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Metrology for Portable Emission Measurement Systems (PEMS): Challenges and pathways of traceable calibration for particle number (PN)
by Dr. Andreas Nowak, Dr. Jorge Saturno, Prof. Volker Ebert


Particulate number emissions from vehicles are in the focus of the current EU legislation, because many of the European metropolitan areas struggle to fulfil air quality standards for particulate matter (PM). These emissions have a high variability in particle number (PN) concertation and are chemically dominated by black carbon (BC), also known as soot particles. Due to their morphology, they efficiently uptake organic vapors which further increases their toxicity. In 2012 the World Health Organisation (WHO) classified especially diesel engine exhaust as carcinogenic to humans. In order to ensure that ultrafine particulate emissions (PM 0.1 µm and below) can be monitored, the European Commission has introduced a two-step approach as type-approval process like test bench measurements as well as measurements during real driving emission (RDE) in order to fulfill limit values for particle number (PN) concentration. Beside this, particle number is a metric with existing and well-established calibration and measurement capabilities (CMC), available in different national metrology institutes (NMIs) in Europe. Several challenges arise when implementing aerosol particle count measurement in vehicle exhaust during RDE measurements. Those challenges comprise (i) harmonization of calibration procedures for different type of sensors, including condensation particle counters (CPCs) and diffusion chargers (DCs), (ii) quantification of ultrafine particles (UFP), i.e., below 23 nm in diameter, lack of reference nanoparticles, (iii) multiple charge correction for larger particles up to 200 nm (relevant above 70 nm), (iv) uncertainty budget under tailpipe conditions, and (v) lack of mobile PN transfer standards. Designing and implementing a traceable pathway for PN quantification of PEMS devices is one of the key goals of the EMPIR project “MetroPEMS” lead by PTB. Moreover, the aim of the project is to validate and determine the performance of the current state-of-the-art PEMS devices by comparison with traceable PN calibration facilities and finally a “concept of golden PEMS” to establish as a transfer standard. Therefore, the project investigates commercially available PN-PEMS devices including dilution systems upstream of the particle counters as well as volatile particle remover (VPR) systems which are used to remove volatile compounds from exhaust emissions. The improvement of PN calibration capabilities will benefit emission control policies and will help to improve emission inventories. Moreover, the research outputs from the MetroPEMS project will improve PN determination with spin-off effects in the field of aerosol research


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Topic : Theme 1: Atmospheric Chemistry and Physics.
Reference : T1-A32

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