Effect of Temperature and Water Droplets on Production of Prodigious Hydrogen Oxides by Electrical Discharges

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 (LHO_x) and nitrogen oxides (LNO_x) 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, LHO_x was mostly independent of pressure, increased with increasing temperature, and was unaffected by the water droplets. LNO_x generation was independent of temperature from −10 to 40°C and the presence of water droplets, but increased 1.5-fold with decreasing pressure. LNO_x generation 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 LHO_x production in subvisible discharges. Even under these new conditions, the laboratory results agree with results of LHO_x from a field campaign, demonstrating the relevance of the laboratory experiments to the atmosphere.