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 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 lead researcher Michael Kleeman, a 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," 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."

Kleeman is collaborating 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 plan to 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.

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 new research 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.