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Book Chapter

Atmospheric chemistry by large impacts

By
Kevin J. Zahnle
Kevin J. Zahnle
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Published:
January 01, 1990

Impact production of nitric oxide (NO) in the terrestrial atmosphere is calculated over a wide range of impact energies. The model is applied specifically to the Cretaceous/Tertiary impact. Three mechanisms for NO production by impacts are addressed: (1) a primary source caused by the passage of the impactor through the atmosphere; (2) a secondary source caused by the interaction of the atmosphere with the ejecta plume; and (3) a tertiary source caused by widely dispersed ejecta reentering the atmosphere. Thermal radiation from reentering ejecta may also have played a role in setting global fires. The primary source is most important for small impacts; the secondary and tertiary sources dominate for large impacts. Calculated primary and secondary production rates are insensitive to model details; tertiary production is sensitive to the (ill-known) size of the particles that condense directly from the rock vapor plume. Only the tertiary source is global. It can produce globally uniform NO x mixing ratios of order 0.5 percent in the upper stratosphere. The calculated total NO production for a normal impact at 20 km/sec by a 10-km asteroid is ~ × 1014 moles. Larger (or abnormal) impacts can give NO yields of ~1015 ergs. Enormous yields (≥1017 moles) are only achievable in the modern atmosphere by heating most of the atmosphere to at least 1,500°K.

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Contents

GSA Special Papers

Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality

Virgil L. Sharpton
Virgil L. Sharpton
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Peter D. Ward
Peter D. Ward
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Geological Society of America
Volume
247
ISBN print:
9780813722474
Publication date:
January 01, 1990

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