Investigation of Nitro-Organic Compounds in Diesel Engine Exhaust: Final Report, February 2007 - April 2008

Abstract

Executive SummaryDiesel particle filters (DPF) dramatically reduce the level of particulate matter (PM) emitted by diesel engines. There has not, however, been much research to verify that unregulated organic pollutants associated with diesel PM are also reduced by the use of DPFs. The U.S. Department of Energy's National Renewable Energy Laboratory recently upgraded its ReFUEL engine and vehicle testing facility's capabilities to speciate unregulated gas-phase emissions. To complement this capability, the laboratory contracted with the Colorado School of Mines to study the effects of soy biodiesel fuel and a DPF on emissions of polycyclic aromatic hydrocarbons (PAH) and nitro-polycyclic aromatic hydrocarbons (NPAH). These are related types of harmful but unregulated emissions associated with PM from diesel engines.In this study, the Colorado School of Mines developed procedures to sample diesel PM emissions from raw and diluted exhaust, with and without a DPF. They also developed improved procedures for extracting PAH and NPAH from the PM and quantifying those compounds with a gas chromatograph-electron monochromator mass spectrometer. While the study found the DPF generally reduced PAH emissions by 1 to 3 orders of magnitude, PAH conversion was lowest in the case of B100, suggesting that PAHs were actually being formed in the DPF. This finding warrants further investigation.Orders of magnitude reductions were also generally found for NPAH emissions exiting the DPF. However, the conversion of 1-nitropyrene through the DPF was less than 50% for all fuels. Because 1-nitropyrene has been shown to be mutagenic and carcinogenic, and because the DPF may concentrate condensable organics on a larger number of smaller particles, this could be a very significant concern. Differences in NPAHs between raw and dilution-tunnel PM samples suggest that chemical reactions continue through the raw exhaust system or occur during dilution. The apparent net effect is to reduce the diversity of NPAH compounds and in particular increase the amount of 1-nitropyrene.iii