Metrological traceability in particle measurements for national periodic technical inspections: uncertainty and influencing variables

Measurement of the particle number concentration in diesel exhaust has been mandatory for EUR 6/VI motor vehicles since July 2023. Even before this new measurand was introduced, PTB was already intensively involved in the realization and traceability of particle counting and contributed to the development of the infrastructure in Germany. The metrological traceability chain from results measured by instruments in the workshops via standards of the accredited laboratories to the national standard of PTB comprises different measurement techniques and calibration procedures. While the measurement uncertainty of the national standards is primarily determined by the realization of the SI units, other influencing factors such as the particle size, stability of the particle source or the calibration procedure are decisive at the end user level. In this article, we describe the metrological traceability and measurement uncertainties related to PTB’s service on “Type examination of particle counters in vehicle exhaust emission testing” and discuss the sources of uncertainty in the context of the internationally accepted calibration and measurement capabilities for aerosol particle measurements.