Gasoline Additives

During WWI, it was discovered that you can add a chemical calledtetraethyl leadto gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs acatalytic converterand renders it inoperable within minutes.
TheEarthbecame covered in a thin layer of lead, andlead is toxicto many living things (including humans).

When lead was banned,gasoline got more expensivebecause refineries could not boost the octane ratings of cheaper grades any more.Airplanesare still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jet enginesburnkerosene, by the way).

另一个常见的添加剂MTBE。MTBE is the acronym formethyl tertiary butyl ether, a fairly simple molecule that is created from methanol.

MTBE gets added togasolinefor two reasons:

It boostsoctane.
It is anoxygenate, meaning that it adds oxygen to the reaction when it burns. Ideally, an oxygenate reduces the amount of unburned hydrocarbons and carbon monoxide in the exhaust.

MTBE started getting added to gasoline in a big way after the Clean Air Act of 1990 went into effect. Gasoline can contain as much as 10 percent to 15 percent MTBE.

The main problem with MTBE is that it is thought to becarcinogenicand it mixes easily with water. If gasoline containing MTBE leaks from an underground tank at a gas station, it can get into groundwater and contaminate wells. Of course, MTBE isn't the only thing getting into the groundwater when a tank leaks -- so is gasoline and a host of other gasoline additives.

According tothis page at the EPA:

Although there is no established drinking-water regulation, USEPA has issued a drinking-water advisory of 20 to 40 micrograms per liter (µg/L) on the basis of taste and odor thresholds. This advisory concentration is intended to provide a large margin of safety for noncancer effects and is in the range of margins typically provided for potential carcinogenic effects.

The most likely thing to replace MTBE in gasoline isethanol-- normal alcohol. It is somewhat more expensive than MTBE, but it is not acancerthreat.