Second Generation TEOM Filters-Diesel Particulate Mass Comparisons between TEOM and Conventional Filtration Techniques

A tapered element oscillating microbalance (TEOM), using second generation diesel particulate filters, was subjected to calibration and response testing, and was also used in direct comparison tests with conventional filtration techniques. Non-volatile masses placed on the TEOM filter demonstrated a 1:1 correspondence between TEOM mass response and gravimetric mass determinations. The TEOM mass response to dilute diesel exhaust particulate for a vehicle at idle was typically 23% lower than conventional filtration gravimetric results when both TEOM and conventional filters collected particulate at the same temperature and on the same filter media type. The effects of varying filter temperature and particulate extractable content were consistent with the premise that the retention of volatile species on the TEOM filter was lower than on conventional filters due to the relatively high TEOM vacuum downstream of the TEOM filter. Differences in mass determinations were, therefore, attributed primarily to differences in volatile species retained by the filter-particulate matrix. TEOM measurements are suggested to be equivalent to conventional filtration mass determinations at filter temperatures several degrees higher than TEOM filter temperatures.