Gasoline -- Fun Fact

The main difference between winter- and summer-grade gasoline is their vapor pressure. Gasoline vapor pressure is important for an automobile engine to work properly. During cold winter months, vapor pressure must be high enough for the engine to start easily. Gasoline evaporates more easily in warm weather, releasing more volatile organic compounds which contribute to health problems and the formation of ground-level ozone and smog. In order to cut down on pollution, the Environmental Protection Agency (EPA) requires petroleum refiners to reduce the vapor pressure of gasoline used during the summer months.