Large eddy simulation of the dispersion of short duration emissions: Implications for the metrological evaluation of remote sensing devices for on-road emissions monitoring.

Remote sensing techniques have emerged as valuable tools for characterizing pollutant emissions from large vehicle fleets and identifying high emitter single vehicles in real driving conditions. Nevertheless, the use of these systems for official emission control purposes by public administrations is an issue because the remote sensing devices must obtain official metrological certification, which currently lacks an international technical standard. The fluid dynamic study that we present demonstrates the promising potential of using pulsed synthetic reference plumes of known chemical composition in order to simulate exhaust emissions produced by combustion engine vehicles in a repetitive and controlled way. This scheme would facilitate the implementation of these complex metrological certification tests and drastically reduce the potential costs associated to these certifications and the emission of gases. In this paper, the atmospheric dispersion of the synthetic puff-like plumes after being released from a vehicle has been studied through fluid dynamic simulations, in order to identify their optimal usage conditions as reference materials. The simulations have allowed to study the evolution of two types of reference short plumes (puffs generated at 2 and 6 bars) from a vehicle at static and dynamic conditions. Results show that, in spite of the fast dispersion of these puffs, it is possible to accurately determine their chemical composition by optical techniques, for instance, by differential absorption spectroscopy. This opens the way for designing advanced and robust metrological evaluation procedures that could be the basis of a future technical standard for the certification of optical remote sensors of traffic emissions. This would allow future deployment of those certificated remote sensors on roads, contributing to a sustainable mobility and effective air pollution management strategies.