 The EPA rating for the model year 2011 Volt 's tailpipe emissions is 84 grams of CO2 per mile , ( 52 @.@ 5 CO2 g / km ) . Tailpipe emissions for the improved model year 2014 / 15 Volt fell to 81 grams of CO2 per mile , ( 50 @.@ 6 CO2 g / km ) . CO2 emissions are produced by the internal combustion engine in extended @-@ range mode , and only after the Volt 's primary battery charge has been depleted . In the other air pollutants category , the Volt rates six out of ten , with ten being best . 
