Professor Ta-Chih Hsiao is a leading aerosol scientist at National Taiwan University and Joint Research Fellow at Academia Sinica. His research focuses on ultrafine particle dynamics, aerosol health effects, and advanced monitoring technologies.

Early in my career I recognized a persistent gap: while mass-based particulate matter (PM) metrics dominate regulations, ultrafine particles (UFPs), because of their high surface area, dynamic chemistry, volatility, and lung-depositing behavior, are poorly characterized and regulated. This recognition led me to develop and deploy novel instrumentation (for example, coupling H-TDMA–APM, ATM-DMA–spICP-MS) to measure size, effective density, hygroscopic growth, volatility, and lung-deposited surface area (LDSA) of UFPs. By doing so, I established a measurement foundation that yields richer exposure metrics than mass alone.
With advanced measurement capability in hand, I extended my work to probe source, transformation, and health-relevant metrics. I identified, for example, how traffic and industrial emissions contribute to UFP number concentration, effective density, and surface area; how atmospheric aging/hygroscopic growth influences optical properties and visibility; and how PM₁‐bound trace metals contribute to estimated lifetime cancer risk (ELCR) when assessed on a LDSA basis rather than a mass basis. These insights reinforce that UFPs cannot be understood solely through mass-based frameworks.