synthesis gas to methanol and use methanol-to-gasoline technology to produce gasoline, which fits directly into the existing U.S. fuel-delivery infrastructure. Hydrogen has the potential to reduce U.S. greenhouse gas emissions and oil use, as discussed in two National Research Council reports, Transitions to Alternative Transportation Technologies—A Focus on Hydrogen (NRC, 2008) and The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs (NRC, 2004). It is a long-term option, nonetheless.

Compressed Natural Gas

In 2007, the main uses for natural gas in the United States were electric power generation (30 percent) and industrial (29 percent), residential (20 percent), and commercial (13 percent) use. Only 0.1 percent was used in vehicles (EIA, 2008a). But natural gas is the cleanest and most efficient hydrocarbon fuel—it is environmentally superior to coal for electric power generation—and for similar reasons it could be a sound choice for transportation fuels.

Natural gas consumption levels in 2008 were satisfied mainly by domestic production (Chapter 7 on fossil fuels includes estimates of U.S. natural gas resources). However, a switch to natural gas for a large segment of U.S. transportation use would most likely trigger its increased importation. Even if natural gas were to be used for transportation rather than electricity generation, there is a potential to supply only about one-fifth to one-fourth of U.S. transportation needs from North American natural gas reserves, and only with investment in the distribution infrastructure. In any case, the technologies for producing transportation fuels from natural gas will be ready for deployment by 2020.

In 2008, there were more than 150,000 natural gas vehicles (NGVs) and 1,500 NGV fueling stations in the United States. Natural gas is sold in gasoline-equivalent gallons; each gasoline-equivalent gallon of natural gas has the same energy content (124,800 Btu) as a gallon of gasoline. NGVs are more expensive to purchase than are hybrid or gasoline vehicles. The Civic GX NGV has a manufacturer’s suggested retail price of $24,590, compared to $22,600 for the company’s hybrid sedan and $15,010 for its regular sedan (Rock, 2008).

Of all the fossil fuels, natural gas produces the least amount of CO2 when burned because it contains the lowest carbon-to-hydrogen ratio. It also releases lesser amounts of criteria air pollutants. NGVs emit unburned methane, which has a higher greenhouse forcing potential than does CO2, but this might be offset by the substantial reduction in CO2 emissions. When compared with gasoline-



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