Assessing the Oxidative Potential of Atmospheric Particulate Matter by Dithiothreitol (DTT) Assay: Mechanistic Insight, Instrument Development and Applications of Real-Time Monitoring

Abstract

Ambient particulate matter (PM) pollution, particularly fine particulate matter (PM2.5), poses a significant threat to public health, contributing to millions of premature deaths and a substantial burden of disease globally. The complex composition of PM_2.5, including transition metals and redox-active organics, catalyzes the formation of reactive oxygen species (ROS) in human lung fluid, leading to oxidative stress and various health impacts. Oxidative potential (OP), defined as the capacity of PM to consume antioxidants and generate ROS, has emerged as a crucial metric for assessing PM toxicity. This thesis presents comprehensive investigations into the OP of PM as assessed by the dithiothreitol (DTT) assay, with a focus on elucidating the underlying mechanisms, developing innovative monitoring techniques, and exploring the applications of real-time monitoring for effective air quality management.

This thesis consists of four major parts:

(1) Mechanistic Insights: This work explores the nonlinear concentration-response relationships associated with transition metals, particularly copper (Cu) and manganese (Mn), within the DTT assay framework. We elucidate a quasi-Michaelis–Menten mechanism that quantitatively describes the interactions between these metals and OP, contributing to a deeper understanding of how these chemicals influence OP.

(2) Innovative Monitoring Instrumentation: We develop a novel online monitoring instrument that employs a particle-into-liquid sampler (PILS) combined with advanced light absorption measurement techniques. This system facilitates continuous, real-time assessments of PM_2.5 OP, effectively addressing the limitations of traditional filter-based methods and capturing transient pollution events.

(3) Impact of Firework Emissions: This study investigates the acute impact of firework emissions on PM_2.5 OP during the Chinese New Year, revealing a dramatic surge in OP values. It highlights the nonlinear response characteristics associated with redox-active metals while examining the role of organic compounds in driving these changes.

(4) Long-Term Monitoring: This study examines the OP of PM_2.5 in Hong Kong through continuous hourly monitoring over 17 months, providing a comprehensive dataset to enhance understanding of PM_2.5 toxicity. Our findings reveal significant seasonal variations in OP and PM_2.5 levels, with specific pollution episodes used as case studies. This research highlights the importance of OP as a key metric for assessing PM_2.5 toxicity and emphasizes the need to integrate OP measurements into air quality assessments.

Overall, this thesis enhances the understanding of PM_2.5 OP and its health implications while advancing real-time monitoring techniques that can inform effective air quality management and public health strategies.

Date of Award	2026
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jianzhen YU (Supervisor)