Another look at fuel-cell cars.

E's answer to the reader's question on water vapor exhaust from fuel-cell cars missed some key points (Earth Talk, March/April 2005). It is true that gasoline-fueled vehicles emit a lot of carbon dioxide (CO2). According to the Natural Resources Defense Council, an automobile engine produces 20 pounds of CO2 for every gallon of gas it burns, or about one pound per mile. But gasoline combustion also results in over a pound of water for every pound of fuel burned. So, we are already getting water vapor from our fuel. Since CO2 is a stronger greenhouse gas and has more impact on climate than water, water isn't usually mentioned as a problem.

The real problem with hydrogen fuel is not so much the water produced (4.5 pounds for each pound of hydrogen) as it is the carbon. Hydrogen is not a "free" gas--it has to be produced. The most likely methods are electrolysis or production from fossil fuels, such as natural gas or fuel oil. If electrolysis is used, it will most likely be by way of nuclear power plants, which means more of those will have to be built, or by coal-fired plants, which means lots of CO2 will be released. If hydrogen is generated directly from fossil fuels, then the carbon problem remains similar to what we see with burning gasoline, unless some CO2 scrubbers are used.

Dick Lawrence

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