Spontaneous Hydroxyl Radical Production in Leaf Dew

Dew frequently forms on plant leaves, yet its chemical reactivity has long been overlooked. Here, we demonstrate that leaf dew can spontaneously generate hydroxyl radicals (•OH) during condensation, revealing dew as a previously unrecognized, redox-active interfacial reactor. Using controlled temperature-driven condensation–evaporation cycles combined with electron paramagnetic resonance and chemical probe quantification, we show that •OH is ubiquitously produced in dew at 5.7–23.9 nmol m–2 on diverse plant species and can be sustained over repeated dew-formation events. The yield of •OH is strongly regulated by leaf surface properties and environmental conditions, increasing with surface hydrophobicity, relative humidity, and lower temperatures. Enhanced hydrophobicity promotes the formation of spherical microdroplets with larger specific interfacial areas, confirming that •OH generation is primarily interface-driven. Moreover, we demonstrate that spontaneously generated •OH in dew can initiate the oxidative transformation of surface-deposited pollutants, exemplified by the hydroxylation of imidacloprid. These findings establish leaf dew as a transient but ubiquitous hotspot for oxidative chemistry, with potential implications for pollutant fate, vegetation-mediated self-purification, and biosphere–atmosphere interactions.