Those areas of the country which do not meet minimum standards for air quality. The higher the number, the greater the octane rating of the gasoline. The higher the number, the slower burning the fuel - and the less likely your engine will knock. Today's new engines require a high octane fuel in order to run at peak efficiency. Typically, an octane rating of 90 is adequate for the majority of vehicles.
Ethanol typically adds three octane numbers when blended with gasoline.
Ethanol is an oxygenate, meaning that it adds oxygen to the fuel mixture. More oxygen helps the fuel burn more completely - reducing the amount of harmful emissions from the tailpipe. The ozone in the upper reaches of the earth's atmosphere helps protect us from ultraviolet radiation from the sun.