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The Global Lightning-Induced Nitrogen Oxides Source

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The Global Lightning-Induced Nitrogen Oxides Source Atmos. Chem. Phys., 7, 3823–3907, 2007 www.atmos-chem-phys.net/7/3823/2007/ Atmospheric © Author(s) 2007. This work is licensed Chemistry under a Creative Commons License. and Physics The global lightning-induced nitrogen oxides source U. Schumann and H. Huntrieser Deutsches Zentrum fur¨ Luft- und Raumfahrt, Institut fur¨ Physik der Atmosphare,¨ Oberpfaffenhofen, 82230 Wessling, Germany Received: 16 January 2007 – Published in Atmos. Chem. Phys. Discuss.: 22 February 2007 Revised: 24 May 2007 – Accepted: 9 July 2007 – Published: 24 July 2007 Abstract. The knowledge of the lightning-induced nitro- about 1 Tg a−1 or 20%, as necessary in particular for under- gen oxides (LNOx) source is important for understanding standing tropical tropospheric chemistry, is still a challeng- and predicting the nitrogen oxides and ozone distributions ing goal. in the troposphere and their trends, the oxidising capacity of the atmosphere, and the lifetime of trace gases destroyed by reactions with OH. This knowledge is further required 1 Introduction for the assessment of other important NOx sources, in par- ticular from aviation emissions, the stratosphere, and from Thunderstorm lightning has been considered a major source surface sources, and for understanding the possible feedback of nitrogen oxides (NOx, i.e. NO (nitric oxide) and NO2 between climate changes and lightning. This paper reviews (nitrogen dioxide)) since von Liebig (1827) proposed it as more than 3 decades of research. The review includes labo- a natural mechanism for the fixation of atmospheric nitro- ratory studies as well as surface, airborne and satellite-based gen (Hutchinson, 1954). Lightning-induced nitrogen oxides observations of lightning and of NOx and related species in (LNOx) have several important implications for atmospheric the atmosphere. Relevant data available from measurements chemistry and climate (WMO, 1999; IPCC, 2001). The in regions with strong LNOx influence are identified, includ- global LNOx source is one of the largest natural sources of ing recent observations at midlatitudes and over tropical con- NOx in the atmosphere (Galloway et al., 2004) and certainly tinents where most lightning occurs. Various methods to the largest source of NOx in the upper troposphere, in partic- model LNOx at cloud scales or globally are described. Previ- ular in the tropics (WMO, 1999). ous estimates are re-evaluated using the global annual mean The LNOx source rate is considered to be the least known ± −1 flash frequency of 44 5 s reported from OTD satellite one within the total atmospheric NOx budget (Lawrence et data. From the review, mainly of airborne measurements near al., 1995; Lee et al., 1997). The global LNOx amount can- thunderstorms and cloud-resolving models, we conclude that not be measured directly, and is difficult to determine. Mod- 25 a “typical” thunderstorm flash produces 15 (2–40)×10 NO elling of the horizontal and vertical distribution of lightning molecules per flash, equivalent to 250 mol NOx or 3.5 kg of and the LNOx source is highly uncertain (Price and Rind, N mass per flash with uncertainty factor from 0.13 to 2.7. 1992; Pickering et al., 1998). Previous reviews of LNOx dis- Mainly as a result of global model studies for various LNOx cuss theoretical, laboratory, and field studies to determine the parameterisations tested with related observations, the best amount of LNOx (Tuck, 1976; Drapcho et al., 1983; Borucki estimate of the annual global LNOx nitrogen mass source and Chameides, 1984; Biazar and McNider, 1995; Lawrence −1 and its uncertainty range is (5±3) Tg a in this study. In et al., 1995; Levy II et al., 1996; Lee et al., 1997; Price et spite of a smaller global flash rate, the best estimate is es- al., 1997b; Huntrieser et al., 1998; Bradshaw et al., 2000; Ri- sentially the same as in some earlier reviews, implying larger dley et al., 2005), mainly by extrapolating measurements of flash-specific NOx emissions. The paper estimates the LNOx emissions from individual lightning or thunderstorm events accuracy required for various applications and lays out strate- to the global scale (Chameides et al., 1977, 1987). Only gies for improving estimates in the future. An accuracy of a few papers review the determination of the global LNOx source by fitting models to observations (Levy II et al., 1996; Correspondence to: U. Schumann Zhang et al., 2003b). The majority of studies since the mid- ([email protected]) 1990s, as reviewed in this paper, assumed a best-estimate Published by Copernicus Publications on behalf of the European Geosciences Union. 1 Figures 2 3 3824 U. Schumann and H. Huntrieser: The global lightning-induced nitrogen oxides source relative importance of aviation NOx for uncertain LNOx con- -3 4 8 tributions (Sect. 2.9), and derives requirements on LNOx ac- cm 5 curacy (Sect. 2.10). Thereafter, the paper reviews the various 3 6 -1 methods to constrain the LNOx source values (Sect. 3). It re- s -3 evaluates results from flash (Sect. 3.1) and storm (Sect. 3.2) extrapolations using the most recent satellite observations of 2 4 cm 4 OH production rate, the global lightning frequency. In addition, the paper reviews 10 3 P(O3) for the first time the results of a large number of global model 1 2 studies discussing LNO impact on tropospheric chemistry Net O Net x OH concentration, 10 (Sect. 3.3). Section 3.3 also elaborates on the potential of 0 0 better constraining the LNOx source estimate using global 0.001 0.01 0.1 1 10 model fits to observations of concentrations and deposition -1 4 NOx mixing ratio, nmol mol fluxes of nitrogen compounds and other species. Finally, Sect. 4 presents the conclusions. 5 Figure 1. Dependence of the OH concentration and the net O3 production rate on the NOx 6 Fig.mixing 1. ratioDependence calculated with ofa steady the OHstate box concentration model for diurna andl average the in net June O at3 10pro- km duction rate on the NOx mixing ratio calculated with-1 a steady state- 7 altitude and 45° latitude; background mixing ratios of O3: 100 nmol mol ; H2O: 47 μmol mol◦ 8 box1; CO: model 120 nmol for mol diurnal-1; CH : 1660 average nmol mol in-1; replotted Juneat from 10 Ehhalt km and altitude Rohrer (1994) and 45with 4 −1 2 Review of LNOx contributions and their importance 9 latitude;kind permission background of Woodhead mixing Publishing ratios Limited. of O3: 100 nmol mol ;H2O: 47 µmol mol−1; CO: 120 nmol mol−1; CH : 1660 nmol mol−1; re- 4 2.1 Importance of NO for atmospheric chemistry plotted from Ehhalt and Rohrer (1994) with kind permission of x Woodhead Publishing Limited. Nitrogen oxides are critical components of the troposphere which directly affect the abundance of ozone (O3) (Crutzen, −1 1974) and the hydroxyl radical (OH) (Levy II, 1971; Rohrer value of about 5 Tg a (NOx source values are given in ni- and Berresheim, 2006). Ozone is known as a strong oxidant, trogen mass units per year in this paper), with an uncertainty −1 a strong absorber of ultraviolet radiation, and a greenhouse range 1–20 Tg a . Extreme estimates of the LNOx source −1 −1 gas (WMO, 1999). Ozone is formed and destroyed by pho- rate such as 0.2 Tg a (Cook et al., 2000) and 220 Tg a tochemistry and the net production rate depends nonlinearly (Franzblau and Popp, 1989; Liaw et al., 1990), implying 163 on the abundance of NOx present (Liu, 1977), see Fig. 1. the global LNOx contribution from minor to overwhelming, In regions with low NOx level (e.g. in the tropical marine are now considered inconsistent with measured atmospheric boundary layer), the net effect is an O3 destruction. In re- NOx concentrations and nitrate deposition values (Gallardo gions with NOx concentrations above a critical level (but not and Rodhe, 1997). very high), e.g. in the upper troposphere, O3 production dom- Considerable progress has been made recently which al- inates. The critical NOx level depends on the O3 mixing ratio − lows reducing the uncertainty of the global LNOx value. This and may be as low as 5 pmol mol 1 in the oceanic boundary includes satellite observations of global lightning (Christian layer with typically low ozone values (Crutzen, 1979), 10– − et al., 2003), satellite observations of NO2 column distribu- 50 pmol mol 1 in the free troposphere (Fishman et al., 1979; tions (Burrows et al., 1999), airborne in-situ measurements Ehhalt and Rohrer, 1994; Brasseur et al., 1996; Davis et al., of NOx abundance near thunderstorms at midlatitudes (Dye 1996; Kondo et al., 2003b), and increases with the ambient et al., 2000; Huntrieser et al., 2002; Ridley et al., 2004) and O3 concentration (Grooß et al., 1998). Hence, in regions re- over tropical continents, where most lightning occurs (see mote from strong local pollution, O3 production increases Sect. 2.4), detailed cloud-resolving model studies (DeCaria with NOx concentration (is “NOx limited”). The relative in- et al., 2000; Fehr et al., 2004), and improved global models crease of O3 production is largest for low NOx concentra- (Dentener et al., 2006; van Noije et al., 2006). tions. This paper reviews the present knowledge on the global The concentrations of HOx including OH, the hydroper- LNOx source rate. It describes the importance of NOx for oxyl radical HO2 and other peroxy radicals, depend also non- tropospheric chemistry (Sect. 2.1). It reviews knowledge linearly on the NOx abundance (Logan et al., 1981; Ehhalt on the NOx concentrations, sources and sinks (Sect. 2.2), and Rohrer, 1994; Jaegle´ et al., 1999; Olson et al., 2006), the essential lightning properties (Sect. 2.3), and the forma- see again Fig.
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