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| Titel |
Production of nitrogen oxides by lightning in a methane-rich early atmosphere |
| VerfasserIn |
Karina Navarro, Rafael Navarro-Gonzalez, Christopher McKay |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077760
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| Zusammenfassung |
| The composition of the early Earth’s atmosphere is not known. Assuming that rapid
weathering of fragments from impacts took placed and efficient sequestration of
carbon occurred in the Earth’s mantle, the early atmosphere would have been mostly
composed of molecular nitrogen with low concentrations of carbon dioxide (less than
percent). In order preserve the existence of oceans, it is required to warm up the
atmosphere almost exclusively with methane [1]. Predicted methane concentrations in the
distant past range from few ppm to several thousand ppm. Photochemical models
predict a production rate of hydrogen cyanide of the order of 6 Tg/yr in a 3 percent
carbon dioxide atmosphere with 1000 ppm of methane [2]. When the atmospheric
levels of carbon dioxide dropped to 0.3 percent but with the methane levels of 1000
ppm, the production rate of hydrogen cyanide increased up to 20 Tg/yr [2]. The
nitrogen fixation rate by lightning in atmospheres dominated bymolecula nitrogen, less
than 10 percent carbon dioxide, and the absence of methane has been reported by
Navarro-Gonzalez et al. [3]. Here we report an experimental study of the effects
of lightning discharges on the nitrogen fixation rate during the evolution of the
Earth’s early atmosphere from 10 to 0.5percent of carbon dioxide with methane
concentrations from 0 to 10,000 ppm in molecular nitrogen. Our results show that the
main nitrogen fixation products by lightning are nitric oxide, nitrous oxide and
methyl nitrite. Preliminary estimates indicate that the production of nitric oxide is not
dependent on the initial concentration of methane and that its production rate decreases
from about 0.02 Tg/yr to about 0.003 Tg/yr in atmospheres ranging from 10 to 0.5
percent of carbon dioxide, respectively. Nitrous oxide is produced by lightning is the
contemporaneous oxygenated Earth’s atmosphere [4], but has not been detected in
nitrogen-carbon dioxide mixtures in the absence of oxygen [5]. This is the first report for the
production of methylnitrate by lightning in the early atmosphere. Further analyses are
underway to accurately determine the production rates of these nitrogen oxides by
lightning, and to understand their role for chemical evolution and early Earth’s
climate.
Zahnle, K. J. Photochemistry of methane and the formation of hydrocyanic acid (HCN) in
the Earths early atmosphere. J. Geophys. Res. 91, 2819-2834 (1986); [2] Tian, F., Kasting,
J.F., and Zahnle, K. Revisiting HCN formation in Earth’s early atmosphere. Earth
Planet. Sci. Lett. 308, 417-423 (2011); [3] Navarro-González, R., McKay, C.P.
and Nna Mvondo, D. A possible nitrogen crisis for archaean life due to reduced
nitrogen fixation by lightning, Nature 412, 61-64 (2001); [4] Levine, J.S., Hughes,
R.E., Chameides, W.L., and Howell, W.E. N20 and CO Production by Electrical
Discharges: Atmospheric Implications, Geophys. Res. Lett.,6, 557-559 (1979);
[5] Nna Mvondo, D. Navarro-González, R, McKay, C.P., Coll, P. and Raulin, F.
Production of nitrogen oxides by lightning and coronae discharges in simulated
early Earth, Venus and Mars environments. Adv Space Res. 27(2), 217-223 (2001). |
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