Electrical Discharges Produce Prodigious Amounts of Hydroxyl and Hydroperoxyl Radicals

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 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. HOx and OH exposure were approximately independent of pressure from 360 to 970 hPa and only slightly increased as water vapor increased from 1000 to 8000 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 LHOx contribution to atmospheric oxidation.