Significant amounts of particle-phase organic compounds are present in the exhaust of diesel vehicles. It is believed that some of these compounds have a greater impact on human health and the environment than other compounds. Therefore, it is of significant importance to speciate particle-phase organic compounds of diesel particulate matter (PM) to clarify the effects of PM on human health and the environment, and to understand the mechanisms of organic compounds formation in PM.
A dilution source sampling system was incorporated into the exhaust measurement system of a single-cylinder heavy-duty direct-injection (D.I.) diesel engine. This system was designed specifically to collect fine organic aerosols from diesel exhaust. The detailed system is described in Kweon et al. [27].
Samples were collected on a series of quartz fiber filters and analyzed by gas chromatography/mass spectrometry (GC/MS) techniques to quantify particle-phase organic compounds for various engine-operating conditions. The Cummins N14-series single-cylinder research engine was run under the California Air Resources Board (CARB) 8-mode test cycle. Thirty nine particle-phase organic compounds were quantified with high resolution particularly for light and medium load conditions. At the high load conditions, most of the particle-phase organic compounds were below detection limit of the GC/MS.
Results show that detailed organic chemical composition of PM is significantly affected by the change in the engine load and speed. Most of the organic compounds were observed at idling, light, and medium load conditions. The n-alkanes and PAHs comprised between 68 and 83% of the total identified particle-phase organic compounds with the n-alkanes between 39 and 44% and the PAHs between 28.5 and 39.3% for the conditions except the mode 2, in which the concentrations of the particle-phase organic compounds were above detection limits. The hydrocarbon distribution shows that the fractions of carbon numbers in PM varied significantly, particularly those with carbon numbers below 20 and between 25 and 30. Carbon numbers between 25 and 30 comprised a significant portion in the hydrocarbon distributions at light load and idling conditions. However, the fraction of the carbon number of less than 20 increased tremendously at higher loads. Carbon numbers of larger than 30 remained without significant change.