During transients, engines tend to produce substantially higher peak emissions which are the longer the more important as the steady state emissions are better controller. To this end, they must be measurable in an adequate time scale. While for most emissions there are commercially available sensors of sufficient speed and performance, the same is not true for soot, especially for production engines. Against this background, in the last years we have investigated together with a supplier of measurement systems the possible use of a 50Hz sensor based on LII and of the same size of a standard oxygen probe, and the results were very positive, showing that the sensor could recognize transient changes undetected by conventional measurement systems (like AVL Opacimenter or Microsoot) but confirmed e.g. by incylinder 2 color spectroscopy. The higher speed is also due to the position, as the sensor can be mounted above or below the turbine in a turbocharged CI engine. In this paper, the main concern is accuracy which can be improved by combining the output of the photodiodes of the sensor with operation information of the engine, e.g. the pressure and temperature near to the sensor location. In this way, the steady state accuracy could be proven and the plausibility of the dynamic accuracy shown by filtering/deconvolution methods. Interestingly, the sensor reproduces a combustion variability consistent with the two color spectroscopy in the cylinder and allows also to distinguish the contributions of the different cylinders. The paper shows also the improvement of the measurement produced by the combined use of sensor and engine information. All measurements concern raw emissions of a production 2 lt Euro 5 CI engine.