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.