Abstract
Significant diesel engine technology improvements have been propelled by the reductions brought on the mass-based emission standards. Additionally, aftertreatment devices started also appearing, while fuel quality is much refined compared to the past, in an effort to control emissions from present and future vehicles. However, current research at international level intensively focuses on a more detailed particle emission characterisation, establishing a discrete shift in the perception of particle emissions, with mass representing only one dimension of the issue. In view of the new scientific targets, this paper first aims at identifying the needs that called for a broader particle emission characterisation. At a second step, alternative metrics are explored that may be used for emission quantification. Thirdly, we outline the fundamental criteria that need to be met in developing a particle measurement protocol. Finally, such a protocol is used to comparatively assess the effects of engine technology advance on a number of important particle properties.