Analysis completed by the Environmental Protection Agency (EPA) in 2002 compiled the most robust data set on biodiesel tailpipe emissions from heavy-duty engines. The findings were published in A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions (PDF 765 KB), a report that analyzes data from 39 studies. Download Adobe Reader. It concludes that biodiesel decreases emissions of particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) commensurately with its blend level, as shown in the figure below.

Source: EPA 2002

Later studies show that biodiesel particulate matter (PM) emissions are not only reduced but are less toxic. These studies are analyzed in Impact of Biodiesel Fuels on Air Quality and Human Health (PDF 615 KB), which concluded that the PM from B100 (100% biodiesel) and B20 (20% biodiesel, 80% diesel) is 20% and 5%, respectively, less toxic than PM from diesel. Download Adobe Reader.

EPA’s study also found a slight increase in NOx emissions (2% for B20). However, Effects of Biodiesel Blends on Vehicle Emissions (PDF 1.8 MB), published by the National Renewable Energy Laboratory (NREL), presented data and analysis suggesting that B20 has no net impact on oxides of nitrogen (NOx) emissions. Download Adobe Reader. This study attributes EPA’s reported increase to a dataset that was not adequately representative of all on-highway engines. The following table combines EPA’s results with those of NREL.

These and nearly all other diesel and biodiesel emissions studies do not include evaporative emissions. This is because an inconsequential amount of these fuels evaporates due to their extremely low Reid vapor pressure.

Lifecycle Emissions and Petroleum Use

A lifecycle analysis completed by NREL found that carbon dioxide emissions for B100 were 78.5% less than those from petroleum diesel. It also showed that biodiesel reduces petroleum use by 95% throughout its lifecycle.