Summer/winter and City/county gasoline?

Question

What is Summer/winter and City/county gasoline? Each city dictates what the blend suppose to be? Is there a gasolen switching for summer/winter? What is it?

Answer 1

Although drivers do not normally think about it, seasonal mix of gasoline has to do with the volatility of gasoline. The refineries automatically switch between summer and winter mixes. While cities are not usually involved in emissions, many states and federal regulations require a certain blend to sold in urban centers.

During hot summer days, gasoline with lower volatility are used in order to keep down emissions (the pollution that can case smogs). Excessive volatility also causes what is known as "vapor lock" in the fuel line (gasoline turns to valor in the fuel line).

During cold winter times, too little volatility can lead to a thick goop of mixture that can keep cars from starting in the morning.

Large urban centers regulate volatility in order to reduce the emission of unburned hydrocarbons. Large cities require the use of reformulated gasoline that is less prone to evaporation.

http://en.wikipedia.org/wiki/Gasoline