Road dust and other non-exhaust vehicle emissions are making a significant contribution to Auckland’s air pollution, with heavy vehicles potentially having a disproportionate impact, new research finds.
A 13-year University of Auckland study found road dust was a significant contributor to PM10 — airborne particulate matter measuring 10 micrometres or less that is associated with respiratory and cardiovascular health problems.
Published in the Journal of the Royal Society of New Zealand, the research analysed air-quality data from monitoring sites in Queen Street, Khyber Pass and Penrose.
Researchers examined contributions to PM10 from soil, fuel, biomass burning, secondary sulphate, marine aerosol and road dust, combining the results with traffic, temperature, wind and rainfall data.
Lead researcher Dr Mingyue Selena Sheng, from the University of Auckland Business School’s Energy Centre, says the findings demonstrate the need to consider pollution generated by vehicles beyond exhaust emissions.
“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 brake, tyre, clutch and road-surface wear, as well as material deposited on roads and subsequently lifted back into the air by passing vehicles and atmospheric conditions.
In one analysis, road dust had a larger estimated effect on PM10 concentrations than fuel emissions. The modelling suggests a 1% increase in road dust is associated with an 8.8% increase in PM10 concentration.
Co-author and Business School economist Dr Le Wen says the findings are particularly relevant to heavy vehicles.
Vehicles weighing more than 3.5 tonnes represented about 4% of traffic in the dataset, with researchers finding an association between a higher proportion of heavy vehicles and increased PM10 levels.
Although they make up a relatively small proportion of traffic, Wen says heavy vehicles can play a disproportionate role in resuspending road dust and contributing to particulate pollution.
The researchers say the issue also has implications for the transition to electric vehicles, which are typically heavier than comparable combustion-engine vehicles 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 measures to reduce non-exhaust emissions could include requiring vehicles carrying soil and other loose material to keep loads contained in urban areas, as well as considering time-based restrictions to reduce pollution during peak periods.
