High-temperature solid particle emission measurements in the sub-23nm mobility size range with the Advanced Half-Mini DMA
Current particle number related vehicle emission legislation is limited down to 23 nm. The rationale behind the 23 nm cut-off size is based on the avoidance of significant uncertainties created during sampling and measuring sub-23 nm solid particles. Difficulties in introducing a robust measurement protocol in this particle size range led regulation authorities to ignore their contribution to ambient pollution. However, the sub-23 nm particles draw high attention since current gasoline engines emit almost equal fraction of sub- and above- 23 nm particles, while diesel engines with after-treatment devices may also emit such ultrafine particles under certain conditions (i.e. regeneration of particulate filters) (Giechaskiel and Martini, 2014). Number concentration measurement certification methods rely exclusively on a protocol defined from the Particle Measurement Programme (PMP) working group. Accordingly, the raw exhaust is driven to a full flow dilution tunnel and subsequently to a Volatile Particle Remover (VPR) to remove possible volatile and semi-volatile material that condenses on solid particles or creates a separate nucleation mode. The VPR consists of a hot and a cold dilution stage while an evaporation tube or a catalytic stripper (CS) are inserted between these two dilution stages. One of the problems identified with the standard sampling procedures is the potential formation of particles in the sub-23 nm region, the so-called artefacts, as well as the high particle losses due to diffusion. To overcome the above-mentioned uncertainties we investigate a novel approach for sub-23 nm measurements that necessitates a single hot dilution stage and a high-temperature size classification measurement with the Advanced Half-Mini Differential Mobility Analyzer (HM-DMA). The Advanced HM-DMA system is a supercritical DMA, with a 2 cm working section, able to classify aerosol particles in the mobility size range 4 – 30 nm with high resolution and fast spectrum acquisition (de la Mora, 2017). Due to recent ...
