Different particulate mass (PM) portable emission measurement systems (PEMS) were evaluated in the lab with three heavy-duty diesel engines which cover a wide range of particle emission levels. For the two engines without Diesel Particulate Filters (DPF) the proportional partial flow dilution systems SPC-472, OBS-TRPM, and micro-PSS measured 15% lower PM than the full dilution tunnel (CVS). The micro soot sensor (MSS), which measures soot in real time, measured 35% lower. For the DPF-equipped engine, where the emissions were in the order of 2 mg/kWh, the systems had differences from the CVS higher than 50%.For on-board testing a real-time sensor is necessary to convert the gravimetric (filter)-based PM to second-by-second mass emissions. The detection limit of the sensor, the particle property it measures (e.g., number, surface area or mass, volatiles or non-volatiles) and its calibration affect the estimated real-time mass emissions. Thus, the choice of the real-time sensor might be critical if the emissions are close to the certification (or in-use) limit. Currently the emissions from DPF-equipped engines are almost an order of magnitude below the laboratory PM certification limit.The particle number (PN) method (measurement of non-volatile particles ≻23 nm with a condensation particle counter) had lower detection limit than the emissions of the DPF engine and the differences between the CVS and the partial flow dilution system SPC were within ±15% for all engines. One advantage compared to other real-time systems like DMM and MSS is that the number method is directly comparable to the certification results since PN limits will be introduced in the Euro VI heavy-duty regulation.