Time resolved characterization of diesel particulate emissions. 1. Instruments for particle mass measurements

The measurement of diesel vehicle exhaust particulate mass is currently acc omplished using filter collection methods according to the Code of Federal Regulations (CFR). Such filter methods limit time resolution to a minimum o f several minutes, making it impossible to study emissions during transient operating conditions. Extensive testing of five different measurement meth ods has demonstrated that fast response measurements of diesel exhaust part iculate mass concentrations, consistent with CFR filter measurements, are f easible using existing technology. The measurement principles of choice are the real time weighing of exhaust samples as implemented in the tapered el ement oscillating microbalance (TEOM) and the measurement of lightscatterin g from exhaust particles as implemented in the DustTrak nephelometer. Each of these two instruments has distinctive strengths. The TEOM excels in the area of constant calibration, independent of vehicle. For the DustTrak, thi s calibration varies by vehicle. On the other hand, the DustTrak has an exc ellent signal-to-noise ratio, freedom from interference due to other exhaus t sample properties, good time resolution, and simplicity. The strengths of the two measurement methods are complimentary, so an obvious suggestion is to integrate them. The nephelometer would obtain a fast response signal, w ith near real time calibration provided by the microbalance.