Charge-Based Measurement of Ultrafine Particles: From Mobility Spectrometers to Widely-Deployable Monitors

Speaker BIO:

"Robert Nishida is an Assistant Professor in the Department of Mechanical and Mechatronics Engineering at the University of Waterloo. His research group develops new methods to measure aerosols and understand their impacts, with a focus on particle charging, transport phenomena, and low-cost sensors for fine and ultrafine particles. The group combines experiments and in-house modelling to identify and quantify the physical processes governing aerosol behaviour, translate these into new measurement methods and instrumentation, and apply them to real-world air quality problems, including emerging regulatory needs. He is also the CEO and Co-Founder of Atmose Ltd., which develops commercial aerosol measurement technologies.

Dr. Nishida completed his PhD at the University of Cambridge, where he received a Doctoral Thesis Prize from the UK Aerosol Society for his thesis on charge-based measurement of ultrafine particles. He is an Associate Editor of the Journal of Aerosol Science."

Invited talk abstract:

Exposure to fine particulate matter is the leading environmental risk to human health. Increasing evidence suggests that ultrafine particles (UFPs, <100 nm) are associated with distinct health effects due to their high number concentrations, surface areas, and deposition efficiencies in the lungs. Recognizing this evidence, recent guidance from the World Health Organization [1] recommends measurements of UFP number concentration and size distributions, and a subsequent 2024 European Union directive [2] requires these measurements across Europe toward full compliance by 2030. Together, these developments mark a turning point toward routine monitoring of UFPs.

Charge-based instrumentation has a deep history in aerosol science and underpins standard measurements of particle size distributions. Electrical mobility spectrometers (EMSs) determine size distributions by charging particles, classifying them by electrical mobility, and counting them, but their cost, size, and regulatory constraints have largely limited deployment to central monitoring sites. In parallel, a complementary class of charge-based monitors relies on diffusion charging, transport or trapping, and direct electrical detection to measure health-relevant metrics such as particle number or lung-deposited surface area (LDSA). Such approaches are already used at scale, with unipolar diffusion-charging instruments deployed across Europe for periodic technical inspections of diesel vehicles based on particle number concentration.

This talk describes how these charge-based approaches are connected through the common physical processes of ion–particle charging, transport, and electrometer-based detection. It emphasizes how these processes govern measurement accuracy, traceability, temporal response, and suitability for different applications. Recent developments in charge-based monitors are highlighted, including innovations that improve stability, reduce sensitivity to particle charge history, and enable operation with low-activity ion sources.

While reference instruments remain essential for scientific and regulatory measurements, advances in affordable charge-based monitors create new opportunities for widespread, real-time UFP measurement across indoor, outdoor, and occupational environments. Hyperlocal monitoring will improve health studies, support emissions regulation, and ultimately empower individuals to make evidence-based decisions about air quality.

References

[1] WHO global air quality guidelines. Particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva: World Health Organization (2021). ISBN 978-92-4-003422-8
[2] Council of the European Union. Directive (EU) 2024/2881 of the European Parliament and of the Council of 23 October 2024 on ambient air quality and cleaner air for Europe (recast). Official Journal of the European Union (2024). https://eur-lex.europa.eu/eli/dir/2024/2881/oj/eng