Evaluation of N2O Measurement Instrument with Light-Duty Vehicles.

摘要

The program objective was to examine a variety of commercially-available instruments for the laboratory measurement of nitrous oxide (N2O) on light-duty vehicles. Four different instrument technologies capable of sampling dilute bag exhaust samples were compared in this study to results obtained on a benchmark instrument. The benchmark instrument used as a reference for N2O levels during this program was a gas chromatograph instrument which incorporated an electron capture detector (GC-ECD). The instruments were evaluated using diluted bagged exhaust samples generated from two light-duty vehicles operating over the chassis dynamometer portion of the Federal Test Procedure (FTP). The two vehicles were a Nissan Altima and a Toyota Camry. The variability of the instruments is relatively high compared to the reference. A comparison of all instrument percent differences with respect to the GC-ECD within each Camry test shows a best agreement of 7% and worst agreement of 81%. The Altima showed a best agreement of 12% and worst agreement of 51% within each Altima test. However, given the low N2O emission rate average of 2.5 mg/mi for these two vehicles, the worst case agreement of 81% gives a spread of 0.5 mg/mi to 4.5 mg/mi. This is still less than the current 10 mg/mi N2O standard. A review of late model vehicles with direct injection technology shows similar or lower N2O emission rates. Nevertheless, the observed variability of the instruments would make it difficult to accurately measure N2O levels from vehicles closer to the N2O standard.