Monitoring Reactive Oxygen Species (ROS) in High-Altitude Cities of Bolivia: Theoretical Foundations and Evaluation of an Active ABTS-Based Sampling Methodology

Air pollution monitoring in Bolivian high-altitude cities—La Paz (3,600 m a.s.l.), El Alto (4,100 m), Oruro (3,706 m), Potosí (3,976 m), and Cochabamba (2,558 m)—relies exclusively on conventional criteria pollutants (PM₂.₅, PM₁₀, NOₓ, SO₂, CO, and O₃), which fail to fully capture the oxidative toxicity to which urban populations are exposed. Reactive Oxygen Species (ROS) constitute a chemically diverse group of highly reactive oxygen-derived compounds whose atmospheric formation is intensified by the particular physicochemical conditions of the Andean atmosphere: elevated ultraviolet irradiance, an aging high-emission vehicle fleet, redox-active transition metals in resuspended mineral dust, and frequent thermal inversion episodes. This paper presents the theoretical framework justifying the urgent need to incorporate ROS monitoring into Bolivia's air quality surveillance systems, and evaluates the methodological proposal of the MonROS project, which employs an active sampling system with an ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) capturing solution at pH 7.4 for the measurement of total atmospheric oxidant capacity. The proposed methodology is assessed in terms of its scientific soundness, analytical advantages, and current limitations, and its potential to generate the first baseline dataset of atmospheric oxidative potential (OP) for high-altitude Andean cities is discussed.