Fascinating new research from atmospheric scientists at Penn State University has found during thunderstorms, electrical discharges on tree leaves can generate significant volumes of chemicals that may affect the air quality in surrounding forests.
Back in 2021 meteorologist William Brune and colleagues published a key study in the journal Science demonstrating how lightning leads to the formation of several atmospheric oxidants, including hydroxyl radical (OH) and hydroperoxyl radical (HO2). These gaseous molecules are crucial "cleansing" agents in our atmosphere. They can degrade greenhouse gases such as methane, however, hydroxy radicals can also be unhelpful, producing high levels of ozone when encountering oxygen.
The study estimated thunderstorms may account for up to 16% of all global atmospheric OH. Follow-up work has led the researchers to investigate other ways thunderstorms could trigger the formation of hydroxy radicals.
“The hydroxyl radical contributes to the total atmospheric oxidation of many atmospheric pollutants, including the greenhouse gas methane, improving air quality, and slowing climate change," explained Brune. "However, these reactions can also lead to the formation of ozone and small aerosol particles, negatively affecting air quality and climate. So understanding all the potential sources of OH is important for predicting future air quality and climate.”
The researchers looked at a phenomenon where thunderstorms can induce small electrical discharges on objects on the ground. These discharges are known as coronas and can be particularly prominent on plant leaves with sharp points.
So the question the researchers wanted to answer was whether plant coronas generate measurable levels of OH chemicals.
In lab conditions the researchers tested eight different kinds of tree leaves, and the results revealed these plant coronas did indeed generate extreme amounts of OH. While the overall volumes of OH generated by plant coronas are significantly lower than what is found within thunderstorms, the researchers do speculate the size of large forests could lead to the extreme OH levels around the time of thunderstorms.
“Even though the charge generated by the corona was weaker than the sparks and lightning we looked at before, we still saw extreme amounts of this hydroxy radical being made,” said Jana Jenkins, another researcher working on the project. “There are about two trillion trees in areas where thunderstorms are most likely to occur globally and there are 1,800 thunderstorms going on at any given time. This is definitely a process that’s going on all the time and based on the calculations we’ve been able to do so far, we think this can affect air quality in and around forests and trees.”
While the researchers are clear this newly discovered mechanism is unlikely to be relevant in terms of global OH production, what could be relevant is the way these waves of atmospheric oxidation can influence tree and forest ecology. Jenkins also suggests with climate change increasing the amount of thunderstorm activity it is crucial to understand these processes, particularly in terms of the effect on local air quality in these locations.
The new study was published in the Journal of Geophysical Research: Atmospheres.
Source: Penn State University
