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Abstract 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. 

Abstract 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. 

Abstract. The atmosphere's most important oxidizer, the hydroxyl radical (OH), is generated in abundance by lightning, but the contribution of this electrically generated OH (LOH) to global OH oxidation needs to be better quantified. Part of the uncertainty in this contribution is due to the abundant nitric oxide (NO) also generated in lightning, which rapidly removes the LOH before it can oxidize other pollutants in the atmosphere. However, atmospheric observations and a previous laboratory study show extreme LOH coexists with extreme NO. The only way this electrically generated HOx (LHOx) can possibly survive is if LOH production is spatially separated from the NO production in lightning flashes and laboratory sparks. This hypothesis of spatially separate OH and NO production is further tested here in a series of laboratory experiments, where the OH decays were measured from spark discharges in air which had increasing amounts of NO added to it. The LOH decayed faster as more NO was added to the air, indicating that the LOH was reacting with the added NO and not the spark NO. Thus, LOH from lightning flashes is not immediately consumed by the electrically generated NO but is available to oxidize other pollutants in the atmosphere and contribute to global OH oxidation. Subsequent modeling of the laboratory data also supports the spatially separate production of LOH and NO and further suggests that substantial HONO may also be produced by sparks and lightning in the atmosphere. 

The atmosphere’s most important oxidizer, the hydroxyl radical (OH), is generated in abundance by lightning, but the contribution of this electrically generated OH (LOH) to global OH oxidation remains highly uncertain. Part of this uncertainty is due to the abundant nitric oxide (NO) also generated in lightning, which could rapidly remove the LOH before it can oxidize other pollutants in the atmosphere. However, evidence from a previous laboratory study indicated LOH is not immediately consumed by NO, possibly because LOH’s production is spatially separated from the NO production in lightning flashes. This hypothesis of spatially separate OH and NO production is further tested here in a series of laboratory experiments, where the OH decays were measured from spark discharges in air which had increasing amounts of NO added to it. The LOH decayed faster as more NO was added to the air, indicating that the LOH was reacting with the added NO, and not the spark NO. Thus, LOH from lightning flashes is not immediately consumed by the electrically generated NO but is available to oxidize other pollutants in the atmosphere and contribute to global OH oxidation. Subsequent modelling of the laboratory data also supports the spatially separate production of LOH and NO, and further suggests that substantial HONO is also produced by sparks and lightning in the atmosphere.