Overview of Soot Emission Measurements Instrumentation: From Smoke and Filter Mass to Particle Number

Particulate emissions cause adverse health effects and for this reason they are regulated since the 80s. Vehicle regulations cover particulate emission measurements of a model before its sale, known as type approval or homologation. For heavy-duty engines the emissions are measured on an engine dynamometer with steady state points and transient cycles. For light-duty vehicles (i.e. the full power train) the particulate emissions are assessed on a chassis dynamometer. The measurement of particulate emissions is conducted either by diluting the whole exhaust in a dilution tunnel with constant volume sampling or by extracting a small proportional part of the exhaust gas and diluting it. Particulate emissions are measured by passing part of the diluted exhaust aerosol through a filter paper. The increase of the weight of the filter is used to calculate the particulate matter mass (PM) emissions. Vehicles are also checked during the course of their lives, i.e. those pulled over by authorities for roadside checks or the mandatory periodic inspection in a garage. In this case smoke is assessed with free acceleration tests. However, all these tests do not give any relevant information about the emissions of the vehicles during real driving conditions. This was only recently regulated. The particulate emissions on the road are measured with portable emission measurement systems (PEMS). The particulate emissions of newer vehicles decreased by more than two orders of magnitude since the 80s. The particulate measurement methods reached their detection limit and for this reason the particle number (PN) concentration was introduced in the European Union legislation as a new metric. In this paper a short summary of the particulate emission legislation of vehicles over the years is given. Then the instrumentation that has been used and is currently being used, like gravimetric filter measurement, is explained. In addition, other popular methods and instruments are analyzed, like chemical analysis of filters, light extinction, scattering and absorption instruments, electrical mobility and particle counting instruments. Correlation of the different instruments is discussed for different vehicle emission levels. Predictions for future instruments for low emission vehicles are given.