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Past Winner
2007 NSERC André Hamer Postgraduate Prize

Sarah Anne Styler

Master's Level

University of Toronto

Most people who live and work in cities are probably unaware that many of the solid surfaces that surround them – such as windows and facades of buildings – are actually giant chemical reactors that can influence the toxicity and persistence of air pollutants. While scientists have long known about the existence of these chemical reactors, also called urban grime or surface films, little is understood about precisely how they function.

New insights into urban grime are now beginning to emerge from experiments conducted by Sarah Styler, an environmental chemist at the University of Toronto. With the help of NSERC's André Hamer Postgraduate Prize for Master's Students, she has provided a better understanding of the role of sunlight in triggering chemical reactions between urban grime and the rich array of oxidants in city air.

"Urban surfaces are a huge medium for chemical reactions that are rarely considered by scientists who model atmospheric pollutants. It's a complex environment that hasn't really been studied much. Yet we know that you can't predict a chemical compound's toxicity and persistence in the environment if you don't take these huge urban surface areas into consideration,” Styler explains.

Urban grime forms when low-volatility chemical compounds, such as oxidized combustion products from vehicles, condense onto an impervious surface in a thin layer. For her master's experiments, Styler probed urban grime composed of pyrene, part of a group of chemical compounds from vehicle emissions known as polycyclic aromatic hydrocarbons (PAHs).

Using a laser-induced fluorescence technique, Styler examined whether sunlight enhances the oxidizing reaction between pyrene and ozone. She discovered that sunlight had no impact on the reactivity of pyrene incorporated into a model urban film. However, when the same experiment was performed with a solid film of pyrene, she found that the presence of light can double the compound's reaction rate with ozone.

Styler says her research was motivated by earlier experiments showing that when PAHs react with oxidants, the resulting by-products are often more toxic than the starting chemical compounds.

Having successfully completed her master's, Styler is now eagerly anticipating her next assignment. She is off to the prestigious Tate Gallery in London where she will assume a coveted internship as a conservation scientist. She will be working at the Tate Britain, one of a group of four world-renowned art galleries housing collections from the 16th century to the present.

"As a chemist who has recently adopted a keen interest in art, I'm really excited about the Tate opportunity. It's really a logical extension of my master's work because light and oxidants are just as important in art conservation as they are in atmospheric chemistry."