Lightning increases the atmosphere’s ability to cleanse itself by producing nitric oxide (NO), leading to atmospheric chemistry that forms ozone (O3) and the atmosphere’s primary oxidant, the hydroxyl radical (OH). Our analysis of a 2012 airborne study of deep convection and chemistry demonstrates that lightning also directly generates the oxidants OH and the hydroperoxyl radical (HO2). Extreme amounts of OH and HO2 were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO2 is orders of magnitude more than any previous atmospheric observation. Lightning-generated OH in all storms happening at the same time globally can be responsible for a highly uncertain but substantial 2-16% of global atmospheric OH oxidation.

Reaction with the hydroxyl radical (OH) is often the first step in the removal of many atmospheric pollutants. The nitrogen oxides (NOx) generated by lightning can increase the amount of HOx (HOx = OH + HO2) present in the atmosphere, but direct HOx production from lightning has never been quantitatively investigated in the laboratory. In this laboratory study, prodigious amounts of HOx were generated by both visible and subvisible electrical discharges over ranges of pressure and water vapor mixing ratios relevant to the troposphere. Also measured were NO, total nitrogen oxides (NOx), ozone (O3), and OH exposure, which is the integral of the hydroxyl radical concentration over time since the discharge. HOx and OH exposure were approximately independent of pressure from 360 to 970 hPa and increased only slightly as water vapor increased from 1,000 to 8,000 parts per million volume (ppmv), while NOx was approximately independent of both pressure and water vapor over the same ranges. These laboratory measurements of excessive HOx and OH exposure are similar to measurements of electrically generated HOx discovered in electrified anvil clouds during a 2012 airborne study, thus demonstrating the relevance of these laboratory results to the atmosphere and the importance of understanding the electrically generated HOx contribution to atmospheric oxidation.

Lightning plays a major role in tropospheric oxidation chemistry (Murray et al., 2013). It can produce nitrogen oxides, hydrogen oxides, and ozone through electrical discharges in the atmosphere. Electric discharges in gases have three regions, the dark discharge, glow discharge, and arc discharge, with voltage building up during the first two regions before suddenly dropping during the last region because of neutralization (National Research Council, 1986). We refer these three regions respectively as the subvisible discharge, corona discharge, and flash discharge for atmospheric lightning in this work.

Typical amounts of the atmosphere's most important oxidant, the hydroxyl radical (OH), can increase 1,000-fold when atmospheric electrical discharges such as lightning occur (Brune et al., 2021). This lightning-generated OH contributes to the total atmospheric oxidation of many atmospheric pollutants, including the greenhouse gas methane, improving air quality, and slowing climate change. However, these OH reactions can also lead to the formation of ozone and small aerosol particles, negatively affecting air quality and climate. Therefore, understanding all the potential sources of OH is important for predicting future air quality and climate.Only recently have electrical discharges in thunderstorm anvils been shown to be a potentially significant source of global OH, accounting for as much as 2%-16% of global atmospheric OH oxidation (Brune et al., 2021). Laboratory measurements confirmed that OH and the closely related hydroperoxyl radical (HO 2 ) are generated in extreme amounts by both spark discharges and pulsed weak invisible discharges called subvisible discharges (Jenkins et al., 2021). Corona discharges, or simply corona, were not investigated in these previous studies, but they also generate chemical species including the hydrogen oxides (HO x = OH + HO 2 ), ozone (O 3 ), and the nitrogen oxides (NO x ) (

Atmospheric electrical discharges are now known to generate unexpectedly large amounts of the atmosphere’s primary oxidant, hydroxyl (OH), in thunderstorm anvils, where electrical discharges are caused by atmospheric charge separation. The question is “Do other electrical discharges also generate large amounts of oxidants?” In this paper, we demonstrate that corona formed on grounded metal objects under thunderstorms produce extreme amounts of OH, hydroperoxyl (HO 2 ), and ozone (O 3 ). Hundreds of parts per trillion to parts per billion of OH and HO 2 were measured during seven thunderstorms that passed over the rooftop site during an air quality study in Houston, TX in summer 2006. A combination of analysis of these field results and laboratory experiments shows that these extreme oxidant amounts were generated by corona on the inlet of the OH-measuring instrument and that corona are easier to generate on lightning rods than on the inlet. In the laboratory, increasing the electric field increased OH, HO 2 , and O 3 , with 14 times more O 3 generated than OH and HO 2 , which were equal. Calculations show that corona on lightning rods can annually generate OH that is 10–100 times ambient amounts within centimeters of the lightning rod and on high-voltage electrical power lines can generate OH that is 500 times ambient a meter away from the corona. Contrary to current thinking, previously unrecognized corona-generated OH, not corona-generated UV radiation, mostly likely initiates premature degradation of high-voltage polymer insulators.