Webinar title: Sulfate Formation via Photosensitized Oxidation by Incense Burning Particles
Speaker: Chak Chan
Webinar time: 15:00 pm, July 2, 2025 (Wednesday)
Venue: Room 200, New Environmental Building
Inviter: Yue Zhao, Chenxi Li
Abstract:
Incense burning, a common ritual in Asian cultures, especially in coastal cities, emits significant particles in temples and households. Particulate aromatic carbonyls, key components of incense burning aerosols, contain photosensitizers that can produce oxidants for in-particle oxidation such as sulfate formation from SO2. Using single particle aerosol mass spectrometry (SPAMS), we observed that sulfate formation in incense burning particles does not solely depend on traditional gas-phase reactions. Instead, it is significantly influenced by photosensitization, which is dependent on various environmental conditions such as relative humidity and UV light exposure. Furthermore, internally mixed incense burning and sea-salt particles are often found in coastal regions. We observed enhanced sulfate production in laboratory-generated droplets containing incense smoke (IS) extracts and sodium chloride (IS−NaCl) over pure NaCl droplets under irradiation, attributable to photosensitization induced by IS constituents. Photosensitizers like vanillin (VL) and syringaldehyde (SyrAld) found in IS samples can markedly accelerate SO2 oxidation. Moreover, the excited triplet state of the photosensitizer might interact with chloride ions to generate reactive chlorine species. Such synergistic effects between chlorine chemistry and photosensitization could further enhance sulfate formation. Additionally, the aging of IS particles further promoted sulfate production. This is likely due to increased secondary oxidant production driven by a higher proportion of nitrogen-containing species relative to fresh IS particles. Our studies highlight the substantial impact of photosensitized oxidation processes in sulfate production, particularly in areas impacted by incense burning, offering new insights into atmospheric sulfate formation mechanisms. The similarity between incense burning and biomass burning particle mass spectra suggests that biomass burning may also trigger sulfate formation. Using sulfate formation as a tool, we demonstrate that photosensitization of incense burning aerosol can enhance the atmospheric oxidative capacity and promote secondary aerosol formation.
About the speaker:
Prof. Chak Chan joined King Abdullah University of Science and Technology (KAUST) in May 2023 from the City University of Hong Kong (CityU), where he most recently served as Dean of the School of Energy and Environment (SEE). He obtained his bachelor’s and Ph.D. in Chemical Engineering from the University of Texas, Austin, and Caltech, respectively. After studying in the US, he joined the Chemical Engineering Department of the Hong Kong University of Science and Technology (HKUST), rising in ranks from Lecturer/Assistant Professor to Professor in Chemical Engineering and Associate Head. In 2009, he became the Founding Head of the Division of Environment (ENVR), a new interdisciplinary academic unit focusing on the science and technology of the environment and its impacts. Chak joined CityU in December 2015 as the second Dean of SEE and has more than 14 years of administrative experience as an Associate Head, Head, and Dean in interdisciplinary research and academic programs. Chak’s research focuses on the atmosphere's physical chemistry, particularly the chemistry of airborne particulate matter. His academic achievements include publishing over 250 SCI journal papers, over half as the corresponding author, and a SCOPUS citation, to date, of over 16,000 with an h-index of 61, and Google scholar citation of over 20,000 with an h-index of 66.