SAN FRANCISCO (KCBS) — People who bought an electric car, thinking they were saving the environment, might be doing more harm than they think.

A new study says those plug-in vehicles can be making the air dirtier and worsening global warming depending on where you’re getting the electricity to charge that vehicle.

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KCBS Anchors Patti Reising and Jeff Bell spoke with study co-author Julian Marshall, an engineering professor at the University of Minnesota.

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“It depends on where the electricity comes from and that’s kind of one of the strongest findings here. You’re looking at the air pollution and health impacts,” Marshall said. “Electric vehicles and ethonal are sometimes offered up as environmental solutions and we found that’s not always the case.”

The study examines environmental costs for cars’ entire life cycle, including where power comes from and the environmental effects of building batteries.

“One of our findings—getting to the math, we found, is that electric vehicles powered by coal (have) several times—3 or 4 times—more air pollution related deaths from electric vehicles by coal then from the deaths from the same travel distance if driven in gasoline vehicles,” he said.

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But Marshall said that, right now, there aren’t a great number of electric vehicles on the road so that “the total amount of electricity they are using is not a lot.”