Exploring the influence of organic content and road type on photochemical oxidant production by urban road dust

In Canada and the United States, the largest anthropogenic source of primary fine particulate matter is road dust, which consists of brake and tire wear, pavement particles, crustal material, semi-volatile vehicle exhaust components, and natural organic matter. Although road dust research to date has mainly focused on its direct influence on human health, our group has previously shown that road dust is a photochemical source of singlet oxygen, an important environmental oxidant. Here, we report singlet oxygen and hydroxyl radical production by aqueous suspensions prepared from eight road dust samples collected from three different road types (residential, arterial, and expressway) in Toronto, Canada. To extrapolate our results to conditions typical of aqueous aerosol, we also quantified oxidant production as a function of aqueous-phase dust loadings. In addition, we compared the quantum yields for singlet oxygen production by aqueous road dust extracts to those previously reported for dissolved organic matter from other sources in aqueous aerosol and aquatic environments. These results highlight the photochemical activity of road dust, as well as its potential to influence the lifetime of urban pollutants.