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Researchers Examine Nanoparticles' Impact on Fuel Emissions and Air Pollution

Double-decker bus in Europe

Issue:

Particulate matter, or PM — a major component of air pollution — has many sources. It can originate from natural processes, like forest fires and wind erosion, and from human activities like agricultural practices, smokestacks, construction, and car emissions. Exposure to air with high levels of PM can result in respiratory health problems and depressed cardio-vascular function.

Private industry has developed several fuel additives designed to decrease the amount of PM in diesel exhaust and increase fuel efficiency. Several of these use a nanoparticle called cerium oxide as their active ingredient. To assess the impact of cerium oxide nanoparticles on human health and the environment, especially near roadways where people may face higher levels of exposure, scientists have studied how these nanoparticles affect motor vehicle exhaust and air quality and how they behave near roadways.

Action:

EPA used a model to examine how cerium oxide changes fuel emissions — including the size and composition of particles and gases emitted. The model predictions were used to understand data collected from a 2012 field study in England where EPA scientists worked with colleagues from the U.K. to sample air in areas where cerium oxide-based fuel additives were being used in diesel buses. Researchers also looked at how these particles move from roadways to areas near roads where people may live and work.

Results and Impacts:

To help regional modelers, exposure scientists, and policymakers better understand the potential environmental and human health impacts of cerium oxide additive use in diesel fuel, researchers combined ambient observations and modeling to determine the magnitude, size, and atmospheric evolution of cerium-containing particles.

While some previous results suggest that the human health risks associated with cerium oxide nanoparticles in the ambient atmosphere are likely to be low, acceptable levels of cerium in the atmosphere — which is likely a function of particle size — is still uncertain. This is because environmental and human health toxicity studies do not always use cerium particles with a size distribution representative of laboratory and ambient measurements. Additionally, roadside modeling simulations indicated that for regional scale air quality considerations, the use of a cerium oxide additive may be beneficial due to the improved fuel economy and reduced emissions of exhaust particles.

To determine an acceptable ambient level of atmospheric cerium concentrations, future exposure studies should determine impacts as a function of size and composition, in addition to the mass concentration.

Below are two relevant publications from this research:

Gantt, B., S. Hoque, R. Willis, K. Fahey, J. M. Delgado-Saborit, G. Erdakos, R. M. Harrison, P. Bhave, K. M. Zhang, K. Kovalcik, and H. O. T. Pye, Near-road modeling and measurement of cerium-containing particles generated by nanoparticle diesel fuel additive use, Environ. Sci. Technol., doi: 10.1021/es502169p, 2014.

Gantt, B., S. Hoque, K. Fahey, R. D. Willis, J. M. Delgado-Saborit, R. Harrison, K. M. Zhang, D. Jefferson, M. Kalberer, K. Bunker, J. Conny, P. Bhave, J. Weinstein, H. O. T. Pye, Factors affecting the ambient physicochemical properties of cerium-containing particles generated by nanoparticle diesel fuel additive use, Aerosol Sci. Technol., doi: 10.1080/02786826.2015.1027809, 2015.

Contact:

Havala Pye (pye.havala@epa.gov)