Quantification of Environmental Reactive Oxygen Species (ROS) by Chromo-Stoichiometry: Development and Validation of the Monagas Variant
Abstract
This research develops a quantitative model for estimating reactive oxygen species (ROS) in ambient air using a chromo-stoichiometric approach applied to the traditional Schönbein scale. Starting from the stoichiometric relationship between ozone (O₃) and water vapor as precursors of hydroxyl radicals (OH·), and considering ozone as the limiting reagent, a direct conversion is established between the Schönbein number and the OH· emission rate expressed in mol·cm⁻³·s⁻¹. This transformation results in the so-called "Monagas Variant," which converts a qualitative tool based on the colorimetric change of potassium iodide reagent strips into a quantitative method for radical estimation.
The model integrates the conversion of ozone concentrations (ppb) to amount of substance, the calculation of absolute humidity, and the application of stoichiometric relationships to determine the theoretical production of OH· during a standard 8-hour exposure period. The results allow for the classification of ambient oxidation into three levels (LOW, MIDDLE, and HIGH), defined by ranges of radical emission. Experimental validation, performed in a 1 m³ tank with an Open Air Factor (OAF) generator and through comparative tests with 17.5% hydrogen peroxide, showed consistent agreement between the observed color change and the values calculated by the model.
The data obtained, on the order of 10⁶–10⁷ mol·cm⁻³·s⁻¹, are consistent with values reported in the literature on ozone photolysis at air-water interfaces and atmospheric OH· production. Furthermore, it is shown that reliable determinations can be made in just 90 minutes, significantly reducing the evaluation time compared to the full 8-hour cycle. The Monagas Variant thus constitutes an accessible, reproducible, and low-cost tool for monitoring environmental oxidative capacity and assessing OAF in indoor spaces, offering a practical solution for the rapid control of advanced oxidation processes and indoor air quality.
Keywords
Hydroxyl radicals (OH·)
Reactive oxygen species (ROS)
Monagas Variant
Schönbein scale
Open Air Factor (OAF)
Chromo-stoichiometry
Indoor Air Quality (IAQ)
Advanced Oxidation Processes (AOPs)
Atmospheric environmental chemistry.
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Introduction
The recent COVID-19 pandemic has highlighted and accelerated, in just over three years, a large number of new trends, behaviors, regulations, and requirements surrounding indoor disinfection. The need to meet these disinfection requirements in public places, such as supermarkets, businesses, hospitals, and hotels, to maintain a pathogen-free environment as much as possible, has led to the reappearance and uncontrolled use of a multitude of existing products and substances, as well as new ones, mostly oxidizers. Some of these are already part of our daily lives, such as bleach, alcohols, peroxides, chlorinated compounds, ozone, etc.
Therefore, it is increasingly necessary to be able to quantify the role of oxidants in indoor environments, both for the air and for the surfaces where they are applied, since they all have a direct and indirect relationship with health: direct through dispersion in the environment through breathing and contact with these substances, and indirect through evaporation or methods of application that can end up in food and all kinds of consumer products.
Conclusion
Conclusions and Future Prospects
In conclusion, this research has successfully developed a robust chromo-stoichiometric model that transforms the traditional Schönbein Scale into a quantitative analytical tool. Thanks to the Monagas Variant, it is now possible to estimate OH· emission (expressed in molec·cm⁻³·s⁻¹) by simply observing a color change, allowing for efficient classification into three intensity levels (LOW, MIDDLE, and HIGH) with a response time of only 90 minutes. This advancement translates the complexity of stoichiometry to a visual scale, offering an accessible protocol for maintenance and monitoring teams without the need for expensive laboratory equipment.
The results obtained demonstrate consistency with the scientific literature on atmospheric radical production, positioning this system as an extraordinary bridge between qualitative observation and quantitative estimation. Its accessibility, reproducibility, and low cost make it an ideal solution for monitoring ambient oxidation and assessing the Open Air Factor in indoor spaces, where accuracy and speed are crucial.
Finally, this work lays the groundwork for future research. The scientific community is encouraged to continue refining the methodology using more precise photometric and colorimetric sensors. This technical evolution would allow a shift from visual to digital interpretation, paving the way for the development of portable tools and mobile applications. Integrating this methodology into everyday devices would bring radical monitoring to an unprecedented level of ubiquity and accuracy in the field of environmental health.
References
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