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Periodic technical inspection for diesel soot emissions

In order to check the exhaust gases of road vehicles regularly, researchers from the FHNW have developed a portable measuring device .


Starting situation

With the introduction of particulate filters, particulate emissions from internal combustion engines fell very sharply. A good filter has an efficiency of well over 99%. Often the concentration in the exhaust gas is then lower than in the ambient air. At about the same time, various on-board diagnostic systems were introduced. In the opinion that these would detect a malfunction of the exhaust gas purification systems, the exhaust gas test was abolished.

Meanwhile, it is becoming increasingly clear that while emissions are very low when filters are intact, a small percentage of filters are either defective or have been tampered with, or even removed altogether. Even small defects can increase emissions by orders of magnitude. This leads to a situation where a few engines with very high emissions dominate fleet emissions (Fig. 1).


Fig. 1: Cumulative contribution to particulate emissions. 90% of the emissions come from about 10% of the vehicles (Burtscher et al., 2019)

This is true for road vehicles as well as for off-road applications (construction machinery, etc.). This is why periodic emission monitoring needs to be reintroduced. For construction machinery and other off-road engines, this is already the case in Switzerland.


In order to carry out the monitoring in practice, suitable measuring instruments with following features are required:

  • Allows easy measurement of particle number concentrations
  • Since the entire sensor is heated, emission measurements can be made without dilution
  • Concentration range up to 5,000,000 particles/cm3.
  • Long maintenance interval as no liquid, no dryer is used and only a few particles are deposited in the instrument
  • Can be used standalone or communicate with PC/tablet via Bluetooth, where the report is also generated for official measurements.
  • Is METAS certified according to regulation SR 941.242 (certificate CH-K4-20002-00)


In a project funded by the Swiss Federal Office for the Environment (BAFU) researches of the FHNW have developed a Handheld Emission Particle Counter (HEPaC). It is based on the Partector 2 of the company naneos, a spin-off of the FHNW.

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Fig. 2: Configuration of the HEPaC: The exhaust gas is heated to 195°C before it enters the sensor. The particles are then charged by a unipolar diffusion charger, followed by a pulsed separator and the measurement stage where the induced current is measured. More on the function in Fierz, 2014.

The HEPaC can be purchased at naneos, an FHNW spinoff.

The HEPaC can be used for following applications:

  • Emission measurements of combustion engines
  • Official periodic control measurements according to Swiss ordinance SR 941.242 for construction machinery and other off-road engines
  • Fleet emission tests


Figure 3: Efficiency as a function of particle size, the orange dots show the minimum efficiency prescribed in the regulation, the gray ones the maximum.


Project Information

Client and funding
Swiss Federal Office for the Environment (BAFU),
BAFU Umwelttechnologieförderung, Vertrag UTF 601.1319
ExecutionFHNW Institute for Sensors and Electronics, naneos
Duration2 Years
Project lead
Prof. Dr. Heinz Burtscher