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JRC publishes assessment report on PEMS measurement uncertainty

27 February 2020

The EU Joint Research Center (JRC) has released an assessment report of portable emissions measurement systems (PEMS) measurement uncertainty, suggesting that the RDE conformity factor (CF) for NOx be lowered to 1.32, down from the current 1.43. Since JRC is the official scientific body of the European Commission, such a change is likely to be implemented by a future RDE “package” or at the Euro 7 stage.

The report describes an experimental campaign carried out by the JRC during 2018 and 2019 to assess zero drift of PEMS gas analyzers under real life operation. The instruments considered in the analysis, from four manufacturers, cover probably the whole PEMS market in Europe. The tested instruments belong to the generation of PEMS currently available in the market.

The results of the testing campaign—measuring zero every 10-20 min on the road—showed that there is not a systematic positive or negative drift, neither a systematic step nor linear drift for any of the pollutants considered (NO, NO2, CO2, CO) for all PEMS instruments tested. On most of the tests performed, the zero drift for NOx was lower than 3 ppm under a variety of ambient temperature and humidity conditions. Additional tests under more stringent environmental conditions (high altitude mountain driving) showed a similar pattern for zero drifts of all pollutants.

The report concludes that the evidence gathered during the campaign did not verify the worst case drift scenario used to define the 0.43 NOx margin, and it can be used to justify a further reduction of the margin value. Based on the worst case scenario for zero drift of the JRC testing campaign and considering the effect on a vehicle with large engine displacement (largest effect in terms of NOx mass), the updated NOx margin that is proposed is 0.32.

The PEMS units tested in the study were: AVL MOVE, Horiba OBS-ONE, MAHA-AIP PEMS (Gen2) and Sensors SEMTECH LDV. The systems were tested on a range of light-duty vehicles powered by gasoline, diesel, as well as CNG and LPG engines.

Source: Technical Report JRC114416