Online Monitoring of Particle-Bound Reactive Oxygen Species (ROS) and Oxidative Potential (OP) in a Changing Atmosphere: a Review

This review focuses on online monitoring technologies for particle-bound reactive oxygen species (ROS) in the atmosphere, highlighting recent advancements and remaining challenges. Reactive oxygen species (ROS) are chemically reactive molecules containing oxygen, including hydroxyl radicals (·OH), hydrogen peroxide (H2O2), and superoxide anions (O2·–). When these ROS are associated with particulate matter prior to inhalation, they are termed exogenous ROS or particle-bound ROS. These species are critical in atmospheric chemistry, influencing air quality, climate change, and public health through oxidative stress mechanisms. Traditional offline methods for measuring ROS suffer from limitations such as poor temporal resolution and degradation of short-lived ROS species during sampling and storage. Recent advancements in online monitoring technologies have addressed these limitations, offering higher sensitivity and improved temporal resolution. Online monitoring systems, such as automated instruments and continuous field deployment devices, now enable more accurate detection of ROS concentrations, contributing to better assessments of air pollution. In addition, this review discusses the oxidative potential (OP), defined as the capability of particles to trigger the production of endogenous ROS within biological systems following inhalation. Endogenous ROS are reactive oxygen species generated in vivo as a result of direct chemical reactions with particle components or biological responses, such as inflammation. By clearly distinguishing particle-bound ROS measurement techniques from those assessing OP, this review aims to clarify their complementary roles in evaluating air pollution and health implications. This review examines the limitations of traditional ROS measurement methods, discusses innovations improving measurement accuracy, and explores the role of ROS in atmospheric processes. It outlines future directions and emphasizes the importance of clearly distinguishing particle-bound ROS from OP in research, enabling effective air quality management and risk mitigation strategies.