Removal of Stratospheric O_3 by Radicals: In Situ Measurements of OH, HO_2, NO, NO_2, CIO, AND BrO
Simultaneous in situ measurements of the concentrations of OH, HO_2, ClO, BrO, NO, and NO_2 demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO_2 with ozone, accounted for nearly one-half of the total O_3 removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O_3; reactions involving BrO account for one-half of this loss. Catalytic destruction by NO_2, which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O_3 removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO_2 and ClO are inversely correlated with those of NO and NO_2. The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O_3 removal was inversely correlated with total NO_x, loading.
© 1994 American Association for the Advancement of Science. Received for publication 6 June 1994. Accepted for publication 1 September 1994. We thank the pilots (W. Collette, J. Barrilleaux, D. Krumrey, J. Nystrum, and R. Williams) and the ground crews of the ER-2, without whom this work would not have been possible. ER-2 flight planning by P. A. Newman and co-workers from NASA-Goddard was instrumental to the success of SPADE. The TOMS UV reflectivity is produced by R. D. McPeters and co-workers of the NASA-Goddard ozone processing team; L. Pfister at NASA-Ames was responsible for interpolating this data onto the ER-2 flight track. New instrumentation for OH and HO_2 was developed in part by N. L. Hazen, L. B. Lapson, N. T. Allen, J. F. Oliver, N. W. Lanham, J. N. Demusz, E. E. Thompson, T. L. Martin, E. M. Weinstock, and A. E. Dessler at Harvard University. Interface with the ER-2 was supported by H. Kent, G. Prince, and R. York, at Lockheed; their efforts are gratefully acknowledged. Program support at NASA-Ames by J. C. Arveson, J. L. Barrilleaux, E. Condon, S. Wegner, and S. Hipskind is acknowledged. Finally, this work was supported by the NASA High Speed Research Program, under the direction of H. L. Wesoky, R. S. Stolarski, and M. J. Prather. Additional support for the HO, instrument development came from the NASA Upper Atmosphere Research Program, under the direction of M. J. Kurylo.