Ethanol driven cars produce more ozone than gasoline driven cars

The researchers found that the ozone concentration of cars using ethanol was higher than that of cars using gasoline, especially in winter. This may cause new health problems in areas where ozone was not serious before.

According to a new study led by researchers at Stanford University, ethanol - usually promoted as a clean burning renewable fuel that can help the United States get rid of its dependence on oil - may worsen the health problems caused by ozone more seriously than gasoline, especially in winter.

The ozone generated by gasoline and E85 (a mixture of gasoline and ethanol, containing 85% ethanol) is more in warm sunshine than in cold weather and short winter, because heat and sunlight contribute to the formation of ozone. However, E85 produces different combustion by-products from gasoline, and produces more aldehyde, which is the precursor of ozone.

Diana Ginnebaugh, a doctoral candidate in civil and environmental engineering who participated in the study, said: "We found that at warmer temperatures, when E85 was used, the ozone content was slightly higher than that of gasoline." She will announce her research results at the American Geophysical Union meeting in San Francisco on December 15 (Tuesday). "But even a slight increase is a problem, especially in places like Los Angeles. Because you have high ozone, you must worry about it, so you don't want any increase."

But in the low temperature below freezing point, E85 seems to have the strongest impact on health.

Ginnebaugh said: "We found that the amount of ozone produced by E85 at low temperatures was significantly increased compared with gasoline when only considering emissions and atmospheric chemistry." Although ozone is usually low in cold winter conditions, "if you change to E85, suddenly, places like Denver will exceed the limit of ozone's impact on health, and then they will have health problems that do not exist now."

The problem of exhaust emissions in cold weather is that the catalytic converter used in the vehicle must be preheated before reaching full efficiency. Therefore, before they become warm, a large part of pollutants will escape from the exhaust pipe to the air.

Burning E85 instead of gasoline will increase other pollutants in the atmosphere, some of which are irritating to eyes, throat and lungs, and will also damage crops. However, aldehyde is the largest contributor to ozone production and also carcinogenic.

Ginnebaugh worked with Mark Z. Jacobson, a professor of civil and environmental engineering, to use some vehicle emission data from early research and apply it to Los Angeles area to simulate the pollutants that may be generated by vehicles.

Since E85 is only used in mass production vehicles now, researchers predict that by 2020, more "flex fuel" vehicles using E85 may be put into use. They estimate that automobile emissions will be reduced by about 60% compared with the current level, because automobile technology may continue to become cleaner over time. They investigated two situations, one is that all vehicles use E85, the other is that all vehicles use gasoline.

They ran a widely used complex model, involving more than 13,000 chemical reactions, and simulated the two cases repeatedly at different ambient temperatures for 48 hours each time. They used average ozone concentrations over these periods to compare.

They found that in warm temperatures, from freezing point to 41 ℃ (F conversion), in bright sunlight, E85 makes the concentration of ozone in the air 7 billionths higher than gasoline. At low temperatures, from freezing point to minus 37 degrees Celsius, they found that E85 increased the ozone concentration by 39 parts per billion more than gasoline.

"Our view of these results is that you see growth," Ginnebaugh said "We do not mean that this is the exact degree you will get in a specific urban area, because it really varies from city to city, depending on many other factors, such as the number of natural vegetation, traffic levels and local weather patterns."

Ginnebaugh said that the results of this study represent a preliminary analysis of the impact of E85. She said that more research data on emissions of flex fuel vehicles at different temperatures would help improve estimates.