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Portable Emissions Measurement Systems (PEMS) represent a robust and accurate solution to study the in-use emissions of combustion engines. The application of PEMS is now ranging from large engines to the smallest light-duty vehicles. The current commercially available PEMS exhibit measurement performances that are close to the ones of laboratory grade systems; when PEMS data are analysed with an adequate method, the test results allow a detailed insight into the on-road emissions performance of the vehicles with respect to their behaviour on the standard laboratory test cycles. The development of representative test cycles, which has become a typical approach in the last years, supposed to address special driving situations, now becomes less efficient because of the effort needed for their development and the poor representativeness of the results. In this light, PEMS testing offers an easy and efficient way to evaluate the vehicle emissions over a huge variety of conditions.

Portable Emissions Measurement Systems (PEMS) are becoming an important regulatory tool to monitor the in-use compliance of large sources like heavy-duty vehicles (HDV) or non-road mobile machinery (NRMM). Legislative research programmes in Europe, United States and Japan are introducing PEMS in the regulations. The application of PEMS to light-duty vehicles (LDVs) is not part of or driven by official legislative requirements. However, as the vehicle-engine operation points in the laboratory test cycles are limited, emissions and fuel consumption under real world driving conditions can differ significantly from those measured under controlled laboratory conditions. The present paper discusses the application of PEMS to real-world emission measurements of passenger cars, under the light of the existing instruments and test protocols already developed for heavy-duty vehicles. Data are reported for a measurement campaign carried out in downtown Milan.