NOx production by lightning over the continental United States

The production of NOx by lightning over the contiguous United States has been evaluated by using combined ground-based and satellite lightning measurements. The lightning data from the National Lightning Detection Network (NLDN) over the period of 1995-1999, along with a ratio of intracloud (IC) to cloud-to-ground (CG) flashes derived in conjunction with satellite lightning measurements from the Optical Transient Detector (OTD), are analyzed to obtain the number of CG and IC flashes. The average annual lightning counts over the 5-year period are about 23 million for CG flashes and 55 million for IC flashes. The resulting lightning distributions are employed to calculate the production of NOx assuming a NO production rate of 6.7 x 10(26) molecules for each CG flash and 6.7 x 10(21) molecules for each IC flash. NOx production by lightning varies seasonally in accordance with the lightning distribution, with the maximum production occurring in the summer (June, July, and August) and in the Southeast. CG flashes produce more NOx than IC flashes despite fewer CG flashes by a factor of 2 or more. The geographical and seasonal production of NOx by lightning is compared to NOx emissions from other sources (i.e., from anthropogenic, soil, and biomass-burning emissions). The results indicate that regional emissions of NOx by lightning can be significant in the summertime and may play a critical role in ozone formation in the free troposphere. Our estimate of NOx emission by lightning over the United States would decrease by an order of magnitude if we use the production rates from a recent laboratory study [Wang et al., 1998] that are significantly lower than previous estimates

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

Nitrogen oxides (NO_xNO+NO₂) play an important role in tropospheric chemistry, in particular in catalytic ozone production. Lightning provides a natural source of nitrogen oxides, dominating the production in the tropical upper troposphere, with strong impact on tropospheric ozone and the atmosphere's oxidizing capacity. Recent estimates of lightning produced NO_x (LNO_x) are of the order of 5 Tg [N] per year with still high uncertainties in the range of one order of magnitude. <P style='line-height: 20px;'> The Global Ozone Monitoring Experiment (GOME) on board the ESA-satellite ERS-2 allows the retrieval of tropospheric column densities of NO₂ on a global scale. Here we present the GOME NO₂ measurement directly over a large convective system over the Gulf of Mexico. Simultaneously, cloud-to-ground (CG) flashes are counted by the U.S.&nbsp;National Lightning Detection Network (NLDN<SUP><SMALL>TM</SMALL></SUP>), and extrapolated to include intra-cloud (IC)+CG flashes based on a climatological IC:CG ratio derived from NASA's space-based lightning sensors. A series of 14&nbsp;GOME pixels shows largely enhanced column densities over thick and high clouds, coinciding with strong lightning activity. The enhancements can not be explained by transport of anthropogenic NO_x and must be due to fresh production of LNO_x. A quantitative analysis, accounting in particular for the visibility 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 simply extrapolated, this corresponds to a global LNO_x production of 1.7 (0.6-4.7)Tg [N]/yr

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

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