According to the U.S. Environmental Protection Agency, using pure biodiesel (B100) instead of conventional diesel reduces these emissions:

  • Hydrocarbons by more than 60 percent
  • Carbon monoxide by more than 40 percent
  • Particulates by more than 40 percent

EPA studies also suggest that using biodiesel reduces the numerous toxic substances present in diesel exhaust (including many cancer-causing compounds).

Biodiesel also presents fewer health risks during storage and handling. The fuel is 100 percent biodegradable if spilled and has roughly the same toxicity as table salt, making it especially attractive for use in sensitive natural environments.

> Read an overview of biodiesel as a fuel choice

Antidote to Global Warming?

Biodiesel can have favorable effects on climate change emissions, although there is some debate about the net amount of greenhouse gases released in biodiesel production and use.

Advocates claim that biodiesel is carbon-neutral; that is, that the amount of carbon dioxide (a key greenhouse gas) absorbed by the feedstock plants is equal to the amount later emitted by vehicles using the fuel. The feedstock crops used to make biodiesel, such as soybeans, absorb carbon dioxide while they are growing, removing the gas from the atmosphere. Later, the carbon dioxide is put back when vehicles burn the fuel. It’s like an eco-system on wheels.

The U.S. Department of Energy concludes that, relative to conventional diesel fuel, biodiesel decreases carbon dioxide output by 78.5 percent.

Some say that biodiesel’s carbon-neutral claims are optimistic, mainly because of the energy-intensive nature of modern farming and fuel production. Greenhouse gases are emitted throughout the process of oil feedstock production from sources such as farm machinery, trucks that transport the crops to processing facilities, and power plants that supply electricity for the production process.

School of Hard NOx

Greenhouse gas emissions can vary significantly depending on the feedstock. The same holds true for emissions of NOx, a key component in smog formation. A study at the University of California–Davis suggests that biodiesel made from new soybean oil actually may be more harmful to the climate than conventional petroleum-based diesel because the cultivation of soybeans results in the emissions of NOx.

In fact, EPA tests show that using B100 instead of conventional diesel results in 10 percent higher emissions of oxides of nitrogen. It’s important to note that more NOx doesn’t always result in more smog: smog formation is also affected by the amount of sunlight as well as the presence of other pollutants including reactive organic compounds. But as more cities struggle with air quality issues, they have increasingly focused on lowering NOx as a way to combat higher levels of smog. Future diesel engine emission controls may address the NOx problem, but there’s no way around it: biodiesel contributes disproportionately to the NOx problem and, under some conditions, to more smog.

All vehicles represent a set of compromises. Biodiesel vehicles are no different: less dependence on petroleum, fewer climate change emissions, better general air quality—but contribute a bit more to smog. You choose your battles.