How New Auto Fuels Will Affect Air Quality in an Era of Climate Change

Photo: Michael Kleeman talking to reporter Nikki Modero
UC Davis professor Michael Kleeman is interviewed by reporter Nikki Modero of KFBK-AM radio, Sacramento. Photo credit: Karin Higgins, UC Davis.

As millions of cars and trucks hit the road using fuels other than gasoline, the U.S. Environmental Protection Agency is funding a $900,000 research project at UC Davis to learn precisely what emissions those alternative-fuel vehicles produce and how climate change might affect those emissions.

The research is urgently needed to improve forecasts of how climate change will affect air quality in California, said Michael Kleeman, who is the project's lead researcher and a UC Davis professor of civil and environmental engineering.

"We know from past studies that motor vehicles are a major source of airborne particles in California and across the United States, and higher concentrations of airborne particles are associated with higher death rates. So public agencies are already working to reduce vehicle emissions to protect public health," Kleeman said.

"Now comes climate change, with shifts in patterns of air temperature and humidity levels. Those shifts will affect the particle emissions from cars and trucks and how those particles age in the atmosphere. So the net effect of climate change on vehicle emissions in the coming decades has major public health implications in California."

Wayne Nastri, the EPA's regional administrator for the Pacific Southwest, added: "Given our complex air quality challenges, we must take an integrated approach to environmental protection using new technologies, cost-effective approaches that improve energy efficiency and cleaner fuels."

Kleeman will collaborate on the four-year study with Shuhua Chen, an associate professor of atmospheric science at UC Davis with extensive experience in regional climate models, and James Schauer, a professor of civil and environmental engineering at the University of Wisconsin-Madison who is a leading expert in the analysis of airborne-particle chemical composition.

The researchers will take hundreds of air samples from exhaust pipes of alternative-fuel vehicles and analyze the size and chemical composition of the exhaust particles under a range of temperature and humidity conditions.

The vehicles they will sample include:

  • E-85 cars and light-duty trucks, also called flex-fuel or ethanol-blend vehicles;
  • Gasoline-electric hybrid cars, such as the Toyota Prius and Honda Civic;
  • Plug-in hybrid electric cars; and
  • Heavy-duty trucks powered by biodiesel.

Based on past studies, Kleeman and Schauer expect that each exhaust particle will consist mostly of carbonaceous compounds produced when fuel and oil are burned in the engine. One of the goals of the current project is to better understand exactly which compounds are emitted under various temperature and humidity conditions.

This information will be incorporated into state-of-the-science air-pollution and regional-climate models running on hundreds of computers at UC Davis. The researchers will use the improved input data in their models to better predict how future transportation exhaust particles will age in a warmer atmosphere and what this might mean for public health.

In a related project also funded by the U.S. EPA, Kleeman and co-workers will assess how the rise in zero-emission vehicles, such as all-electric vehicles and fuel-cell hybrid vehicles (which run on hydrogen), will affect future air quality in California.

Even though these vehicles have no tailpipe emissions, there may be emissions produced when their electric or hydrogen fuels are manufactured.

About U.S. EPA's Region 9 Air Program

The U.S. EPA's Transportation and Air Quality program protects public health and the environment by regulating air pollution from motor vehicles, engines and the fuels used to operate them, and by encouraging travel choices that minimize emissions. U.S. EPA's Region 9 Air Program guides the federal management, implementation, enforcement and technical oversight of air quality in California, Arizona, Nevada, Hawaii, the Pacific Islands, and Tribal Nations.

About UC Davis

The University of California is one of the world's foremost research and teaching institutions, and UC Davis, which celebrates its centennial this upcoming academic year, is the UC's flagship campus for environmental studies. UC Davis is a global leader in environmental studies relating to air and water pollution; water and land use; agricultural practices; endangered species management; invasive plants and animals; climate change; resource economics; information technology; and human society and culture. One in six of UC Davis' 1,500 faculty members specializes in an environment-related subject.

Media Resources

Michael Kleeman, UC Davis Civil and Environmental Engineering, (530) 752-8386,

James Schauer, University of Wisconsin-Madison, (608) 262-4495,

Niloufar Glosson, U.S. EPA, (415) 972-3684,