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Modern diesel aftertreatment systems may produce ammonia (NH3), especially in gas samples from midbed locations. NH3 causes significant measurement errors in NO, NO2, and NOx measurements for several NOx measurement technologies. A standard addition test was run adding NO, NO2, and/or NH3 to a diesel engine exhaust. Chemiluminescent (CLD), FTIR, and chemical ionization mass spectrometer (CIMS) instruments were used in a designed experiment. None of the instruments gave accurate, robust NOx measurement in the presence of high levels of NH3.

A commercial PEMS, the SemtechD, was evaluated for its suitability to measure transient emissions from light-duty, oxidation catalyst equipped, diesel passenger cars. The PEMS was evaluated for its analytical capabilities in a state-of-the-art chassis dynamometer test facility. The system, manufactured by Sensors, Inc of Saline, MI, proved to be both accurate and precise. The SemtechD proved capable of measuring THC concentrations (FID-based measurement) as low as 2 ppmC with measurements on average within 4.5% of those reported by modal test cell instrumentation. Similarly, both CO and NOx measurements fell within 9% and 3% of the values reported (respectively) by modal test cell analyzers. Finally, modal CO2 agreed within 2.6% of the two measurement systems across eleven vehicle tests and with more than 6000 data points compared.