Estimating the NOx produced by lightning from GOME and NLDN data: a case study in the Gulf of Mexico

[摘要] Nitrogen oxides (NO_xNO+NO₂) play an important role intropospheric chemistry, in particular in catalytic ozone production.Lightning provides a natural source of nitrogen oxides, dominating theproduction in the tropical upper troposphere, with strong impact ontropospheric ozone and the atmosphere's oxidizing capacity. Recent estimatesof lightning produced NO_x (LNO_x) are of the order of 5 Tg [N] peryear with still high uncertainties in the range of one order of magnitude.The Global Ozone Monitoring Experiment (GOME) on board the ESA-satelliteERS-2 allows the retrieval of tropospheric column densities of NO₂ on aglobal scale. Here we present the GOME NO₂ measurement directly over alarge convective system over the Gulf of Mexico. Simultaneously,cloud-to-ground (CG) flashes are counted by the U.S. National LightningDetection Network (NLDN^TM), and extrapolated to includeintra-cloud (IC)+CG flashes based on a climatological IC:CG ratio derivedfrom NASA's space-based lightning sensors. A series of 14 GOME pixels showslargely enhanced column densities over thick and high clouds, coincidingwith strong lightning activity. The enhancements can not be explained bytransport of anthropogenic NO_x and must be due to fresh production of LNO_x. A quantitative analysis, accounting in particular for thevisibility of LNO_x from satellite, yields a LNO_x production of 90(32-240) moles of NO_x, or 1.3 (0.4-3.4) kg [N], per flash. If simplyextrapolated, this corresponds to a global LNO_x production of 1.7(0.6-4.7)Tg [N]/yr.

[学科分类] 大气科学