Preliminary Evidence of Exogenous Hydrogen Peroxide Formation via Plant Transpiration: Toward a Nature-Based Solution...

Plants play critical roles as nature-based solutions to maintaining air quality and regulating biogeochemical cycles, yet the mechanisms underlying these complex systems remain poorly understood. Hydrogen peroxide (H₂O₂), a globally present atmospheric oxidant, shows well-documented diurnal variation, but no direct link to plant transpiration has previously been reported. This study aimed to determine whether plants can produce exogenous H₂O₂ through transpiration and condensation, thereby revealing a novel pathway by which plants influence proximal and potentially global atmospheric chemistry. To investigate this, we examined a natural plant system undergoing photosynthesis and transpiration; our work was inspired by recent laboratory findings where spontaneous H₂O₂ was generated during the condensation of water vapour into microdroplets in engineered systems. Condensed water collected near leaf surfaces revealed H₂O₂ concentrations of 1-5 ppm, verified using both commercial peroxide test strips and spectrophotometric titration. Importantly, H₂O₂ production occurred only under light conditions when plants were transpiring, while controls without plants or without light showed no detectable levels. A strong distance-dependence was also observed, with minimal to no H₂O₂ detected beyond 40 cm from leaves. These findings suggest that plant-driven formation of water vapour and subsequent condensation produces measurable H₂O₂, establishing a previously unrecognized mechanism with implications for air quality improvement, atmospheric oxidation processes, and climate change modelling and mitigation.