 The widespread use of ethanol brought several environmental benefits to urban centers regarding air pollution. Lead additives to gasoline were reduced through the 1980s as the amount of ethanol blended in the fuel was increased, and these additives were completely eliminated by 1991. The addition of ethanol blends instead of lead to gasoline lowered the total carbon monoxide (CO), hydrocarbons, sulfur emissions, and particulate matter significantly. The use of ethanol-only vehicles has also reduced CO emissions drastically. Before the Pró-Álcool Program started, when gasoline was the only fuel in use, CO emissions were higher than 50 g / km driven; they had been reduced to less than 5.8 g / km in 1995. Several studies have also shown that São Paulo has benefit with significantly less air pollution thanks to ethanol's cleaner emissions. Furthermore, Brazilian flex-fuel engines are being designed with higher compression ratios, taking advantage of the higher ethanol blends and maximizing the benefits of the higher oxygen content of ethanol, resulting in lower emissions and improving fuel efficiency.
