What is biodiesel?
Biodiesel is a fuel derived from vegetable oil or animal fats that can be an additive to or entirely replace conventional petroleum diesel fuel. In the United States, the majority of biodiesel is made from soybean or canola oils, but is also made from waste stream sources such as used cooking oils or animal fats.

What is a biodiesel blend?
In most cases, biodiesel is mixed with conventional diesel because of the higher cost of biodiesel, engine compatibility issues, and cold weather operating concerns. Common blends are B20, or 20% biodiesel and B2, or 2% biodiesel. The environmental benefits of using biodiesel scales with the percent of biodiesel contained in the blend.
• B100 – 100% biodiesel offers the most overall environmental benefits. Use of B100 may require engine or fuel system component modification and can cause operating problems, especially in cold weather.
• B20 – 20% biodiesel offers about one fifth of the environmental benefits of B100, but can be more broadly applied to existing engines with little or no modification.
• B2 – 2% biodiesel offers little environmental or petroleum dependence benefit and could be potentially used an environmental marketing tool.

What are the main issues when switching from conventional diesel to biodiesel?
The main operating issues are cold weather operability, engine and fuel system compatibility, and the solvency properties of biodiesel. B100 does not flow as well as petroleum diesel in cold temperatures, and requires special additives or fuel heating systems to operate in colder climates. B100 may cause rubber seals and gaskets from engines older than 1994 to wear faster or fail. Biodiesel also acts as a solvent, which can dissolve sediments in diesel fuel tanks and clog fuel filters during an initial transition from petroleum diesel. Despite these issues, some fleets are successfully using B100. Berkeley, California is successfully running 100% biodiesel in 90% of their public diesel fleet vehicles including fire trucks.1 Using B20 minimizes or eliminates most of the concerns with B100 and is therefore more widely used.

Does using biodiesel in place of conventional diesel help combat global climate change?
Plant-based B100 resulted in over 75% less carbon dioxide emissions than conventional diesel in a full lifecycle assessment.2 Although tailpipe carbon dioxide (CO2) emissions are similar for diesel and biodiesel operated engines, biodiesel provides a distinct advantage in a full lifecycle assessment in which emissions from fuel production and fuel use are considered. In the case of plant-based biodiesel, carbon dioxide uptake by plants during respiration offsets the CO2 emissions produced from the combustion of biodiesel.

What are the tailpipe emissions impacts from using biodiesel?
Replacing conventional diesel with B100 reduces most tailpipe emission pollutants, but increases emissions of nitrogen oxides.
SMOG: B100 results in large reductions in hydrocarbons (HC) but about a 10% increase in nitrogen oxide (NOx) emissions, resulting in a small overall increase of smog forming pollutants. These pollutants are responsible for the urban smog that reduces lung function, increases incidents of asthma and can aggravate chronic lung disease. Increases in NOx emissions could be minimized through engine modifications, fuel additives, or exhaust after-treatment devices. Although tailpipe HC emissions are reduced, in a full lifecycle assessment, smog forming HC emissions were 35% higher than conventional diesel. The emissions are attributed to the farming and soy processing components of biodiesel production.
Soot
B100 has shown about a 50% reduction in particulate matter (PM or soot) emissions. Diesel PM has been shown to exacerbate respiratory conditions and cause premature death.
Air Toxics
Other emissions benefits of B100 include a reduction in air toxics on the order of 60-90%.3 Air toxics, such as formaldehyde and benzene, can cause a variety health risks including cancer, immune system disorders and reproductive problems.

Are there other environmental attributes of biodiesel?
Biodiesel is non-toxic and biodegrades four times faster than conventional diesel. Biodiesel therefore presents a much smaller risk in the case of spills in marine and other sensitive environments.
Production of biodiesel creates approximately 95% less hazardous waste than petroleum diesel production but more than double the amount of non-hazardous waste. Hazardous waste generally comes from chemical products associated with petroleum refining. The majority of non-hazardous waste from biodiesel is attributed to unprocessed plant material from the soybean crushing stage.
Large volume biodiesel use could raise concerns about genetically modified crops, pesticide use, and land-use impacts common to all plant-based fuels. Since biodiesel is made from plant-based oils or waste stream sources, it is considered a renewable fuel. However, waste vegetable and animal fat resources are estimated to be able to sustain production on the order of 1 billion gallons of biodiesel per year, or less than 3% of current diesel use.4 Widespread use of biodiesel would require more virgin plant oils or other waste stream sources to meet larger demands. Crops for biodiesel must be grown in a manner that supports wildlife habitat, minimizes soil erosion, avoids competition for food crops, and does not rely on the use of harsh chemicals and fertilizers.

How much does it cost?
Prices for B100 can be twice as high as conventional diesel, while lower biodiesel blends show more modest increases. The pump price for biodiesel varies regionally and depends both on the source of the fuel and the percent blend with conventional diesel.5

What is the future outlook for biodiesel?
Biodiesel is one of the many alternative fuel options that can help reduce oil dependence and global warming pollution. Using high percentage blends of biodiesel in an existing diesel vehicle offers clear green-house-gas benefits and reductions in most criteria air pollutants and air toxics compared with petroleum based diesel. In addition, it is a renewable fuel that is produced from domestic resources. Using B20 in all highway diesel engines would reduce highway petroleum fuel use less than 5%.6 To make a significant impact on petroleum use and global warming emissions biodiesel needs to be used in higher blends.