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A direct comparison is made of time-resolved measurements of diesel PM emissions obtained using laser-induced incandescence (LII), an electrical low pressure impactor (ELPI), and a tapered element oscillating microbalance (TEOM). The measurements were made on two diesel passenger vehicles, one of which was equipped with a diesel particulate filter. Both LII and the ELPI performed well for both vehicles, whereas the TEOM lacked the sensitivity required for the filtered vehicle. We estimate that the LII system used has a limit of detection better than 0.2 mg/mi.

Collection of diesel exhaust using the Tapered Element Oscillating Microbalance (TEOM) instrument was investigated as an alternative to the traditional method of filter weighing for particulate matter mass determination. Such an approach, if successful, would eliminate considerable manual labor involved in weighing, as well as the delay of hours or days before final results were known. To avoid known artifacts in the second-by-second mode of operation, the TEOM was used in a phase-by-phase mode and was equilibrated with air of constant temperature and humidity before each measurement. Electrically operated valves were used to automate the equilibration and measurement process. The study also included a comparison between two types of TEOM filter - an older type and a new one designed by the TEOM manufacturer for more uniform flow and less flexing. Best results were obtained with the TEOM using the new filter under no-flow conditions.

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. Static charge that builds on filters from handling can dramatically influence the measurement results, especially at low PM levels such as those produced when testing typical gasoline-powered vehicles or diesel-powered vehicles employing DPF (Diesel Particulate Filter) technology. It was found that proper grounding of equipment, furniture, and floor was insufficient to mitigate the effects of static electricity when using the traditional method of weighing from a glass Petri dish in the presence of an ionizing bar. A stainless steel EDP (Electrostatic Discharge Platform), using commercially available ionizing bars, was developed and proven to successfully reduce filter measurement variability when weighing PTFE membrane filters on a 0.1 microgram balance.