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Green light for exhaust gas particle counting in German PTIs

PTB has published harmonized requirements for new, low-cost exhaust gas particle counters for mandatory vehicle inspections

press release

Improved air quality in city centers and climate protection – counting soot particles is to become an integral part of the exhaust examination of diesel cars within the scope of mandatory vehicle inspections in Germany (HU/AU). This novel task requires an entirely new type of measuring instruments that must first be developed and type-approved in order to be installed in vehicle workshops. To ensure uniform instrument quality, the Physikalisch-Technische Bundesanstalt (PTB) has drawn up metrological requirements for the required type certification of such particle counters in cooperation with the bodies concerned; these requirements were published last week. Manufacturers of such exhaust particle counters can now retrofit their instrument prototypes to meet the PTB requirements. Workshop owners offering mandatory, bi-annual vehicle emission tests (AU) can ensure that they are equipped with such instruments before 1 January 2023 – the date on which the requirements will go into force. And in Europe, Germany's neighboring countries now have a blueprint for developing similar solutions of their own. Based on this blueprint, the EU could even develop a harmonized European vehicle emission test that is similar to the already harmonized type approval of motor vehicles.

For the exhaust examination of Euro 6/IV diesel vehicles, counting particles in diesel exhaust gas will become mandatory as of 2023. Vehicle workshops must prepare for this new type of examination. Photo: Matt Boitor / Unsplash (royalty free)

Based on the particle number density in diesel exhaust gas, it will be possible to check whether the particle filter of a car is still in working order, and if so, how well it works. The exhaust gas limit value will be 250 000 particles per cm3. German lawmakers had originally planned for soot particle counting in diesel exhaust gas to be included in the regular “HU/AU” exhaust examination as of this year, but the introduction of the procedure for Euro 6 diesel vehicles was postponed to January 2023. This will give instrument manufacturers, testing bodies, and workshops the time necessary to prepare for this entirely new task. AUPNAg (the national working group for the introduction of a particle-counting technique in German PTI emissions tests (AU) and general inspections (HU)) has jointly developed a set of requirements for the new exhaust gas particle counters with the relevant bodies and industry associations represented by it. These requirements were recently published by PTB (DOI 10.7795/510.20210623) and form the basis for the instrument type examinations performed on this completely new class of exhaust meters that are required for German PTI tests. The entities involved in the AUPNag include: the Federal Ministry of Transport and Digital Infrastructure, the Federal Ministry for Economic Affairs and Energy, the Federal Highway Research Institute (BAST), TÜV, Dekra, verification authorities, ASA, VDA, VDIK, ZDK, and PTB.

Particle measuring instruments have existed for many years. They are used, for instance, in atmospheric research, to measure aerosols and to verify emission limits within the scope of vehicle type approvals. However, the measurement results obtained by means of these instruments are often not metrologically traceable; for workshops, the costs of these highly specialized instruments are much too high for them to be used in PTI scenarios. The challenge PTB faced was to develop requirements that would make particle counters sufficiently accurate and reliable while also allowing such counters to remain affordable for workshops and to be much simpler to use and more robust than former laboratory instruments.

PTI measuring instruments for exhaust examinations fall under the Measures and Verification Act and require an instrument type examination issued by a conformity assessment body. Currently, the Conformity Assessment Body of PTB is the only entity to issue such certificates in Germany. In 2018, PTB therefore commissioned a 360 m2 building accommodating testing laboratories for exhaust gas analyzers and exhaust gas particle counters. The new 4.4-million-euro building accommodates two cutting-edge laboratories for opacity and exhaust gas meters, a novel calibration laboratory for exhaust particle counters and the German primary standard for particle counting. The need for a new building arose due to the requirements of the German exhaust examination directive being tightened at the end of 2017. The metrological basis for this directive had been in development since 2011 – partly within the scope of a European research program and partly using PTB's own funds. To meet the increasing demand for tests and calibrations, a second research building accommodating two labs for particle counting and two labs for measuring nitrogen oxides is currently being built; the start of operations is planned for the fall of 2021. Metrological research and development for reliably measuring the NOx content in vehicle exhaust gas is one of PTB's strategic topics.



  • Prof. Dr. rer. nat. Volker Ebert, Head of Department 3.4, Analytical Chemistry of the Gas Phase, phone: +49 531 592-3401, email: Opens local program for sending emailvolker.ebert(at)ptb.de
  • Dr.-Ing. Sonja Pratzler, Conformity Assessment of Exhaust Meters, phone: +49 531 592-3215, email: Opens local program for sending emailsonja.pratzler(at)ptb.de


PTB Requirement “Particle Counters”

PTB Requirements 12.16, “Particle Counters”, DOI 10.7795/510.20210623, as of May 2021