Research progress on online monitoring systems for oxidative potential of atmospheric particulate matter

In recent years, with the continuous advancement of atmospheric pollution control efforts, the health effects arising from the complex sources and diverse physicochemical properties of particulate matter have garnered increasing attention from scholars. The oxidative potential (OP) of atmospheric particulate matter has gradually emerged as a key indicator for assessing air quality and health risks in the field of environmental health, becoming one of the major research focuses in recent years. OP effectively reflects the capacity of particulate matter to induce the generation of reactive oxygen species and trigger oxidative stress responses, which is closely linked to a range of adverse health outcomes, including cardiovascular and respiratory diseases. Therefore, accurate measurement of the OP of particulate matter is of paramount importance for the in-depth evaluation of its health impacts, the refinement of air quality standards, and the formulation of precise public health intervention strategies. Traditionally, the measurement of OP has relied primarily on offline filter sampling and laboratory analysis techniques. Such methods are often limited by low temporal resolution, notable analytical delays, high economic costs, and the potential loss of short-lived, highly reactive oxidative components during the detection processes. These limitations present challenges for studies based on offline measurements to capture the rapid dynamic changes in atmospheric OP or to enable real-time warning and source apportionment during pollution events. To overcome the bottlenecks associated with conventional offline measurement techniques, researchers have dedicated considerable efforts in recent years to developing rapid and automated detection techniques based on various principles, aiming to achieve real-time online assessment of the OP of atmospheric aerosols. The advancement of such techniques: (1) reveals the diurnal variation patterns of atmospheric OP and its dynamic linkages with pollutant source emissions, meteorological conditions, and chemical processes, and (2) provides novel technical approaches for evaluating real-time air quality from a biologically relevant perspective and for assessing population exposure risks.This review systematically summarizes research progress in the field of online detection of atmospheric aerosol OP over the past 25 years. It elaborates on the technical principles of automated online monitoring systems and provides a comprehensive overview of the development history and current status of various detection devices and methods. Specifically, the study categorizes, introduces, and compares six major types of online monitoring systems, including: (1) systems based on the 2ʹ,7ʹ-dichlorofluorescin (DCFH) assay; (2) particle into Nitroxide Quencher (PINQ) technology, (3) the ascorbic acid redox system (AA-only), (4) automated dithiothreitol (DTT) assay platforms, (5) online hydroxyl radical monitoring systems, and (6) online monitoring systems coupling OP measurement with cytotoxicity assessment. These approaches are further compared from multiple perspectives, such as detection sensitivity, measurement specificity, temporal resolution, operational complexity, economic cost, and physiological relevance. Finally, the review thoroughly analyzes the advantages and challenges faced by these automated technologies in practical monitoring scenarios. Looking ahead, future research directions in online OP monitoring technology should focus on promoting the standardization and mutual recognition of measurement methods, developing probe systems with higher sensitivity and greater specificity, achieving multi-parameter synchronous online monitoring and comprehensive data integration, as well as expanding their applications in areas such as individual exposure assessment and rapid evaluation of the effectiveness of air pollution control measures. This paper aims to provide systematic scientific references for methodological innovation, technological advancement, and the formulation of health effect-based environmental policies.