Prodigious Amounts of Hydrogen Oxides Generated by Corona Discharges on Tree Leaves

Abstract

Prodigious amounts of the hydroxyl radical (OH) are generated in the laboratory on tree leaves by corona discharges, which also occur on trees during thunderstorms. Production rates of OH and HO₂ depend on the applied electric field generating the corona discharge, leaf dryness, and the presence of liquid water on the leaf. However, they are independent of leaf type and corona discharge polarity for a given corona ultraviolet (UV) flux. Production rates of OH, HO₂, and O₃ strongly correlate with corona UV flux. Although the contribution of corona-produced OH to total global OH production is unlikely to be important, corona-generated OH is likely a few orders of magnitude greater than oxidation by known processes in the vicinity of the affected leaves, potentially influencing atmospheric oxidation and tree and forest ecology.

Key Points

• Extreme hydroxyl and hydroperoxyl radicals are generated by corona discharges on leaves from several different tree species

• The measured hydroxyl and hydroperoxyl radicals show a strong linear correlation with ultraviolet flux from the corona

• Atmospheric oxidation likely increases by orders of magnitude near corona on tree leaves during thunderstorms

Plain Language Summary

When thunderstorms pass overhead, electrical discharges called corona can be induced on trees. We found that corona discharges on several different species of tree leaves in the laboratory generated extreme amounts of the atmosphere's primary oxidant, the hydroxyl radical (OH), and the closely related hydroperoxyl radical (HO₂). The production rates of OH and HO₂ from corona discharges depend on several factors, but correlate most strongly with the ultraviolet flux generated by corona discharges. While little is known about corona discharges on trees, such as how many trees and how many leaves develop corona discharges during thunderstorms, we estimate that corona generated on trees under thunderstorms could have substantial effects on the air at the tops of trees and perhaps the tree leaves themselves. Billions of trees living on Earth's surface are being impacted daily by thunderstorms, indicating that a deeper investigation into this new OH and HO₂ source is required.