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Accurate measurements of global lightning are essential for understanding present and future atmospheric electricity, composition, and climate. The latest space‐based lightning detector, the Geostationary Lightning Mapper (GLM), was the first to be placed in geostationary orbit, with a continuous view of most of the American continents. Prior to the GLM, the Lightning Imaging Sensor (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite collected lightning measurements from which numerous lightning climatologies have been developed, including those used in global models. However, this study finds that both the GLM and a second, similar LIS placed on the International Space Station (ISS) in 2017 detect lightning at similar rates and are undercounting lightning compared to ground‐based Lightning Mapping Arrays (LMAs). The GLM undercounts lightning by an average factor of 7.0, reaching a maximum over 120 as a function of satellite zenith angle, radar reflectivity at a height where the temperature is −10°C, flash height, and thunderstorm polarity. The LIS is estimated to undercount lightning by an average factor of 5.6, reaching a maximum of 75.0 as a function of radar reflectivity at the −10°C level, flash height, and thunderstorm polarity. Preliminary predictive equations for the GLM and LIS lightning undercount factor, or scaling factor (SF), use ice‐water content, equilibrium level, flash height, and satellite zenith angle, all of which can be derived in models. These equations are developed to encourage updating lightning parameterizations within global models and will likely increase modeled lightning's effects on atmospheric electrical circuits, composition, chemistry, and climate change.

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_xwas mostly independent of pressure, increased with increasing temperature, and was unaffected by the water droplets. LNO_xgeneration was independent of temperature from −10 to 40°C and the presence of water droplets, but increased 1.5‐fold with decreasing pressure. LNO_xgeneration 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_xproduction in subvisible discharges. Even under these new conditions, the laboratory results agree with results of LHO_xfrom a field campaign, demonstrating the relevance of the laboratory experiments to the atmosphere.

Prodigious amounts of the hydroxyl radical (OH) are generated in the laboratory on tree leaves by corona discharges, which also occur on trees during thunderstorms. Production rates of OH and HO₂depend on the applied electric field generating the corona discharge, leaf dryness, and the presence of liquid water on the leaf. However, they are independent of leaf type and corona discharge polarity for a given corona ultraviolet (UV) flux. Production rates of OH, HO₂, and O₃strongly correlate with corona UV flux. Although the contribution of corona‐produced OH to total global OH production is unlikely to be important, corona‐generated OH is likely a few orders of magnitude greater than oxidation by known processes in the vicinity of the affected leaves, potentially influencing atmospheric oxidation and tree and forest ecology.

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 HO₂were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO₂is orders of magnitude greater 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 to 16% of global atmospheric OH oxidation.

The Focused Isoprene eXperiment at the California Institute of Technology (FIXCIT) was a collaborative atmospheric chamber campaign that occurred during January 2014. FIXCIT is the laboratory component of a synergistic field and laboratory effort aimed toward (1) better understanding the chemical details behind ambient observations relevant to the southeastern United States, (2) advancing the knowledge of atmospheric oxidation mechanisms of important biogenic hydrocarbons, and (3) characterizing the behavior of field instrumentation using authentic standards. Approximately 20 principal scientists from 14 academic and government institutions performed parallel measurements at a forested site in Alabama and at the atmospheric chambers at Caltech. During the 4 week campaign period, a series of chamber experiments was conducted to investigate the dark- and photo-induced oxidation of isoprene, α-pinene, methacrolein, pinonaldehyde, acylperoxy nitrates, isoprene hydroxy nitrates (ISOPN), isoprene hydroxy hydroperoxides (ISOPOOH), and isoprene epoxydiols (IEPOX) in a highly controlled and atmospherically relevant manner. Pinonaldehyde and isomer-specific standards of ISOPN, ISOPOOH, and IEPOX were synthesized and contributed by campaign participants, which enabled explicit exploration into the oxidation mechanisms and instrument responses for these important atmospheric compounds. The present overview describes the goals, experimental design, instrumental techniques, and preliminary observations from the campaign. This work provides context for forthcoming publications affiliated with the FIXCIT campaign. Insights from FIXCIT are anticipated to aid significantly in interpretation of field data and the revision of mechanisms currently implemented in regional and global atmospheric models.