Next time you fill up with regular; spare a thought for what the product went through to make it into your tank. Before you got a chance to put the pedal to the metal, the tiger in your tank had to treat a digestive problem that was causing too much gas. It was all in honor of something called Reid Vapor Pressure (RVP) regulations. Today we open the window on the issue to air the pungent details.
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RVP stands for "Reid Vapor Pressure" a measure of gasoline volatility indicated in pounds per square inch (PSI) at 100 degrees Fahrenheit. The higher a gasoline's RVP the more quickly it evaporates. The RVP for gasoline should always be below normal atmospheric pressure or 14.7 PSI. If the RVP gets higher than 14.7-PSI fuel might evaporate in the gas tank on a hot day resulting in a vapor locked engine (car won’t start) or worse yet, an explosion. At the same time you need a certain RVP level in the winter when it gets cold or your car won’t start because the fuel won’t vaporize in the carburetor.
The Unites States Clean Air Amendment Act of 1990 mandated reductions in toxic emissions in geographic areas that did not meet required pollution control standards (mostly cities). A principal target of the legislation was reduced emissions from gasoline of volatile organic compounds (VOC), nitrogen oxides (NOx), and carbon monoxide (CO). All things being equal, these emissions increase in fuels with higher RVP levels.
The U.S. Environmental Protection Agency (EPA) administers the Clean Air Act. To reduce auto emissions, particularly in polluted areas, the EPA has implemented gasoline volatility regulations establishing maximum allowable RVP levels for gasoline during the summer months – usually defined as June through September. Violations of the gasoline RVP regulations are subject to fines of up to $37,500 per day.
That all sounds like standard operational procedure for the EPA - but rest assured that things get complicated real quick from hereon in. For starters the country gets divided up into areas – in some cases down to the county level and below. Each area gets its own version of the regulations. This creates an RVP quagmire.