I spoke with Nigel Clark about a study we recently completed, “Effects of Ethanol Blends on Light-Duty Vehicle Emissions: A Critical Review” with colleagues Terry Higgins and David McKain. The Urban Air Initiative supported the study, which was conducted independently.

We covered several points, including the following:

• Measured and modeled effects of ethanol blending on gaseous and particulate emissions have varied widely between studies, to the point that it is difficult to reach any summary conclusions on ethanol’s emissions effects. Why? For one thing, automotive technology is evolving, especially with the advent of the GDI engine. Vehicles may interact with specific fuels and test cycles in different ways, leading to inconsistent results.

• Another major issue this report discusses in depth is the fuel itself. The blending of fuels used in the studies reviewed represents a major cause of differences in conclusions and draws into question applicability to real-world predictions.

• Many of the blends used in emissions studies do not reflect typical makeup of in- use fuels. They are not reflective of real-world fuel blending that happens at the refinery or terminal. This is certainly the case in studies where “match blended” fuels were used to test a few select parameters, such as ethanol.

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