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El Chichon Volcanic Aerosols: Impact of Radiative, Thermal, and Chemical Perturbations

Michelangeli, Diane V. and Allen, Mark and Yung, Yuk L. (1989) El Chichon Volcanic Aerosols: Impact of Radiative, Thermal, and Chemical Perturbations. Journal of Geophysical Research D, 94 (D15). pp. 18429-18443. ISSN 0148-0227. doi:10.1029/JD094iD15p18429.

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We examine the consequences of the eruption of the El Chichon volcano on the Earth's stratospheric chemistry. Formed after the eruption, the volcanic aerosol cloud, with a peak particle density at 27 km, was very efficient at altering the radiation field. The results of a one-dimensional radiative transfer model show that the total radiation increased by 8% within the aerosol layer longward of 3000 Å. At certain altitudes and wavelengths below 3000 Å, the total radiation decreased by 15%. Consequently, there are changes in the photolysis rates obtained with a one-dimensional photochemical model: for example, O_2 photodissociation rate constants decrease by 10%, while O_3 photodissociation rate constants increase by a comparable amount. A combination of this radiation change and the effect of a temperature variation of a few degrees causes the abundance of O_3 to decrease by 7% at 24 km, in good agreement with the Solar Backscattered Ultraviolet experiment (SBUV) measurements of a 5–10% decrease. The combined radiative and thermal perturbations on the concentrations of O, O(1D), OH, HO_2, H_2O_2, NO, NO_2, NO_3, N_2O_5, HNO_3, HO_2NO_2, Cl, ClO, ClO_2, HOCl, ClNO_3, and HCl are computed and presented in detail. However, these changes as calculated are insufficient to explain the observations of significant decreases in NO and NO_2 and increases in HCl. A heterogeneous reaction catalyzed by aerosol surfaces which transforms ClNO_3 into HCl provides a pathway for sequestering NO_x, and at the same time reduces ClNO_3 in favor of HCl. The inclusion of this reaction in the model leads to a satisfactory single-step explanation of the otherwise puzzling observations of NO, NO_2, and HCl. The observed lack of change in HNO_3 cannot be explained by this hypothesis. The effects of a number of heterogenous reactions, some believed to be important for the Antarctic stratosphere, have been assessed with our model. We also examine the hypothesis of direct injection of gases from the volcano into the stratosphere. Only an unrealistically large injection (60% column increase above 12 km) results in an HCl increase in agreement with observations. An equally large water injection decreases HCl, and decreases the NO and NO_2 by as much as 20%, but still does not simulate the observed NO_x decrease.

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Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 1989 by the American Geophysical Union. Received September 30, 1988; revised May 30, 1989; accepted May 30, 1989. Paper number 89JD01149. The authors wish to thank T. P. Ackerman and J. B. Pollack for providing the results of their optical calculations. Communications, prior to publication, from W. G. Mankin, B. A. Ridley, M. McFarland, S. Chandra, and T. Clancy are greatly appreciated. This work has also benefited from numerous discussions with M. J. Molina, M. T. Leu, R. R. Friedl, S. P. Sander, and W. B. DeMore. The comments of S. Solomon and anonymous reviewers have helped us improve the manuscript. This research was supported by NASA grant NAGW-413. Division of Geological and Planetary Sciences, California Institute of Technology, contribution 4197.
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Caltech Division of Geological and Planetary Sciences4197
Issue or Number:D15
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Official Citation:Michelangeli, D. V., M. Allen, and Y. L. Yung (1989), El Chichon volcanic aerosols: Impact of radiative, thermal, and chemical perturbations, J. Geophys. Res., 94(D15), 18429–18443, doi:10.1029/JD094iD15p18429.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49945
Deposited By: Ruth Sustaita
Deposited On:23 Sep 2014 20:19
Last Modified:10 Nov 2021 18:49

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