The study took a look at what happened when the percentage of Sao Paolo's flex-fuel vehicles that ran specifically on gasoline (instead of the more common ethanol) jumped from 14 percent to 76 percent. The result was that ambient smog levels in the city fell about 20 percent. How that fuel-switching scenario was achieved or measured, we don't know, but there were plenty of vehicles to test, as about 40 percent of Sao Paulo's vehicles can run on either conventional gasoline or ethanol.
The Renewable Fuels Association (RFA) told AutoblogGreen that the Brazil results didn't apply to the US for reasons ranging from the differing emissions requirements to the different types of ethanol blends in Brazil (where sugar cane is used for ethanol instead of corn) to Sao Paulo's local climate.
"We are still examining the study and its supplemental material, but our initial review shows that the authors may have used a questionable methodology. The study didn't measure and characterize actual emissions coming from the tailpipes of vehicles nor the composition of the base gasoline to which the ethanol was added," said RFA CEO Bob Dinneen via email. "As the single most important factor in the formation of ozone will be the relative reactivity of the hydrocarbons coming from gasoline, this itself is a fatal flaw of the study."