Recently, electrical discharges have been identified as a potentially significant source of the atmosphere's most important oxidant, the hydroxyl radical. Measurements of hydroxyl, the closely related hydroperoxyl radical, and the nitrogen oxides from sparks and subvisible discharges were made in the laboratory under different environmental and electrical conditions representing those found in the troposphere. However, there were still several conditions not yet investigated that could impact hydroxyl and hydroperoxyl production in electrical discharges. In this study, the production of electrically generated hydroxyl and hydroperoxyl (LHOx) and nitrogen oxides (LNOx) was measured under three new conditions not tested previously, including lower pressure, different temperatures, and the presence of cloud droplet‐sized water droplets. In spark discharges, LHOxwas mostly independent of pressure, increased with increasing temperature, and was unaffected by the water droplets. LNOxgeneration was independent of temperature from −10 to 40°C and the presence of water droplets, but increased 1.5‐fold with decreasing pressure. LNOxgeneration was also found to be sensitive to changes in spark intensity and air flow in the laboratory setup. Increasing temperature also made it more likely that a discharge was visible instead of subvisible, but did not impact LHOxproduction in subvisible discharges. Even under these new conditions, the laboratory results agree with results of LHOxfrom a field campaign, demonstrating the relevance of the laboratory experiments to the atmosphere.
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 HOxproduction from lightning has never been quantitatively investigated in the laboratory. In this laboratory study, prodigious amounts of HOxwere 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. HOxand 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 NOxwas approximately independent of both pressure and water vapor over the same ranges. These laboratory measurements of excessive HOxand OH exposure are similar to measurements of electrically generated HOxdiscovered 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 HOxcontribution to atmospheric oxidation.
more » « less- Award ID(s):
- 1834711
- NSF-PAR ID:
- 10448276
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 126
- Issue:
- 9
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
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