Phase-based TEOM Measurements Compared with Traditional Filters for Diesel PM

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. At the 50-mg/mile level of the diesel vehicle used in the study, the TEOM results were on the average 10-15% lower than those from traditional particulate filter weighing. Use of the TEOM appears possible if the systematic offset can be identified and removed. A parallel portion of the study also compared two types of traditional filter - TX40 and T60A20 - and showed that they gave statistically identical results at the PM levels tested.