Making the switching from petrol to ethanol to run our cars has turned out to be trickier than originally thought.

First, there was the impact on food prices, as more corn was grown to fuel vehicles instead of people. And now, there’s another potential downside: increased ozone pollution, along with all the associated health problems that can cause.

While both regular gasoline and E85 — a 15 per cent petrol, 85 per cent ethanol blend — tend to promote ozone production during warm, sunny weather, researchers at Stanford University have found that burning ethanol creates a host of different byproducts than gasoline and generates substantially more aldehydes, which are precursors to ozone.

“What we found is that at the warmer temperatures, with E85, there is a slight increase in ozone compared to what gasoline would produce,” said Diana Ginnebaugh, a doctoral candidate in civil and environmental engineering who worked on the study. “But even a slight increase is a concern, especially in a place like Los Angeles, because you already have episodes of high ozone that you have to be concerned about, so you don’t want any increase.”

The ozone risks of ethanol becomes even greater at below-freezing temperatures, the study found.

“We found a pretty substantial increase in ozone production from E85 at cold temperatures, relative to gasoline when emissions and atmospheric chemistry alone were considered,” Ginnebaugh said. Although ozone is generally lower under cold-temperature winter conditions, “If you switched to E85, suddenly you could have a place like Denver exceeding ozone health-effects limits and then they would have a health concern that they don’t have now.”

The problem with cold weather emissions arises because the catalytic converters used on vehicles have to warm up before they reach full efficiency. So until they get warm, a larger proportion of pollutants escapes from the tailpipe into the air.

Burning E85 instead of petrol also produces many other pollutants. Some are irritants to eyes, throats and lungs, or can damage crops, but the aldehydes are the biggest contributors to ozone production, as well as being carcinogenic.

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