As a result of vehicle emission regulations, the bulk of particulate matter emissions from road traffic now arises from non-exhaust sources, including road dust resuspension. Although much is known about the atmospheric chemistry of desert dust, comparatively little is known regarding that of road dust. Here, we show that road dust and other photoactive minerals can participate in sulfate radical-mediated chemistry and thereby promote the formation of organosulfates (ROSO3–), a compound class that comprises a substantial fraction of organic aerosol mass. In addition, we show that road dust is a source of singlet oxygen (1O2) and hydroxyl radical, two important environmental oxidants, and that both bulk road dust and brake wear particles promote the photochemical loss of ozone, an important urban pollutant. Together, these results suggest that road dust photochemistry has the potential to influence both the lifetimes of pollutants present at the dust surface and the composition of the surrounding urban atmosphere.
As a result of climate change, urban air quality is also increasingly influenced by wildfire emissions. A major contributor to the particulate matter component of wildfire emissions is brown carbon (BrC), a class of light-absorbing organic carbon that can influence climate by altering Earth’s radiative balance. Here, we use size-exclusion chromatography with diode-array UV-Vis detection to characterize aqueous extracts of BrC produced via combustion of boreal peat samples obtained in northern Alberta. We show that the molecular size of light-absorbing species changes with mobile phase composition, and in particular provide evidence that apparent “humic-like” species in these extracts consist in part of weakly bound aggregates of smaller molecules. These results highlight the need for careful method development and data interpretation when employing size-exclusion chromatography for the study of BrC optical properties.
Sarah A. Styler is an Assistant Professor of Environmental Chemistry and Canada Research Chair in Atmospheric Chemistry at the University of Alberta, where her research group studies the chemistry and health/climate impacts of dust and wildfire emissions.