You may remember the price of gas tends to go up right around Memorial Day every May. Prices of gasoline tend to go up, most people think, because of the increase in travel during the summer time which increases demand. Oil companies also conduct maintenance on their refineries in the spring, which limits output capacity temporarily. But another reason most people don’t realize is that the gasoline produced in the summer is much different than winter gasoline! This difference also makes it more expensive to produce gas in the summer than in the winter. Let’s take a look at the differences between summer and winter gasoline.
The Seasonal Transition
The seasonal gasoline transition happens twice a year and is the biggest reason for the price hike in the summer and price drop in the winter. This transition started as part of the Reformulated Gasoline Program in 1995, which was established by the EPA as part of amendments to the 1990 Clean Air Act. This was designed to reduce pollution and smog during the summer ozone season.
How Summer Gasoline Reduces Pollution
Summer gas uses a different blend of fuel additives than winter gasoline. These blends of additives burn cleaner and also, according to the EPA, encourage the research and development of alternative fuels. This means summer blends of gasoline produce less smog and release less toxic air pollutants.
The Reid Vapor Pressure
Winter gasoline also has a higher Reid Vapor Pressure (RVP) than summer fuel. RVP is a measure of the pressure of gasoline at 100 degrees Fahrenheit. The higher the RVP, the more easily that fuel evaporates. This is a particular concern for environmentalists because fuel which evaporates more easily also contributes faster to ozone formation, which is a problem during the ozone-forming summer months. Gasoline needs to have an RVP below normal atmospheric pressure (around 14.7 PSI), or else excess pressure would build in the gas tank causing it to boil and evaporate. Usually, summer blends of gasoline are mandated to be below 9 or 7.8 PSI. Winter gasoline has a higher PSI because it contains more butane in the additive blend, and since butane is less expensive than other fuel additives, this contributes to the drop in gasoline prices with the onset of fall.
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