Oxidative Potential of Ambient PM and Related Health Endpoints over South Asia: A Review

South Asia occupies only about 3.5% of the world’s area but, about 25% of the average world’s population lives here and is continuously exposed to severe air pollution. Unprecedented development activities in most of the South Asian cities emit primary and secondary pollutants into the atmosphere. Particulate matter (PM), a principal air pollutant, are tiny enough to remain suspended in the atmosphere for a long time (about a week). They can penetrate the human nasal airway and damage the lungs. PM effects on human health are assessed based on their mass concentration, size distribution, and chemical composition. Despite being critically important, studies related to PM effects on human health are limited over South Asia. In recent years, only a few South Asian research groups started studying the ability of atmospheric PM to cause human health hazards by generating in situ reactive oxygen species (ROS). The capability of atmospheric PM to produce ROS and/or deplete antioxidants is termed as their oxidative potential (OP). Though limited, efforts are made to identify particular species with the higher OP. Atmospheric aging of PM can also alter their OP. No studies from South Asia, except a few from India, investigated how the atmospheric aging changes the chemical and physical properties of PM and affect their OP over South Asia. These studies also showed that OP depends more on PM composition rather than its concentrations. Therefore, mitigation strategies for reducing PM mass concentrations alone may not be sufficient, and linking PM OP with significant health effects may be a better way to regulate specific sources of PM rather than overall PM mass. This review reports the necessities and limitations for PM OP studies in South Asia and future directions.