"A new study published Monday in the Proceedings of the National Academy of Sciences finds some electric cars actually make the air dirtier than gasoline-powered vehicles. The study assumes the energy that powers electric cars is coming from coal, which would mean the cars contribute more to soot and smog, and worsen global warming more than gasoline-powered cars. If the energy comes from other fuels, such as wind, water, or natural gas, the car’s carbon footprint is drastically lower. Oregon’s primary energy source is water."

http://www.oregonlive.com/environment/index.ssf/2014/12/some_electric_cars_are_big_air.html