Final answer:
The blending of pure ethanol with fuels is mainly done to improve the combustion efficiency and reduce emissions. Though it reduces energy content, it is part of efforts to meet local market demands and environmental goals.
Step-by-step explanation:
The blending of pure ethanol with other fuels primarily aims to improve the combustion efficiency of the fuel, which in turn can reduce pollutant emissions. Ethanol, when added to gasoline to create mixtures like E10, E15, or E85, helps reduce dependence on conventional oil and has a high octane rating which allows it to burn more slowly. Ethanol does have a lower energy density than gasoline, meaning that it has less energy content; however, it can produce cleaner emissions, with lower carbon monoxide and carbon dioxide.
Furthermore, there are multiple factors, including political and environmental considerations, that influence the mandate to introduce ethanol into fuel blends. Ethanol production can affect land use due to the competition between fuel and food crop cultivation, and may be associated with an increase in certain air pollutants due to higher "evaporative emissions" from fuel tanks and dispensing equipment.
Biodiesel, another form of biofuel, can also be mixed with petroleum diesel and is made from various plant sources. It generally produces less sulfur oxides, particulate matter, carbon monoxide, and other hydrocarbons upon combustion but can increase nitrogen oxide emissions, in comparison to petroleum diesel. Overall, the blending operation's goal is to meet the specific requirements of the local market while balancing economical, political, and environmental factors.