New U of A research highlights previously unidentified air quality impacts of winter road maintenance

When it comes to Edmonton’s winter roads, the focus is resolutely on the ground — how much and what type of precipitation has accumulated, and how quickly and efficiently it can be removed. Until now, little attention has been paid to the interactions between urban road dust and winter road maintenance materials with pollutant gasses, particularly as it pertains to the chloride-based anti-icers used by many municipalities, including Edmonton, to clear ice and improve safety. 

To mitigate the environmental impact of road salts like calcium chloride — a common, and controversial anti-icer — many northern municipalities have stepped back on its use or added agro-based materials such as molasses, corn and other agricultural products to reduce the total salt output, enhance ice-melting capacity and reduce corrosivity. 

A new University of Alberta study led by Maya Abou-Ghanem(‘21 PhD) suggests that these agro-based, commercial anti-icers react with ozone — a gas-phase pollutant and air quality indicator — in unforeseen ways and may provide a new chemical pathway for the release of chlorine-containing gasses, an important atmospheric oxidant, into wintertime urban atmospheres.

Up until now, the interactions between road dust—a complex mixture of road wear, gravel, rock salts, and plant debris—with gas-phase pollutants had not been explored. In this study, ozone was shown to react with samples of road dust collected in Edmonton, which was found to be much saltier than expected, prompting further study.

Under the supervision of environmental chemistry professor Sarah Styler, Abou-Ghanem and her team began looking at Edmonton’s road maintenance plans and found that along with road salting, agro-based anti-icers were also being used in certain parts of the city. 

“The calcium chloride used in Edmonton contains molasses, which we thought could be chemically interesting,” says Abou-Ghanem. “We studied the interaction between ozone and anti-icer and found this new reaction pathway that has never been shown nor heard of.”

The research highlights previously unidentified air quality impacts of road maintenance activities, but Abou-Ghanem says that while the release of chlorine containing gasses was surprising, the levels detected warrant consideration, not alarm.

“Chlorine can change the oxidizing capacity of the atmosphere because it is a powerful oxidant,” explains Abou-Ghanem. “But it’s important to note that there are so many reactions in the atmosphere and until this pathway gets put into atmospheric air pollution models, it's really hard to know the ultimate implications of what's happening. This would be an interesting next step.”

Styler agrees, and notes the need for further study to better understand the implications of this discovery. 

“It is releasing chlorine, but not at the level of whatever’s coming out of a swimming pool,” she says. “Its chemistry influences the chemistry of other pollutants in the atmosphere, and it does so in a way that can be different from other types of oxidants. There are a lot of different pieces to the overall environmental story, and this specific interaction is something that hasn't been studied at all.”

Abou-Ghanem has been researching airborne particulate matter for years. Throughout her PhD research in environmental chemistry, for which she received a Faculty of Science Distinguished Dissertation Award, she has focused on the heterogeneous chemistry of dust, primarily from desert origin but also anthropogenic dust in high-latitude urban areas like Edmonton. 

Now a NRC-RAP Postdoctoral Fellow at the National Oceanic and Atmospheric Administration in the United States, where she is investigating the chemical composition of aerosols using single-particle mass spectrometry, Abou-Ghanem hopes her research will prompt municipalities to consider air-road surface interactions when implementing winter road maintenance policies. 

“If these agro-based anti-icers are releasing a lot of chlorine, should they be using it? At the very least, it’s something that should be considered before making these decisions.”

The paper, Ozone uptake by urban road dust and first evidence for chlorine activation during ozone uptake by agro-based anti-icer: implications for wintertime air quality in high-latitude urban environments, will be highlighted in the Royal Society of Chemistry Emerging Investigator Series