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E85 is a blend of 15% ethanol in gasoline, and is one of a number of options being considered for future fuels. Ethanol can be derived from a number of agricultural sources which take up CO₂ from the atmosphere as they grow, and when used as fuel they contribute less to net atmospheric CO₂ compared to gasoline.

Three-way catalysts provide a very efficient way of removing harmful emissions from gasoline vehicle exhausts, and are now fitted to all vehicles. They start to become effective within a few seconds after starting the engine, but in these few seconds trace amounts of emissions from the engine can reach the vehicle tailpipe.

The size of this “cold start” emission is carefully regulated and has been considerably reduced as emission control technology has developed.

Ethanol may be partially converted to aldehydes during the short cold start period, and these may pass through the catalyst for the few seconds it takes to reach catalyst operating temperature. Aldehydes have a much stronger odour than hydrocarbons formed from gasoline combustion. Emission control specialists are aware of this and are currently developing new technologies to reduce these very low emissions still further.

These new technologies work by trapping the aldehydes and other combustion products while the catalyst reaches operating temperature, and then releasing them after a short time to be removed by the catalyst in the normal way. The goal is to enable new lower carbon fuels to be used without any effect on the vehicle emissions.

Answer posted 09 May 2007