"Less pollution
Over a lifetime, from production to transportation, disposal and the energy used to power various cars, the electric and hybrid electric vehicles emitted less pollutants than conventional internal combustion engines. Kreider's study looked at carbon dioxide, sulfur oxide, nitrogen oxide and mercury levels emitted.

Cars running on natural gas, however, fared the best.

"A Prius (hybrid) is a lot better than a conventional car if we just focus on greenhouse gases, but then the question is, 'What's the best you can do?' " Kreider said.

"The point about electric vehicles is they're not that clean. To do it really clean, you'd do compressed natural gas."

http://www.chron.com/disp/story.mpl/business/energy/7301694.html