Are roads more polluting than the cars we drive on them?

  Last updated September 7, 2020 at 12:10 pm

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Australian experts have responded to a US study that suggests asphalt during summer may be worse for pollution than petrol and diesel combined.


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We walk on it, we drive on it, but come summertime, asphalt may become a heavier polluter than unleaded and diesel from our cars combined, according to a US study released this week.


The team heated asphalt to temperatures between 40°C and 200°C and found that the pollutant emissions doubled between 40°C and 60°C – temperatures road surfaces regularly reach during summer.


The researchers found the asphalt emitted greater quantities of secondary organic aerosols (small particles which affect people’s health) than the cars that use the roads.


And although the emissions are highest when a new layer of asphalt was applied, and then reduced after a week, the chemicals kept being released in sunlight.




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Asphalt has been an overlooked source of pollutants


The University of Newcastle’s Dr Thava Palanisami describes the findings as “scary” because some of the detected emissions are “potentially carcinogenic“. He says the study findings are supported by his own work on toxicity.


But according to Macquarie University’s Dr Paul Harvey asphalt has been overlooked as a source of pollutants. And that’s a concern, he says, as “asphalt roads are globally ubiquitous”.


“In Australia a large proportion of the population lives within a few metres of asphalt surfaces, with the proximity decreasing in newer, more dense residential developments.


This study really demonstrates that the more humans move away from green spaces, the more we expose ourselves to potentially harmful pollutants in our lives. It serves as a wake-up call to regulators and town planners who may not see value in including green spaces and parkland in developments,” says Harvey.


Measurements of these types of emissions, termed ‘diffuse emissions’, have not been collected by Australia’s National Pollutant Inventory (NPI) since 1999, “possibly the result of the continuing financial squeeze on our national environment department,” adds Professor Ian Rae from the University of Melbourne.




Also: Four ways our cities can cut transport emissions in a hurry




In the study, the researchers identified the asphalt surface could have a larger detrimental effect to the atmosphere than other emissions. That includes both petrol and diesel cars.


And it’s a problem that is likely to get worse, says La Trobe University’s Dr George Domazetis. “Regulatory policies and technological advances will reduce emissions from motor vehicles…yet, the consumption of asphalt materials and their emissions are likely to remain the same or increase,” especially as temperatures rise due to climate change.


“This and similar studies are timely and show that dealing with GHG and related problems requires a broad approach.”


You can read the full Expert Reaction here.


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