Impacts of Exhaust Transfer System Contamination on Particulate Matter Measurements

As the measurement of low levels of particulate matter (PM) and solid particulate number (PN) from light-duty vehicles becomes more critical, it is becoming more important to understand the potential impacts of exhaust transfer system contamination. This phenomenon occurs when, as it relates to vehicle emission testing, particles deposit and semi-volatile materials are adsorb onto the inner surfaces of the exhaust transfer system, which includes the vehicle exhaust pipe, the exhaust transfer line, and the constant volume sampling (CVS) system, and may subsequently re-entrain and desorb in subsequent vehicle tests. A soot loading cycle was successfully developed and resulted in 36 to 8600 mg of PM mass passing through the CVS tunnel. The results from cleaning tests suggested that majority of particles released during the cleaning tests are semi-volatiles with little presence of soot. A series of chassis dynamometer tests were conducted to characterize the differences between “clean” and “contaminated” sampling system and their impact on low level PM measurements. The results from this study show no measurable PM mass impacts between the “dirty” and clean tunnel conditions that were observed until after a high emitter was tested (80–120 mg/mi diesel vehicle).