Leaking Methane from Natural Gas Vehicles: Implications for US Greenhouse Gas Reductions from the Automobile Sector

Victor, D.G. (1989). Leaking Methane from Natural Gas Vehicles: Implications for US Greenhouse Gas Reductions from the Automobile Sector. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-89-055

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Abstract

A model of the US automobile market is used to test the role that natural gas vehicles (NGVs) might play in reducing greenhouse gas emissions. Since natural gas (methane) emits less CO2 per unit of energy than petroleum products, NGVs are an obvious pathway to lower CO2 emissions. High and low demand scenarios are used to forecast the emissions from unrestricted growth and a modest program of conservation, respectively. Based on these scenarios, a reference scenario is developed that projects a possible future path of automobile use and efficiency. I find that without dramatic shifts in automobile use, fuel consumption and greenhouse gas emissions will probably decrease in the future, provided that efficiency continues to improve at modest rates. In theory, NGVs can help shift emissions even further down.

A second objective is to quantify the role that leaking natural gas (methane) might play in offsetting some of the greenhouse advantages of NGVs. A simple atmospheric chemistry model is applied to the reference case. Based on current estimated leakage rates of about 3.6%, nearly all the greenhouse advantages of NGVs are consumed by the greenhouse contribution from leaking methane.

If oil operations (used to supply gasoline to conventional vehicles) also yield natural gas leaks then the relative case for NGVs should be more favorable. Scenarios that account for this are also explored. However, it appears that even if this source of methane is included, NGVs do not have substantial advantage over oil-based automobile fuels for two reasons: 1) the CO2 advantage of natural gas (compared with oil) is compensated by the methane leakage, and 2) there are not large gains in efficiency from using natural gas instead of oil products in automobiles.

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