Ethanol is among the most widely used fuel alternatives in the world. It is so widely used, motorists would have to go out of their way to find gasoline that was not enriched with some amount of ethanol. In the United States alone, ethanol accounted for 9% of total gas sales in 2011. Many hail ethanol as a unique, eco-friendly alternative to using gasoline or diesel fuels. However, there is not universal agreement on the impact that ethanol emissions have on climate change and air quality.
Types of Ethanol Emissions
Ethanol emissions can be classified in two distinctive ways: production emissions and end-use emissions. Given the unique nature of how ethanol is produced and used, it makes sense to look at both sides of this coin when talking about ethanol emissions.
These emissions are sometimes referred to as "indirect" and result from the emissions generated by the production of ethanol fuel crops. The majority of ethanol used in fuels is known as cellulosic ethanol. This is ethanol that is produced by fermenting dedicated fuel crop varieties of corn, switchgrass, and sugar cane. While these crops are being produced, fossil fuels like gasoline and diesel are used in trucks, tractors, and warehouses to produce the crops.
When ethanol combusts, it releases primarily carbon dioxide and water vapor. Despite the fact that a gallon of ethanol produces less carbon dioxide than gasoline, it still produces greenhouse emissions like carbon dioxide. However, the combustion of ethanol is largely particulate-free, whereas gasoline combustion forces many particles into the air. Since a gallon of ethanol contains less energy than a gallon of gasoline, it can require more ethanol than gasoline to travel similar distances, which can contribute to greenhouse gas emissions.
Ethanol Emissions vs. Gasoline and Diesel
When looked at on a purely real-world, current, at-the-tailpipe emissions level, ethanol does reduce the overall amount of emissions coming out of a car tailpipe for each mile it is used.
A gallon of fossil fuels with release roughly 19.64 pounds of carbon dioxide into the atmosphere. By comparison, an 80/10 blend of fossil fuel and ethanol will emit 17.68 pounds of carbon dioxide.
A blend of 10% ethanol and gasoline can reduce the carbon monoxide load of gasoline emissions by 30%.
Volatile Organic Compounds
A blend of 10% ethanol and gasoline can reduce the amount of volatile organic compounds in the exhaust by 7%.
Environmental Impact of Emissions
The impact of ethanol on the environment is much lower than gasoline or diesel. However, there are still a few environmental impacts from ethanol emissions that should be considered.
- When the emissions from the production of ethanol crops are added to the emissions from combustion, many argue that the use of ethanol can actually create more greenhouse gasses like carbon dioxide.
- Volatile organic compounds are a result of the distilling, fermentation, and drying process in the production of ethanol. These compounds get into the air and can lead to negative health impacts.
- While the combustion of ethanol creates much lower levels of noxious chemicals, the plants that produce the ethanol do produce high levels of carbon dioxide and nitrogen emissions.
Putting It All Together
The debate over the viability of ethanol as a fuel source is far from over. In fact, the issue is much more complex than simply looking at the ethanol itself. Everything from where the ethanol is produced to what plant the ethanol was derived from can have a major impact on overall ethanol emissions. The truth is that there is no question over whether ethanol blended fuels produce lower amounts of greenhouse gasses. The argument lies in the more holistic approach that takes both production and use of ethanol as a fuel into account when calculating total emissions.