Using Atomized NaI Particles as a Counting Efficiency Booster for Partial Calibration of Periodic Technical Inspection Reference Particle Counters

Helmut Krasa, Martin Kupper, Mario Anton Schriefl, ALEXANDER BERGMANN, Graz University of Technology

     Abstract Number: 303
     Working Group: Instrumentation and Methods

Abstract
In the second half of 2023, Germany will introduce PN emission measurements as part of the Periodic Technical Inspection (PTI) for passenger cars, which will require every EURO 6 homologized car to have its particle number (PN) emissions assessed with the PTI [1]. Thus, a large number of PN counters will be in use and a fast and simple calibration method is required. Condensation particle counters (CPCs) fulfill the PTI counting efficiency (CE) limits and are well-established devices for homologation measurements. Therefore, these devices often may be used as reference instruments for in-field PTI PN counters. In this work, we present an in-field calibration of the linearity and plateau CE for PTI reference counters using atomized NaI.

Particle generation with an atomizer allows for compact and energy-efficient generation of nanometer-sized salt particles. We use atomized NaI and show that is detected down to 18 nm with >90% CE for homologation CPCs, which have their adjusted cut-off size at 23 nm [2]. The CE is also evaluated for different salts for comparison.

The mean diameter of the NaI particle size distribution correlates with the salt concentration in the solution. At 1.2 w% NaI, a mean diameter of 46.8 nm and standard deviation of 1.7 was obtained [2]. Due to the higher CE of NaI compared to other particles, the reduction in CE of polydisperse particles compared to monodisperse particles in the plateau region was less than 1%. Measurements for particle concentrations between 80 and 30 000 cm² showed excellent linearity, with an R² > 0.99.

With NaI the plateau CE and the linearity can be calibrated without the use of a differential mobility analyzer, using only a portable atomizer, compressed air and a reference counter, enabling partial in-field calibration.

[1] BMDV (2021). Anlage VIIIa Straßenverkehrs-Zulassungs-Ordnung (StVZO). VkBl. Nr. 8, 404.
[2] Krasa H, Kupper M, Schriefl M. A & Bergmann A (2023), Aerosol Sci. and Techn. 57:4, 329-341.