperature, wind speed and rainfall to examine factors influencing concentrations.
Lead researcher Dr Mingyue Selena Sheng, from the University of Auckland Business School’s Energy Centre, says the findings highlight the need to look beyond vehicle exhaust emissions when considering transport’s effect on air quality.
“Our findings show that road dust is, at times, a dominant and statistically significant contributor,” Sheng says.
“Much of the focus has been on reducing what comes out of the tailpipe, but road dust and other non-exhaust emissions need our attention.”
Non-exhaust emissions include particles generated by the wear of brakes, tyres, clutches and road surfaces, along with dust and other material deposited on roads that is lifted back into the air by passing vehicles and atmospheric conditions.
In one analysis, road dust had a larger estimated effect on PM10 than fuel emissions. The researchers’ modelling suggests a 1% increase in road dust is likely to result in an 8.8% increase in PM10 concentration.
Co-author and University of Auckland Business School economist Dr Le Wen says non-exhaust emissions are closely linked to the physical movement of vehicles, meaning both the number and type of vehicles on the road can have an impact.
Heavy vehicles weighing more than 3.5 tonnes represented about 4% of traffic on average in the dataset, with researchers finding evidence of an association between a higher proportion of heavy vehicles and increased PM10 levels.
The findings also have implications for the transition to electric vehicles, which typically weigh more because of their batteries.
“While electric vehicles offer a pathway to reducing tailpipe emissions, their environmental benefits may be offset by increased non-exhaust emissions, especially from heavier vehicle fleets.
“Moving to electric vehicles has important benefits, but it doesn’t make particulate pollution from road transport disappear. If we want cleaner urban air, non-exhaust emissions need to be a key part of the conversation.”
The researchers say reducing non-exhaust emissions will require targeted measures alongside efforts to cut tailpipe pollution.
The study suggests transport policy could require vehicles carrying soil and other loose material to keep loads contained in urban areas and consider time-based restrictions to reduce air pollution during peak periods.
