2022-10-18 ペンシルベニア州立大学(PennState)
Weak electrical discharges, called corona, can form on tree leaves during thunderstorms Credit: Penn State . All Rights Reserved.
研究チームは、コロナが、ヒドロキシルラジカル-OH-とヒドロペルオキシルラジカル-HO2-を極めて大量に発生させることを発見した。ヒドロキシルラジカルは、大気中で重要な化学反応を引き起こし、メタンのような温室効果ガスを除去する一方で、オゾンやエアロゾル粒子汚染を引き起こす。
コロナによって生成されたOHは、雷雨の際に樹木の周りで通常の100倍から1,000倍に増加する可能性があると、科学者たちはJournal of Geophysical Research誌に報告している。
OHは葉から自然に放出される炭化水素と反応してオゾンや粒子状物質を生成するため、OHレベルの上昇は大気環境に影響を与える可能性がある。
研究者たちは、8種類の樹木の葉を、雨を想定した濡れた状態などさまざまな条件下で実験室実験を行った。
その結果、コロナ放電によって生成されるOHとHO2は、樹種を問わず、放電によって発生する紫外線と強い相関関係があることがわかった。
＜関連情報＞
- https://www.psu.edu/news/research/story/electric-discharges-leaves-during-thunderstorms-may-impact-nearby-air-quality/
- https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022JD036761
コロナ放電による酸化水素の樹木葉への大量発生 Prodigious Amounts of Hydrogen Oxides Generated by Corona Discharges on Tree Leaves
J. M. Jenkins,G. A. Olson,P. J. McFarland,D. O. Miller,W. H. Brune
Journal of Geophysical Research: Atmospheres Published: 09 August 2022
DOI:https://doi.org/10.1029/2022JD036761
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.
