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Published August 1982 | Published
Journal Article Open

Radiation and chemistry in the stratosphere: Sensitivity to O_2 absorption cross sections in the Herzberg continuum

Abstract

We propose that a significant overestimate of the molecular oxygen absorption cross sections in the important spectral window from 200-220 nm is in large part responsible for the discrepancy between observed and modeled vertical profiles of some halocarbons (CFCl_3 in particular), as well as for the long-standing problem of simultaneously fitting N_2O, CH_4, CF_2Cl_2 and CFCl_3 profiles with a single eddy diffusion model. Recent measurements of the direct solar flux in the stratosphere by J.R. Herman and co-workers seem to support this idea. Replacing our current O_2 cross sections in the 200-220 nm range by values in better agreement with the results of the above group leads to a reduction in N_2O, CF_2Cl_2 and CFCl_3 concentrations (by factors of 0.70, 0.62 and 0.19, respectively, at 30 km), while CH_4, H_2 and CO profiles are essentially unchanged. Moreover, the predicted concentration of HNO_3 above 30 km is reduced by ∼50%, yielding better agreement with observations. The reduction in O_2 cross sections produces a 10-20% decrease in ozone above about 35 km, but a fairly large increase (∼30%) near the peak around 20-25 km. The changes in other stratospheric species are also briefly discussed.

Additional Information

© 1982 American Geophysical Union. Received April 20, 1982; accepted June 29, 1982. Paper number 2L1124. We thank M. Allen for his assistance in the modeling and discussions concerning the Schumann-Runge bands, and W.B. DeMote for helpful comments. We also thank J.R. Herman, J.E. Frederick and J.E. Mentall for making their work available to us prior to publication and discussing it with us. This research was supported by JPL 49-649-20320-0-3270 to the California Institute of Technology. Contribution number 3776 from the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.

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