Nanoparticles: how small can you go?

Nanoparticles: how small can you go?
15 February 2017

Improving urban air quality is the major impetus for a continuing push towards monitoring and regulating particle emissions. Now attention is extending to include particles significantly below the threshold of current regulation, approaching the molecular range – and Ricardo is spearheading some of the latest research in this area as well as helping industry comply with existing and future regulation.

In the continuing endeavour to control harmful emissions from motor vehicles, the measurement of particle numbers (PN) is now firmly a part of the European regulatory framework. The introduction of PN standards followed the pioneering work carried out by Ricardo and its partners in the early 2000s under the then UN-ECE GRPE (United Nations Economic Commission for Europe Groupe des Rapporteurs pour la Pollution et l’Energie) Particle Measurement Programme (PMP), an organization later brought under the auspices of the European Commission.

This ground-breaking initiative moved the application of particle emission control science on: as well as measuring the mass of particles, the approach was expanded to include the monitoring of individual particles.

Regulations now prescribe that in addition to meeting the previous massbased requirement, new vehicles must also emit fewer than 6x1011 particles per kilometre over the standard homologation drive cycle (currently NEDC, but to be replaced with the WLTC later in the year). This particle number limit is based on PN measurement above a (non-volatile) particle size threshold of approximately 23 nm. This limit was established both in terms of what was practical to achieve accurately and in a repeatable manner at the time, as well as representing the approximate primary particle size of soot or black carbon emitted as a result of incomplete combustion.

While PN measurement technology for automotive applications remains comparatively new, the particle number limit is also included in the Real Driving Emissions (RDE) element of the WLTP, meaning that the first generation of vehicle-based measurement systems must be PN capable.

While this is leading to a significant effort at supporting the roll-out of PN-based RDE, the very latest studies by Ricardo and its research partners are pushing even further, aiming to resolve particles of a size only marginally greater than the molecular level.

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