IIRC, it reduces certain noxious components of air pollution like particulates a...

DiabloD3 · on July 31, 2018

It lowers actual octane rating, thus increasing air pollution ever so slightly.

An engine designed entirely for ethanol, not one that just merely takes a mix but is meant for gasoline, would be higher efficiency and be worth it.

laurencerowe · on July 31, 2018

Ethanol has a higher octane rating (113 RON) than petroleum, but is less energy dense (so lowers mpg.)