Given that butanol is an "oxygenate", oxides of nitrogen emissions should be lower than for gasoline.
Just look at the quote in the comments section
We should be really careful about all of these bio-engineered organisms. Did you know that the miracle BT gene has made it into corn as far as Mexico? Monsanto didn't predict that, and we don't know what will happen when (not if) these new Frankensteins get loose. In our rush to save the world and make a lot of money doing it, there should be some careful consideration of how to keep these Genies in the bottle.
So they already have ideas, the environmentalist movement is more about being anti-capitalist than being pro-environment