Study: Your all-electric car may not be so green.

"It's kind of hard to beat gasoline" for public and environmental health, said study co-author Julian Marshall, an engineering professor at the University of Minnesota. "A lot of the technologies that we think of as being clean ... are not better than gasoline."

The key is where the source of the electricity all-electric cars. If it comes from coal, the electric cars produce 3.6 times more soot and smog deaths than gas, because of the pollution made in generating the electricity, according to the study that is published Monday by the Proceedings of the National Academy of Sciences. They also are significantly worse at heat-trapping carbon dioxide that worsens global warming, it found. The study examines environmental costs for cars' entire life cycle, including where power comes from and the environmental effects of building batteries.

"Unfortunately, when a wire is connected to an electric vehicle at one end and a coal-fired power plant at the other end, the environmental consequences are worse than driving a normal gasoline-powered car," said Ken Caldeira of the Carnegie Institution for Science, who wasn't part of the study but praised it.

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The study finds all-electric vehicles cause 86 percent more deaths from air pollution than do cars powered by regular gasoline. Coal produces 39 percent of the country's electricity, according to the Department of Energy.

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