One of the aims of the Bioethanol for Sustainable Transport (BEST) project is to demonstrate the
environmental benefits of ethanol as an alternative to fossil-based transport fuels. The BEST
Evaluation Plan provides a systematic framework for monitoring and assessment of those benefits,
based on a detailed set of evaluation requirements for the demonstration activities in the project. These
requirements include monitoring of ethanol usage at the project sites, reviewing the available evidence
for the environmental impacts of ethanol use, and where necessary, carrying out new analyses to
improve our understanding of those impacts. This report is a review of the available evidence for the
air quality impacts of using ethanol fuels in transport. The report focuses on regulated and unregulated
air pollutant emissions from vehicles running on ethanol fuels, but does not cover greenhouse gas
emissions.
The review begins with a general overview of the air quality impacts of burning fuels in vehicle
engines, listing the types of pollutants normally produced and their impacts on human health and the
environment. The factors influencing air pollutant formation and standard methods of limiting
pollutant production and emission are described. The specific impacts of using ethanol in both petrol
and diesel engines are then considered, both from the perspective of what current knowledge indicates
those impacts should be, and through considering the reported results of recent studies.