Electrical Discharges Produce Prodigious Amounts of Hydroxyl and Hydroperoxyl Radicals. Issue 9 (5th May 2021)

• Record Type: Journal Article
• Authors: Jenkins, Jena M.; Brune, William H.; Miller, David O.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-05
• Subjects: electrical discharges -- hydroperoxyl radical -- hydroxyl radical -- lightning -- nitrogen oxides -- ozone; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD034557
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: 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. Plain Language Summary: Lightning is known to generate nitrogen oxides and ozone, which indirectly create the hydroxyl radical (OH), the atmosphere's primary oxidant. This laboratory study proves that the weak visible electrical discharges associated with lightning flashes generate extreme amounts of OH and the hydroperoxyl radical (HO2 ) directly, and, surprisingly, so do weak electrical subvisible discharges. Further, the abundant OH generated is in similar amounts for all tropospheric pressures, varies little over a wide range of water vapor, exists much longer than expected, and is comparable to amounts seen in electrified thunderstorms during a 2012 airborne study. Thus, atmospheric electrical discharges are likely an important source of oxidation throughout the lower atmosphere. Key Points: Abundant hydroxyl and hydroperoxyl radicals generated by electric discharges were measured in the laboratory for the first time Measured hydroxyl and hydroperoxyl radical mixing ratios showed small to no dependence on pressure and water vapor mixing ratio The laboratory results are consistent with the extreme amounts of hydroxyl and hydroperoxyl radicals observed in thunderstorm anvils