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Appendix C: Tailpipe Emissions of Biodiesel

Biodiesel is promoted as a fuel that has significant greenhouse benefits, but the air quality benefits are not as clear.

Similar to the biofuels/greenhouse gas debate, there is research which seeks to determine the life-cycle emissions of biofuels. These studies examine both the upstream and downstream emissions resulting from the manufacturing and combustion of alterative fuels. This paper focuses on the tailpipe emissions only, and is intended to determine the impact of large-scale alternative fuel use in populated areas around New Zealand. This is a valid assumption especially as the vast majority of the health effects experienced from motor vehicle emissions occur in populated areas.

Even without full scale life cycle analysis there is a high degree of variability in the results of studies of tailpipe emissions. Part of this variability is due to factors such as engine temperature, driving and/or testing conditions, type of vehicle, age of vehicle, and type of biofuel (ie, feedstock). Two studies are summarised (Table C1).

Table C1: Studies on the air quality befits of biodiesel

Study details


Effect on emissions

Relevant information

1 EPA – A comprehensive analysis of biodiesel impacts on exhaust emissions (2002)


Use of B20 would result in a 10.1% reduction in PM for the heavy duty vehicle emissions on highways

Heavy duty (highway) vehicles only. A review of 80 studies was conducted – 39 of which were selected and included. Primarily based on pre-1997 engines.

2 Newcastle City Council Biodiesel Trial: Emissions Testing Program

Newcastle, Australia

Use of B20 resulted in a 39% reduction in PM emissions

The 12 vehicles tested including light duty four-wheel drives, light and medium duty trucks and garbage collection vehicles.

Further summary details on these studies are available from the authors upon request.