Factors Affecting the Ambient Physicochemical Properties of Cerium-Containing Particles Generated by Nanoparticle Diesel Fuel Additive Use
Brett Gantt, Shamia Hoque, Kathleen M. Fahey, Robert D. Willis, Juana Maria Delgado-Saborit, Roy M. Harrison, K. Max Zhang, David A. Jefferson, Markus Kalberer, Kristin L. Bunker, Joseph M. Conny, Prakash V. Bhave, Jason P. Weinstein & Havala O.T. Pye, “Factors Affecting the Ambient Physicochemical Properties of Cerium-Containing Particles Generated by Nanoparticle Diesel Fuel Additive Use” Aerosol Science and Technology. February 2015.
Despite the use of cerium oxide nanoparticles (nCe) in some regions as a diesel fuel additive, the physicochemical properties of the resulting exhaust particles in the ambient atmosphere are not well known. The mixing state of ceria with other exhaust particles is one such physicochemical property that has been shown to potentially affect ecosystem/human health. In this study, cerium-containing particles associated with an nCe additive were collected in the laboratory and in Newcastle-upon-Tyne, U.K. where the local bus fleet uses the EnviroxTM nCe additive. Electron microscopy of laboratory-generated exhaust samples indicated both individual ceria and soot particles (external mixture) and ceria contained within soot agglomerations (internal mixture). Low ambient concentrations prevented quantification of the ceria particle mixing state in the atmosphere; therefore, a multi-component sectional aerosol dynamic model was used to predict the size, chemical composition, and mixing state of ceria particles as a function of distance from an idealized roadway. Model simulations predicted that most ceria particles remain non-mixed in the ambient atmosphere (300 meters downwind from the roadway) due to slow coagulation, with the mixing rate most sensitive to the ceria content of emitted nuclei-mode particles and the particle concentration upwind of the road. Although microscopy analysis showed both external and internal mixtures of ceria and soot in freshly-emitted particles, the ambient mass concentration and size distribution of ceria particles predicted by the model was insensitive to the emitted mixing state.