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Near-Road Modeling and Measurement of Particles Generated by Nanoparticle Diesel Fuel Additive Use
Citation:
Gantt, B., S. Hoque, R. Willis, K. Fahey, J. Delgado-Saborit, R. Harrison, G. Erdakos, P. Bhave, M. Zhang, H. Pye, AND K. Kovalcik. Near-Road Modeling and Measurement of Particles Generated by Nanoparticle Diesel Fuel Additive Use. AAAR 33rd Annual Conference, Orlanda, FL, October 23, 2014.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA mission to protect human health and the environment. AMAD research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
Cerium oxide (ceria) nanoparticles (n-Ce) are used as a fuel-borne catalyst in diesel engines to reduce particulate emissions, yet the environmental and human health impacts of the ceria-doped diesel exhaust aerosols are not well understood. To bridge the gap between emission measurements and ambient impacts, size-resolved measurements of ambient aerosol composition and mass concentration have been performed in Newcastle-upon-Tyne, United Kingdom, where an n-Ce additive has been in continuous use in a bus fleet since 2005. These observations show that the cerium aerosol fraction thought to be of non-crustal origin and associated with the use of n-Ce has a mass size distribution peaking at 200 nm in aerodynamic diameter and a mass concentration of ~0.3 ng per cubic meter. The diurnal cycle of the observed cerium aerosol concentrations suggests that n-Ce use in Newcastle buses is a significant source of cerium at the measurement site. Simulations with a near-roadway multi-component sectional aerosol dynamic model predict that the use of n-Ce additives changes the size distribution of emitted aerosols such that the number concentration of nuclei mode aerosols (< 50 nm in diameter) increases but the total mass concentration decreases. In the atmosphere, dilution and deposition leave < 25% ofthe emitted aerosol number concentration remaining 300 meters downwind from the roadway. The near-road model predicts a downwind cerium aerosol mass size distribution peaking at 150 nm in aerodynamic diameter, a value similar to that measured for non-crustal cerium in Newcastle. The diameter at the peak of the cerium aerosol mass size distribution is predicted to increase by 35 nm in the ambient atmosphere (300 meters downwind from the roadway) due to condensation of organic gases onto the cerium-containing aerosols.
