Research Projects

Project at a Glance

Project Status: complete

Report Published 2001:

Title: Refinement of selected fuel-cycle emissions analyses

Principal Investigator / Author(s): Unnasch, Stefan

Contract Number: 98-338

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


Emissions associated with the production and distribution of fuels can be significant in comparison with tailpipe and exhaust emissions. Examining these fuel-cycle emissions for alternative-fueled vehicles appears relevant when assessing the overall environmental impact of these vehicles from both a global and local perspective.

This study determines oxides of nitrogen (NOx), non-methane organic gases (NMOG), toxics, carbon monoxide (CO), and carbon dioxide (CO2) emissions for methanol, diesel, LPG, and electric vehicle operation. Reformulated diesel and synthetic diesel were also analyzed. These fuel options are of interest because they potentially result in relatively low refueling emissions. The purpose of the study is to investigate those fuels that might be categorized as having low fuel cycle emissions. Vehicles operating on 100 percent methanol, LPG, and diesel were judged by ARB to result in fuel-cycle NMOG emissions that are close to 0.01 g/mi. Fuels with clearly lower fuel cycle emissions such as CNG and hydrogen are not analyzed in this study. Gasoline was also not analyzed as the results of a 1996 fuel-cycle study indicated NMOG emissions around 0.03 g/mi (Unnasch 1996). These results do not reflect improvements that could be achieved with advanced gasoline hybrid vehicle technologies and further investigation is warranted.

Emissions considered in this study are those associated with the operation of extraction, production, and distribution equipment. Emissions associated with the production or decommissioning of facilities or vehicles are not evaluated. Emission calculations are based on vehicle operation in the South Coast Air Basin and the fuel-cycle emissions are allocated according to where they occur including a summation of emissions within only the South Coast Air Basin.

Fuel-cycle emissions vary substantially based on factors such as the time-frame under consideration, vehicle fuel economy, the degree of emission control, amount of fuel produced and processed within the South Coast Air Basin, and assumptions regarding feedstock sources. Another important consideration is whether average emissions for all fuel production or marginal emissions for the production of the last unit of fuel are of interest. This study considers marginal emissions in the late 1990s and 2010 time frames.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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