Posted by: Pradeep | June 1, 2008

Biodiesel Emissions

Biodiesel is the first and only alternative fuel to have a complete evaluation of emission results and potential health effects submitted to the U.S. Environmental Protection Agency (EPA) under the Clean Air Act Section 211(b). These programs include the most stringent emissions testing protocols ever required by EPA for certification of fuels or fuel additives. The data gathered complete the most thorough inventory of the environmental and human health effects attributes that current technology will allow.

The ozone (smog) forming potential of biodiesel hydrocarbons is 50% less than diesel fuel.

Sulfur emissions are essentially eliminated with pure biodiesel. The exhaust emissions of sulfur oxides and sulfates (major components of acid rain) from biodiesel are essentially eliminated compared to diesel.
Criteria pollutants are reduced with biodiesel use. Tests show the use of biodiesel in diesel engines results in substantial reductions of unburned hydrocarbons, carbon monoxide, and particulate matter.

Emissions of nitrogen oxides stay the same or are slightly increased.

Carbon Monoxide – The exhaust emissions of carbon monoxide (a poisonous gas) from biodiesel are on average 48 percent lower than carbon monoxide emissions from diesel.

Particulate Matter – Breathing particulate has been shown to be a human health hazard. The exhaust emissions of particulate matter from biodiesel are about 47 percent lower than overall particulate matter emissions from diesel.
Hydrocarbons – The exhaust emissions of total hydrocarbons (a contributing factor in the localized formation of smog and ozone) are on average 67 percent lower for biodiesel than diesel fuel. Nitrogen

Oxides – NOx emissions from biodiesel increase or decrease depending on the engine family and testing procedures. NOx emissions (a contributing factor in the localized formation of smog and ozone) from pure (100%) biodiesel increase on average by 10 percent. However, biodiesel’s lack of sulfur allows the use of NOx control technologies that cannot be used with conventional diesel.

Biodiesel reduces the health risks associated with petroleum diesel. Biodiesel emissions show decreased levels of polycyclic aromatic hydrocarbons (PAH) and nitrated polycyclic aromatic hydrocarbons (nPAH), which have been identified as potential cancer causing compounds. In Health Effects testing, PAH compounds were reduced by 75 to 85 percent, with the exception of benzo(a)anthracene, which was reduced by roughly 50 percent. Targeted nPAH compounds were also reduced dramatically with biodiesel, with 2-nitrofluorene and 1-nitropyrene reduced by 90 percent, and the rest of the nPAH compounds reduced to only trace levels.



  1. Although biodiesel does not show unsubstituted PAHs or nitro-PAHs to much of a level, I think nobody has looked for oxygen-derivative PAHs. These have not been looked for because the combustion zone has been low in available oxygen atoms. For conventional diesel the level of O-PAHs is very low.

    Why are O-PAHs important. The body metabolized PAHs to various O-PAHs – hydroxyl, epoxide, keto, aldehyde and other compound types. These are the actual active mutagens that bind to DNA and cause cancer and birth defects.

    Diesel combustion is very complex and many reactions can occur. There are thousands of molecules produced when biodiesel is combusted. I think a potential risk should be assessed before biodiesel is given a clean label.

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